substituent effects on the electronic properties of complexes with dipyridophenazine and triazole...

Accepted Manuscript

Title: Substituent effects on the electronic properties ofcomplexes with dipyridophenazine and triazole ligands:electronically connected and disconnected ligands

Author: Holly van der Salm Anastasia B.S. Elliott Keith C.Gordon

PII: S0010-8545(14)00141-6DOI: http://dx.doi.org/doi:10.1016/j.ccr.2014.05.003Reference: CCR 111870

To appear in: Coordination Chemistry Reviews

Received date: 11-12-2013Revised date: 14-4-2014Accepted date: 2-5-2014

Please cite this article as: Holly van der Salm, Anastasia B.S. Elliott, Keith C. Gordon,Substituent effects on the electronic properties of complexes with dipyridophenazineand triazole ligands: electronically connected and disconnected ligands, CoordinationChemistry Reviews (2014), http://dx.doi.org/10.1016/j.ccr.2014.05.003

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http://dx.doi.org/doi:10.1016/j.ccr.2014.05.003

http://dx.doi.org/10.1016/j.ccr.2014.05.003

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Substituent effects on the electronic properties of

complexes with dipyridophenazine and triazole ligands:

electronically connected and disconnected ligands

Holly van der Salma, Anastasia B. S. Elliotta, Keith C. Gordona,∗

aDepartment of Chemistry and MacDiarmid Institute for Advanced Materials andNanotechnology, University of Otago, PO box 56, Dunedin 9054, New Zealand.

Abstract

Substituent effects may tune and alter the optical and electronic properties

of ligands and the complexes which they comprise. We review the effect of

electron-withdrawing and -donating groups on the dipyridophenazine (dppz)

framework. The observation of selected modulation of the properties asso-

ciated with the phenazine or phenanthroline MOs is observed and reflected

in the electrochemical and optical properties. The effect of donor groups

that can give rise to ligand-centered charge-transfer optical transitions is

also discussed. The effect of substituents on complexes with triazole ligands

is examined; in stark contrast to the findings for dppz systems, and virtually

regardless of the type of triazole ligand, substituents have only a muted effect

on optical and electrochemical properties.

Keywords:

dipyridophenazine, triazole, spectroscopy, photophysics, electrochemistry,

∗Corresponding authorEmail address: [email protected] (Keith C. Gordon)

Preprint submitted to Coordination Chemistry Reviews April 14, 2014

Manuscript

http://ees.elsevier.com/ccr/viewRCResults.aspx?pdf=1&docID=1792&rev=2&fileID=81943&msid=6C52B148-5476-4E7B-8AFE-AC87B8B54198

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Contents1

1 Introduction 32

2 Substituents on dppz ligands 43

2.1 Electron-withdrawing substituents . . . . . . . . . . . . . . . . 64

2.2 Electron-donating substituents . . . . . . . . . . . . . . . . . . 175

2.3 Intra-ligand charge-transfer systems . . . . . . . . . . . . . . . 256

3 Triazole Ligands 277

3.1 Pyridyl Triazoles . . . . . . . . . . . . . . . . . . . . . . . . . 308

3.1.1 Substitution on the Triazole . . . . . . . . . . . . . . . 309

3.1.2 Substitution on the Pyridine . . . . . . . . . . . . . . . 3710

3.1.3 Different Triazole Configurations . . . . . . . . . . . . 3911

3.2 Other Triazole Heterocycles . . . . . . . . . . . . . . . . . . . 4412

3.3 Bridging triazole ligands . . . . . . . . . . . . . . . . . . . . . 4913

4 Conclusions 5114

5 Acknowledgements 5115

6 References 5216

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1. Introduction17

The use of substituents on ligands to imbue changes in electronic or18

steric properties has been used advantageously for decades. An example of19

this is the use of phenyl groups at the 4,7 positions of 1,10-phenanthroline20

(bathophenanthroline) to redshift the metal-to-ligand charge transfer21

(MLCT) transition of iron(II) complexes from 510 nm for [Fe(phen)3]2+ to22

533 nm for [Fe(4,7-Ph2phen)3]2+ [1]. Using appropriate substituents it is23

possible to reprogram the 1,10-phenanthroline ligand to bind copper(I) in24

preference to iron(II). Substitution at the 2,9 positions inhibits octahedral25

coordination and favors a tetrahedral geometry. Using phenyl groups it26

is possible to alter the intensity of the MLCT transitions associated with27

the [Cu(L)2]+ by extending or diminishing the charge-transfer length [2].28

All of these effects are predicated upon the electronic connectivity of the29

parent ligand framework. A number of physical properties can inform on30

substituent effects. The lowest energy absorption gives a convenient method31

of observing substituent effects by modulation of the HOMO and LUMO32

energies [3]. These may also be probed using electrochemistry [4]. The33

alteration of MO energies can result in distinct changes to excited state34

properties; notably quantum yields and excited state lifetimes [5]. These35

methods allow for analysis of the effect of substituent groups. In this review36

we discuss the effect of electron donor and acceptor moieties on the electronic37

properties for two classes of ligand. The first of these is dipyrido[3,2-a:2’,3’-38

c]phenazine (dppz) which has a level of electronic connectivity imbued by39

its distinct electronic structure in which the unoccupied molecular orbitals40

are partitioned over different sections of the ligand. In the second section41

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we review triazole–based ligands in which electronic connectivity is rather42

poor and thus substituent effects can be subtle.43

2. Substituents on dppz ligands44

The effect of substituents on the optical properties of both a ligand and45

various metal complexes can be exemplified in dppz. The nature of the molec-46

ular orbitals in this ligand means the position of substituents can lead to quite47

different effects. There are a number of positions in which the dppz ligand can48

be substituted, see Figure 1, and substituents can be broadly separated into49

electron-withdrawing and electron-donating groups. The nature and position50

of substituents have been shown to affect the optical and electronic properties51

of dppz ligands, as well as metal complexes which contain them, and this has52

been investigated in a number of contexts [6]. Ru complexes of dppz are well53

known for switchable emission behaviour, in that strong emission is observed54

in aprotic solvents, but this is quenched in the presence of protic solvents or55

DNA. The origin of this ‘light-switch’ effect, which is caused by an interplay56

between emissive MLCT(phen) and dark MLCT(phz) states was originally57

thought to be due to a change in energy of the MLCT(phz), stabilised by58

coordination of protic solvents to the phenazine nitrogens [7]. However, vari-59

able temperature emission spectroscopy revealed that [Ru(bpy)2(dppz)]2+ in60

nitrile solvents and alcohols exhibits a ‘roll-over’ effect, in which increasing61

the temperature increased the emissive lifetime up to a certain temperature,62

and then decreased it again (see Figure 2) [8]. This behaviour differs signif-63

icantly from that of [Ru(bpy)3]2+. The explanation for ‘roll-over’ behaviour64

was that there is an equilibrium between the lower energy MLCT(phz) state65

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N N

N

1

2

3

4

5

6

7

89 10

11

12

1314

A

B

C

D E

Figure 1: Numbering scheme and ring labelling for dppz.

and the higher energy MLCT(phen) state, in which the dark state is en-66

thalpically favoured, and the bright state entropically favoured. Thus at67

low temperatures the MLCT(phz) state is populated and no emission is ob-68

served; with increasing temperature the bright MLCT(phen) state begins to69

be populated, and the ‘roll-over’ effect occurs because at sufficiently high70

temperatures the MLCT(phen) state is depopulated via thermal population71

of metal-based d-d states, well-known in Ru compounds [8].72

Substituent effects are also very interesting because they can alter73

relative MO energies and hence the equilibrium between excited states.74

[Ru(bpy)2(dppzMe)]2+ showed similar behaviour to the unsubstituted75

compound in alcohol solvents, but in nitrile solvents the bright state was76

populated at all temperatures, attributed to either a sufficiently small energy77

gap between the two states that thermal population is always possible, or78

a reverse in the state order causing MLCT(phen) to be entropically and79

enthalpically favoured [8]. This study exemplifies the effect substituents80

can have on the electronic structure of dppz, and also the environmental81

sensitivity of dppz compounds.82

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MLCT(phz)

MLCT(phen)

Figure 2: Energy level diagram depicting excited states of [Ru(bpy)2(dppz)]2+, where CN

and OH refer to nitrile and alcohol solvents respectively. Figure modified from Brennaman

et al [8].

2.1. Electron-withdrawing substituents83

Electron withdrawing substituents on the phenazine section (on the E-84

ring at 11 and/or 12 positions, see Figure 1) have been widely utilised,85

and these include symmetrical and unsymmetrical substitution patterns with86

groups such as Cl, CN, NO2, COOH/COOR, CF3, F and Br. The dppz lig-87

and shows electronic absorption bands in the UV region, with lowest energy88

bands (340-380 nm, ε ∼1×104 M−1 cm−1) n,π* in nature and higher energy89

bands (270-290 nm, ε ∼2.5×104 M−1 cm−1) π, π* in nature [9, 10, 11]. Metal90

complexation causes a red-shift in absorption bands and in most cases the91

lowest energy absorption then becomes MLCT in nature; this may be a tail92

or a distinct band depending on the metal, but tends to have lower oscillator93

strength than ligand-centered transitions.94

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Table 1: Electrochemical data for dppz with electron withdrawing substituents at 11

and/or 12 positions (1). Compounds discussed in some detail in the text are shown in

bold.

Ligand Eox Ered Solvent Standard electrode Reference

dppz -1.34 DCM Fc/Fc+ [12]

-1.64, -2.26 DMF Fc/Fc+ [13]

-1.28 DCM SCE [14]

dppzCl2 -0.83 DMF Ag/AgCl [15]

-1.42, -2.14 DMF Fc/Fc+ [13]

-0.93 DCM SCE [9]

dppzCl -1.53, -2.31 DMF Fc/Fc+ [13]

dppzBr -1.11 DCM DMFc/DMFc+ [16]

[Re(CO)3Cl(dppzF2)] -1.32, -1.68 DCM Fc/Fc+ [17]

dppz(NO2)2 -0.27 DMF Ag/AgCl [15]

-1.35, -1.83 DCM Fc/Fc+ [18]

dppz(NO2) -0.655, -1.178 DMF SCE [10]

-1.19, -1.74 DMF Fc/Fc+ [13]

-1.50, -1.95 DCM Fc/Fc+ [18]

-1.08, -1.56 MeCN Ag/AgCl [19]

-1.05 DCM SCE [9]

[Re(CO)3Cl(dppz(CF3)2)] -1.05, -1.77 DCM Fc/Fc+ [17]

dppz(CF3) -1.38, -2.14 DMF Fc/Fc+ [13]

[Ru(bpy)2(dppz(CN)2)]2+ -0.54, -1.12 MeCN Ag/AgCl [20]

dppzCN -0.91 DCM or MeCN SCE [21]

-0.74, -1.50 DMF Ag/AgCl [15]

dppz(COOH) -0.7, -1.18 DMF SCE [10]

dppz(COOEt) -1.07 DCM DMFc/DMFc+ [16]

dppz(oxa) 1.69 -0.85 DCM or MeCN SCE [21]

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N N

N X

Y

X=Y=H X=Y=Cl X=Y=Br X=Y=F X=Cl, Y= H X=Br, Y=H X=Y=NO2

X=NO2, Y=H X=Y=CF3

X=CF3, Y=H X=Y=CN X=CN, Y=H X=COOH, Y=H X=COOPh, Y=H X=COOEt, Y=H X=oxadiazole, Y=H

X=Y=CH3

X=Y=OCH3

X=CH3, Y=HX=OCH3, Y=HX=Y=NH2

X=NH2, Y=HX=Y=CH2BrX=Y=PhX=Y=Ph-PhX=Y=Ph-(C(CH3)3)X=Y=PhacX=Y=SCNX, Y = S2CSX=Y=SC10H23

X=Ph(NH2)2, Y=H

S

S

S

= Phac

=S2CS

N N

O

=oxadiazole

dppzdppzCl2dppzBr2dppzF2dppzCldppzBrdppz(NO2)2dppz(NO2)dppz(CF3)2dppz(CF3)dppz(CN)2dppz(CN)dppz(COOH)dppz(COOPh)dppz(COOEt)dppz(oxa)

dppzMe2dppz(OMe)2

dppzMedppz(OMe)dppz(NH2)2dppz(NH2)dppz(CH2Br)2

dppz(Ph)2

dppz(Ph-Ph)2

dppz(Ph-tBu)2

dppz(Phac)2

dppz(SCN)2dppz(S2CS)dppz(Sdec)2dppz(Ph(NH2)2)

Figure 3: 11,12-substituents. Compounds discussed in some detail in the text are shown

in bold.

Table 2: Electronic absorption and emission data for electron withdrawing substituents.

Compounds discussed in some detail in the text are shown in bold.

Ligand λabs (ε×104 M−1

cm−1)

λem (Φ) Solvent Reference

dppz 290 (2.5), 340 (0.9),

350 (1.0), 359 (1.3),

367 (1.2), 379 (1.4)

DMF [11]

270 (4.37), 367

(1.13), 379 (1.29)

DCM [9]

dppzCl2 272 (5.39), 370

(1.54), 391 (2.13)

DCM [15]

295 (2.4), 371 (1.8),

392 (2.6)

543 (1.63×10-3) DMF [13]

391 (2.14) 415 (0.008) DCM [22]

272 (5.39), 370

(1.54), 391 (2.13)

DCM [9]

dppzCl 292 (2.1), 366 (1.4),

386 (1.7)

515 (6.60×10-4) DMF [13]

dppzBr2 237, 297, 373, 392 420 DCM [23]

Continued on next page

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Ligand λabs λem (Φ) Solvent Reference

dppzBr 279 (2.83), 329

(0.70), 366 (0.61),

385 (0.68)

420 [16, 24]

[Re(CO)3Cl

(dppzF2)]

262 (sh), 276 (5.4),

319 (1.4), 360 (1.1),

380 (0.9), 400 (sh)

[17]

dppz(NO2)2 228 (5.45), 233

(5.25), 249 (4.40),

293 (2.01), 304

(1.67), 389 (0.61)

DCM [15]

dppz(NO2) 298, 307, 372, 389 DMF [10]

298 (4.2), 373 (1.6),

391 (1.1)

513 (4.67×10-2) DMF [13]

390 (4.21), 500

(2.80)

[25]

246 (4.64), 254

(4.23), 287 (4.54),

295 (4.76), 303

(4.05), 368 (1.79),

386 (1.49)

DCM [18]

297 (4.31), 306

(3.84), 371 (1.61),

389 (1.31)

DCM [9]

[Re(CO)3Cl

(dppz(CF3)2)]

265 (6.5), 273 (7.7),

297 (2.7), 315 (1.8),

343 (1.2), 357 (1.3),

400 (sh)

[17]

dppz(CF3) 293 (2.7), 360 (1.4),

379 (1.4)

521 (4.99×10-3) DMF [13]

[Ru(bpy)2

(dppz(CN)2)]2+

440 (1.64) 617 (0.005) [20]

dppzCN 271 (2.28), 351

(sh), 357 (sh), 367

(0.63), 376 (sh),

388 (0.67)

438 [21, 24]


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271 (5.86), 295

(3.79), 305 (2.7),

367 (1.7), 387 (1.8)

DMF [15]

dppz(COOH) 276, 366, 386 DMF [10]

dppz(COOEt) 276 (3.02), 348

(0.53), 356 (0.60),

366 (0.82), 374

(0.67), 386 (0.81)

424 DCM [16]

[Ru(phen)2

(dppz(COOPh))]2+

379, 439 612 (0.01) H2O [26]

660 (0.034) MeCN [26]

dppz(oxa) 276 (4.07), 349

(0.72), 367 (0.95),

376 (sh), 385

(1.10), 400 (0.88)

427 (0.04) [21]

Studies have shown the first reduction (Ered) of dppz to be phenazine-95

based [11, 27], and hence this value is significant in order to assess how the96

phenazine orbital is altered by substitution. The Ered for unsubstituted dppz97

and its Cu and Re complexes in DCM ahve values of -1.28, -1.25 and -1.0198

V vs SCE respectively. This suggests that Re affects the phz MO energy but99

Cu does not [12]. In DMF, dppz emits at 535 nm (400 nm excitation) with a100

quantum yield of 12.3×10-3 [13], in DCM emission is observed at 502 nm[28].101

Electron-withdrawing substituents at the phz MO (see Figure 1, posi-102

tions 10→13) lower the LUMO energy which is manifested as a red-shift in103

absorption spectra. The LUMO is predominantly phz-based, although it can104

delocalise across the substituent [15]. Using DFT calculations for dirhodium105

complexes it was found that the LUMO had a higher % phz contribution106

the more electron-withdrawing the substituents, which also corresponded to107

a more positive Ered value [15]. The ligands dppzCl2, dppzBr2 and dppzF2108

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all show Ered more positive than dppz and a red-shift in absorption bands109

(Tables 1 and 2) [9, 15]. The ligand dppzBr2 shows emission red-shifted rel-110

ative to dppzCl2 in DCM (420 nm [23] and 415 nm [22] respectively). Re111

and Cu complexes of dppzCl2 show lower energy MLCT transitions than the112

equivalent dppz complexes, and also an MLCT THEXI state rather than113

the more commonly observed ligand-centered state [9]. Resonance Raman114

spectroscopy has been used to show that [Ru(tbbpy)2(dppzBr2)]2+ (where115

tbbpy = 4,4’-di-tertbutyl-2,2’-bipyridine) most likely has MLCT(dppzBr2)116

as the lowest energy transition, rather than MLCT(bpy) which is observed117

for [Ru(bpy)2(dppz)]2+. The compound was probed across the lowest energy118

transition, see Figure 4, and by comparison to the Raman spectra of the119

ligand dppzBr2 and the related complex [Ru(tbbpy)3]2+, the enhanced vibra-120

tional modes were assigned to dppzBr2, with possible small enhancement of121

tbbpy bands suggesting there may be a small contribution of MLCT(tbbpy)122

to the main MLCT(dppz) absorption manifold [23].123

The ligand dppzF2 has been reported as the [Re(CO)3Cl] complex which124

shows consistent electron-withdrawing group behaviour [17], while transient125

resonance Raman spectra show only a singlet π, π* state [29]. In this case,126

the parent complex [Ru(phen)2(dppz)]2+ showed in 355 nm spectra a depen-127

dence of peak intensity upon pulse power; the probed state was assigned due128

to the resemblance of the spectrum to a superimposition of phz and phen129

spectra to the 1π, π* state, and the power dependence was attributed to rapid130

deactivation to 3π, π* with some crossover to MLCT, because some vibra-131

tional bands were shifted to lower frequency. Using [Ru(phen)2(dppzF2)]2+132

and [Os(phen)2(dppz)]2+ it was possible to examine the excited state con-133

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Figure 4: Resonance Raman spectra of [Ru(tbbpy)2(dppzBr2)]2+ in MeCN with three

different excitation wavelengths. Resonance Raman (458 nm) spectrum of [Ru(tbbpy)3]2+

in DCM is shown for comparison. Figure from Schafer et al. [23].

version. The MLCT energy is lower for these compounds and their transient134

resonance Raman spectra show no dependence of intensity upon power, sug-135

gesting only the 1π, π* state is observed and the MLCT state populated via136

3π, π* is not observed due to low ε at the probe wavelength[29].137

Time-resolved infra-red spectroscopy (TRIR) of [Re(CO)3(py)(dppzF2)]+138

shows IL π, π* in MeCN, while in H2O or D2O a second species, assigned as139

MLCT(phz) based on λabs and τ , is also observed [30]. On the ps timescale,140

[Re(CO)3(py)(dppzF2)]+ in MeCN spectrally resembles the π, π* ‘marker’,141

with ν(CO) shifted to slightly lower frequencies (2031, 1930 cm-1) than the142

ground state (2037, 1934 cm-1). Spectra recorded on the ns timescale shows143

a mixed π, π* (2031, 1930 cm-1)/MLCT(phz) state. The MLCT state shows144

a large upshift in ν(CO) band positions to 2120, 2057, 2014 cm-1, indicat-145

ing electron density is localised away from the CO groups and there is little146

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backbonding. In H2O and D2O the mixed π, π*/MLCT(phz) state (ν(CO)147

shifted from 2036, 1935 cm-1 in the ground state to 2029, 1924 cm-1 (π, π*)148

and 2108, 2047, 2003 cm-1 (MLCT(phz)) is formed on the ps timescale, show-149

ing that the solvent influences the formation of the equilibrium and excited150

state decay rate [30].151

Singly substituted compounds are expected to show the same effect as152

disubstituted ones, only to a lesser extent as the overall electron-withdrawing153

effect is reduced. Ered values are expected to be more positive than dppz but154

more negative than the equivalent dppzX2, and λem and λabs are expected155

to red shift relative to dppz. For example the lowest energy absorption band156

for dppzBr lies at 385 nm while for dppzBr2 is observed at 392 nm[23] and157

the ligand dppzCl has Ered (in DMF) of -1.53 V [21], compared to -1.64 V158

for dppz and -1.42 V for dppzCl2.159

In addition to halogens, many other electron-withdrawing groups have160

been substituted at the dppz E-ring (Figure 1), such as NO2, CN and CF3.161

These show the same effects as the halogens; Ered more positive than dppz162

and red-shifted absorption (see Tables 1 and 2). For dppz(NO2)2 in DCM163

the lowest energy transition is at 388 nm (ε = 0.61×104 M−1 cm−1) in DCM,164

DMF and MeCN, which is likely broad due to a large number of transitions165

theoretically predicted [9, 19, 15]. This ligand emits at 513 nm with Φ =166

0.0467 in DMF [13]. For [Re(CO)3Cl(dppz(CF3)2)] the Ered is more positive167

than that of dppz at -1.05 V (vs Fc+/Fc) [17]. For the monosubstituted free168

ligand dppz(CF3) in DMF Ered is similar to dppz (-1.38, -2.14 V (vs Fc+/Fc)),169

with a red shifted absorption (see Table 2), and an emission spectrum similar170

to dppz(NO2) (λem = 521 nm, Φ = 0.005).171

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The ligand dppz(CN) shows absorption bands red-shifted and with lower172

ε relative to dppz and emits at 438 nm (Φ = 0.002) in DCM [15, 21], while173

[Ru(bpy)2(dppz(CN))]2+ emits at 681 nm with Φ = 0.002. For the Ru com-174

plex Eox is 1.24 V (Ru(II) → Ru(III)) and Ered is -0.75 V vs SCE [21].175

[Ru(bpy)2(dppz(CN)2)]2+ shows Ered of -0.54, -1.12 V which is more pos-176

itive than for the singly substituted analogue [20]; however both of these177

ligands show the effect of the CN group extending conjugation of the phz178

MO through further lowering of the LUMO [20].179

Dppz ligands with COOH/COOR substituents at the 11 position show180

normal electron-withdrawing group behaviour (see Tables 1 and 2). However181

their complexes have emissive properties that are sensitive to solvent - the182

[Ru(phen)2(dppz−COOH)]2+ complex emits at 606 nm in water with rela-183

tive intensity of 0.012 compared to 10 µM [Ru(bpy)3]2+ in aqueous solution,184

and at 612 nm in MeCNwith 0.878 relative intensity compared to the same185

standard. For the related [Ru(phen)2(dppz−COOPh)]2+, which no longer186

has the hydrogen available to interact with solvent, emission is observed at187

612 nm in water, with relative intensity of 0.01, and 660 nm in MeCN (rela-188

tive intensity 0.034). This indicates an increase in solvatochromic behaviour189

but a decrease in the difference in quantum yield values when H→Ph [26].190

Studies on dppz-COOEt report a ligand-centered Franck-Condon state as-191

signed by resonance Raman spectroscopy, and LC(phz) THEXI state which192

is calculated and is consistent with experiments [24, 16]. The [Re(CO)3Cl]193

complex shows a MLCT(phz) excited state on the ps timescale as determined194

by TRIR; the nature of the MO populated is determined by the magnitude195

of the shift in ν(CO) [31].196

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N N

N

X

Y

X=Y=Br X=Br, Y=H X=CH3, Y=HX=Cbz, Y=Br X=Y=Cbz

N

N N

N

S

S

S

SS

S

N

= Cbz= dppzTTF

10,13-dppzBr210-dppzBr10-dppzMedppz(Cbz)(Br)dppz(Cbz)2

Figure 5: Substituents at other phenazine positions. Compounds discussed in some detail

in the text are shown in bold.

The dppz ligand has also been substituted at the 11-position with an oxa-197

diazole group [16]. Electrochemical studies show an oxidation of the oxadia-198

zole (1.69 V) and normal Ered of the phz MO (see Table 1). Absorption bands199

are observed at 400 nm, which is a longer wavelength than other electron-200

withdrawing substituents and is attributed to the extension of conjugation.201

Emission is reported at 427 nm with Φ = 0.04. DFT calculations are used202

to assign vibrational modes, and resonance Raman spectra at 356 nm show203

a ligand-centered π, π* chromophore for dppz(oxa) and the Cu complex; the204

Re complex shows LC and MLCT(phen), which becomes more dominant at205

longer wavelengths, while the Ru(bpy)22+ complex shows MLCT(bpy) at206

this wavelength [21].207

In summary, many different electron-withdrawing substituents have been208

reported at the 11 and/or 12 position of dppz, which affect the phenazine209

part of this molecule. This is shown by Ered being more positive than in210

dppz (see Table 1) and a red shift in absorption spectra (see Table 2) which211

is greater when the group also extends conjugation (CN, oxa). The effect on212

emission is harder to predict and varies more with solvent.213

The 10,13 substitution pattern has also been studied in dppz ligands (see214

Figure 5), for example 10,13-dppzBr2 and Re(CO)3Cl(dppzBr2) [28]. The215

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N N

N

X

Y

X=Y=BrX=Y=MeX=Y=Phac

N

N N

N

Y

X

X=Y=NH2X=Y=Cl

2,7-dppzBr22,7-dppzMe22,7-dppz(Phac)2

3,6-dppz(NH2)23,6-dppzCl2

Figure 6: Substituents at other phenanthroline positions. Compounds discussed in some

detail in the text are shown in bold.

electronic absorption spectrum of the ligand is slightly red-shifted compared216

to unsubstituted dppz. Complexation to Re causes a further red-shift, and217

the appearance of a low-energy MLCT (around 400 nm), which in this case is218

very weak. Emission in DCM is red-shifted by the Br substituents to 560 nm,219

consistent with lowering in energy of the π*(phz) MO. Emission of the com-220

plex (from the MLCT state) is red shifted relative to both Re(CO)3Cl(dppz)221

and 10,13-Br-dppz and is observed at 582 nm (Φ = 0.57 in degassed CH2Cl2).222

In this case, altering the position of electron-withdrawing phz substitution223

does not have a different effect on the electronic properties, which are again224

all influenced by the lowering in energy of the phz MO.225

Electron withdrawing substituents at the phenanthroline moiety (rings A226

and C, Figure 1) have also been reported [32]. Substitution of phenanthroline227

with Br at the 2 and 7 positions does not perturb the physical structure (bond228

lengths etc) of dppz[32]. FT-Raman spectra show changes in pyridine ring-229

breathing modes upon Br substitution, and phenanthroline-based vibrations230

show band changes upon complexation to [Ru(tbbpy)2]2+ [32]. Calculated231

spectra match with experimental spectra, and model band shifts due to sub-232

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stitution accurately. The bands that shift significantly upon Br substitution233

are predicted to be those with large phen displacement, as may be expected,234

while highly delocalised dppz modes shift to a smaller extent[32]. Additional235

studies show that the electronic absorption band above 330 nm is shown to236

be unchanged relative to the unsubstituted dppz complex, while the MLCT237

band is resolved into two bands. Resonance Raman spectroscopy showed238

enhancement of tbbpy bands with higher energy excitation, and dppz bands239

with lower energy excitation, hence substitution at the phen MO shifts the240

Ru→dppz MLCT to lower energy while not affecting the Ru→tbbpy MLCT241

transitions, whereas when there is no substituent these overlap and only one242

band is observed [33]. The electronic absorption spectrum of 3,6-dppzCl2 in243

DMSO red-shifts only slightly relative to dppz [34].244

2.2. Electron-donating substituents245

Electron-donor substituents reported in the literature give more negative246

Ered values than for dppz; the phz MO becomes more difficult to reduce as247

it is raised in energy, however electronic absorption spectra still show a red248

shift.249

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Table 3: Electrochemical data for electron donating substituents. Compounds discussed

in some detail in the text are shown in bold. 11,12-substitution pattern unless stipulated

otherwise.

Ligand Eox Ered Solvent Standard electrode Reference

dppz -1.34 DCM Fc/Fc+ [12]

-1.64, -2.26 DMF Fc/Fc+ [13]

-1.28 DCM SCE [14]

dppzMe2 -1.14 DMF Ag/AgCl [15]

-1.71, -2.56 DMF Fc/Fc+ [11]

2,7-dppzMe2 -1.76 DMF Fc/Fc+ [35]

dppzMe -1.18, -1.88 DMF SCE [10]

-1.30 DCM SCE [9]

10-dppzMe -1.40 DCM Fc/Fc+ [12]

dppzOMe -1.50 DCM Fc/Fc+ [12]

dppz(NH2)2 -2.04 DCM Fc/Fc+ [18]

dppz(NH2) -1.35, -1.73 DMF SCE [10]

-1.85, -2.57 DMF Fc/Fc+ [13]

-1.87 DCM Fc/Fc+ [18]

dppz(CH2Br)2 decomposed [18]

dppzTTF 0.29, 0.64 -1.61 DCM Fc/Fc+ [36]

dppz-TTF-dppz 0.73, 1.08 -1.17 DCM Ag/AgCl [37, 38]

dppz(SCN)2 -0.85 DCM SCE [14]

dppz(S2CS) -0.98 DCM SCE [14]

dppz(Sdec)2 -1.23 DCM SCE [14]

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Table 4: Electronic absorption and emission data for electron donating substituents. Com-

pounds discussed in some detail in the text are shown in bold.

Ligand λabs (ε×104 M−1

cm−1)

λem (Φ) Solvent Reference

dppz 290 (2.5), 340 (0.9),

350 (1.0), 359 (1.3),

367 (1.2), 379 (1.4)

DMF [11]

270 (4.37), 367

(1.13), 379 (1.29)

DCM [9]

dppzMe2 274 (6.11), 347

(0.75), 355 (0.945),

366 (1.39), 374

(1.22), 386 (1.82)

DCM [15]

386 (1.82) 415 (0.012) [22]

300 , 344, 352, 360,

369, 379, 390

DMF [11]

dppzMe 274, 366, 385 CHCl3 [10]

273 (4.70), 365

(1.05), 385 (1.22)

DCM [9]

232, 287, 372 DCM [39]

10-dppzMe 276 (3.05), 300

(sh), 361 (0.676),

380 (0.667)

533 DCM [12]

dppzOMe 275 (5.27), 382

(1.16), 400 (1.43)

522 DCM [12]

422 (0.03) DCM [25]

dppz(NH2)2 229 (5.81), 262

(3.97), 276 (4.26),

291 (4.52), 308

(4.90), 396 (1.55),

442 (2.62)

DCM [18]

3,6-

dppz(NH2)2

283 (4.17), 306

(3.63), 340 (sh),

350 (1.51), 400

(sh), 422 (1.94)

DMSO [34]

277, 299, 344, 408 MeOH [34]


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dppz(NH2) 292, 425, 430 CHCl3 [10]

293 (6.9), 308 (7.0),

447 (2.6)

558 (1.07×10-3) DMF [13]

240 (2.86), 290

(3.14), 304 (3.03),

438 (0.97)

534 (0.24) MeCN [40]

428 517 (0.24) DCM [40]

454 555 (0.17) DMF [40]

452 565 (0.09) EtOH [40]

238 (7.48), 251

(6.57), 293 (6.94),

308 (7.02), 447

(2.61)

DCM [18]

dppz(CH2Br)2 247 (4.48), 253

(4.16), 287 (4.37),

293 (4.55), 303

(3.98), 378 (1.27),

390 (1.91)

DCM [18]

dppz(Ph)2 374, 394 433 DCM [23]

dppz(Ph−Ph)2 233, 297, 408 470 DCM [23]

dppz(Ph−tBu)2 229, 286, 406 455 DCM [23]

dppzTTF 518 864 DMF [37]

523 859 acetone [37]

535 820 DCM [37]

527 788 THF [37]

547 798 CHCl3 [37]

537 708 toluene [37]

539 622 cyclohexane [37]

dppz-TTF-

dppz

530 634 toluene [41]

530 675 CHCl3 [41]

525 751 DMF [41]

[Ru(bpy)2(dppz

Ph(NH2)2)]2+

260, 310, 410 627 MeCN [42]

260, 310, 410 653 DMF [42]

260, 310, 410 636 DMSO [42]


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[Ru(phen)2(dppz

Ph(NH2)2)]2+

649 MeCN [42]

660 DMF [42]

620 DMSO [42]

dppz(SCN)2 287 (5.24), 381

(1.72), 401 (1.97)

DCM [14]

dppz(S2CS) 290 (3.59), 386

(1.02), 407 (1.34),

427 (1.11)

DCM [14]

dppz(Sdec)2 293 (4.99), 409

(1.35), 434 (2.04)

DCM [14]

dppz(Cbz)(Br)258, 290, 335 594 DCM [28]

dppz(Cbz)2 258, 290, 335 624 DCM [28]

For dppzMe2 and dppzOMe2; Ered values are more negative than250

those of dppz (-1.14, -1.25 and -1.06 V respectively) in DMF [15].251

[Ru(bpy)2(dppzMe2)]2+ has first and second reduction potentials of -252

0.77 V (dppz-based) and -1.13 V (bpy-based) in MeCN [43]. Electronic253

absorption spectra in DCM and DMF are similar to that for dppz with254

respect to λ and ε, with LC π, π* transitions in the 360-370 nm range255

and above 300 nm [11, 15]. The dppzMe2 ligand has also been reported256

complexed with Ru(bpy)22+ [11] and Re(CO)3Cl [17]. Using TRIR,257

[Re(CO)3(py)(dppzMe2)]+ is shown to populate a π, π* state on the ps scale258

in MeCN which decays to a π, π*/MLCT(phz) equilibrium more slowly259

than for the dppzF2 complex, and in H2O shows a π, π* state on the ps260

scale also [30]; this is consistent with the observation that less electron-261

withdrawing groups show π, π* and MLCT(phen) excited states [17]. For262

[Ru(bpy)2(dppzMe2)]2+ Eox = 1.58 V (Ru(II) to Ru(III)) and two reduction263

processes (-0.77, -1.13 V in MeCN) are observed. The first reduction is264

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assigned to the dppz ligand, while the second reduction is of a bipyridine265

ligand[43]. Electronic absorption bands at 286 and 381 nm are assigned266

to π, π* transitions, while the 446 nm band is MLCT in nature. Variable267

temperature emission in a study similar to that of Brennaman et al showed268

the same roll–over behaviour (approx 300 K) indicating an equilibrium269

between multiple 3MLCT states (bright and dark) as well as Ru d-d states270

[43].271

As for electron-withdrawing substituents, the singly substituted ana-272

logues are no longer symmetrical but show similar behaviour to the273

disubstituted systems but with a reduced effect. Electronic absorption274

bands for dppzMe are similar in position to those of dppzMe2, but show275

lower ε [10, 9, 39], see Table 4. The Ered of dppzMe (-1.30 V vs SCE in276

DCM) is also lower than that of dppz [10, 9]. For dppzOMe, Ered values277

show OMe to be a stronger donor than Me (-1.50 V in DCM)[12]. Electronic278

absorption spectra are normal, with bands observed at 382 and 400 nm in279

DCM, red-shifted and with lower ε relative to dppz [12]. Methyl substitution280

at the 10-position rather than the 11-position does not have a significant281

effect on the properties [12].282

Both dppz(NH2)2 and dppzNH2 are reported to have Ered values more283

negative than that of dppz, consistent with their electron-donating effect284

(see Table 3). Also in both of these ligands, there is a significant red-shift285

in electronic absorption bands and changes in ε attributed to an increase in286

conjugation due to the lone pair on the nitrogen [18]. This increases electron287

density at the phz MO which is involved in the lowest energy π, π* transition288

[18]. The disubstituted analogue shows a slightly lower energy absorption289

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band. The compounds are emissive and show solvatochromism [18].290

Aromatic substituents are also expected to extend the conjugation and291

thus lower the phz MO energy, and being large π systems this effect should292

be much greater than that for NH2. For dppz(Ph)2, dppz(C6H4−Ph)2 and293

dppz(C6H4−tBu)2 [23] there is an increasing red-shift in the lowest energy294

absorption band in the order Ph<C6H4-tBu<C6H4-Ph, which corresponds295

to the increase in conjugation. This lowering of excited state energy is also296

observed in the emission spectra, with a red-shift in emission maxima in the297

same order (Ph = 433 nm, C6H4-tBu = 455 nm and C6H4-Ph = 470 nm).298

Substitution with phenylacetylene groups at the 11, 12 positions perturbs the299

dppz symmetry due to steric interactions inducing torsion about the C≡C300

bonds in opposite directions [32].301

A strong electron-donating group that has been widely utilised in the field302

of molecular electronics due to its charge transfer characteristics is tetrathio-303

fulvalene (TTF). Addition of TTF to the phz ring of dppz (see Figure 6)304

changes the lowest energy transition from π, π* to ILCT TTF→dppz. For305

a series of [Ru(bpy)3-n(dppzTTF)n]2+ complexes (n=1-3), TTF undergoes306

two one-electron oxidation steps [37]. The ligand exhibits Eox = 0.29, 0.64307

V and Ered = -1.61 V in DCM vs Fc/Fc+, which is slightly more negative308

than that of dppz [36]. The lowest energy transition (ILCT) is observed at309

significantly longer wavelength than for other dppz derivatives, ranging from310

518 nm in DMF to 539 nm in cyclohexane. Emission is also observed at 864311

nm in DMF to 622 nm in cyclohexane [37]. The oxidised ligand (dppzTTF+)312

is observed using spectroelectrochemistry and TD-DFT calculations to have313

a dppz→TTF transition as the lowest energy, while the reduced ligand is314

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shown to be populated on the phenazine section [37]. The same electrochem-315

ical and electronic absorption band values are reported when coordinated to316

an Fe centre [38]. The fused dppz-TTF-dppz system exhibits significant sol-317

vatochromism of the emissive state, with λem maxima at 634 nm in toluene,318

675 nm in chloroform and 751 nm in DMF; λabs maxima ranged from 530 to319

525 nm in these solvents [41].320

As with electron-withdrawing substituents, the phenanthroline moiety321

can also be substituted to alter electronic properties, although as the lowest322

energy unoccupied MO tends to be phz-based, this may be more likely to323

affect metal binding. The Ered for 2,7-dppzMe2 is -1.76 V in DMF, which is324

similar to that of unsubstituted dppz, indicating it is likely phz is still the325

lowest energy MO [35]. The dppz substituted with NH2 groups at the 3 and326

6 positions[34] shows a different electronic absorption spectrum to dppz in327

DMSO, red shifting and changing in shape (see Table 4); this has been shown328

to be unaffected by concentration and therefore not attributed to dimerisa-329

tion. The spectral band shape in MeOH did not change in structure, but did330

exhibit a blue-shift (λ = 277, 299, 344, 408 nm), indicating solvent-solute in-331

teractions were not the cause of the spectral pattern. Phenylacetylene groups332

at the 2 and 7 positions extend the phenanthroline conjugation and cause333

large changes in bond length at the phen moiety [32], but maintain the sym-334

metry of the ligand; DFT calculations are consistent with crystal structures335

in this respect. The increased polarisability due to the extension of the π336

system leads to more intense Raman modes, and these intense modes are337

assigned to phen vibrations [32].338

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2.3. Intra-ligand charge-transfer systems339

Using sulfur substituents (both electron withdrawing SCN and electron340

donating Sdec and S2CS) at the 11,12 positions of dppz produces ligands with341

unusual optical properties [14]. Ered values are reported in DCM to be -0.85,342

-0.98 and -1.23 V for dppz(SCN)2, dppzS2CS and dppz(Sdec)2 respectively,343

all of which are more positive than that of unsubstituted dppz; the same344

trend is observed for Re complexes.345

In all cases, substitution also causes a red-shift in electronic absorption346

bands, consistent with the LUMO energy being lowered, and this effect347

is greater for S2CS and Sdec than SCN (lowest energy 427 nm, 434 nm348

and 401 nm respectively, and ε 1.11, 2.04 and 1.97 ×104 M−1 cm−1, see349

Figure 7); this shifting is predicted by TD-DFT calculations. Re com-350

plexation causes the typical MLCT tailing in dppz(SCN)2, while for the351

electron-donating substituents a large increase in extinction coefficient of352

the lowest energy band is observed, as well as a red-shift and a new band353

at 330 nm. Resonance Raman spectroscopy and DFT calculations allow the354

assignment of the lowest energy transition in dppz(S2CS) and dppz(Sdec)2355

as S→phz, for [Re(CO)3Cl(dppz(SCN)2)] metal→dppz and for the other356

two complexes, a combination of metal→phen and S→phz. Resonance357

Raman spectra were consistent with this assignment and the nature of358

MO population predicted [14]. These ligands have also been studied as359

Cu(bpy(mes)2)+ complexes, along with the unsubstituted dppz equiva-360

lent - this shows MLCT(Cu→bpy(mes)2) and dppz π, π* transitions, and361

TD-DFT calculations predict a low ε MLCT(Cu→dppz) transition also [44].362

Strong bands in the visible region for the dppz(Sdec)2 and dppzS2CS Cu363

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Figure 7: Electronic absorption spectra for ligands (left) and complexes (right) reported

by Fraser et al [14].

complexes showed similar behaviour as for Re, with the enhancement of364

dppz and S2CS vibrational modes in resonance Raman spectra confirming365

the Cu→dppz and S→phz nature, with the enhancement of bpy bands to366

the red indicating a Cu→bpy(mes)2 transition[44].367

Carbazole-substituted dppzs (see Figure 5) which are sterically hindered368

to avoid triplet-triplet annihilation in OLEDs have been investigated [28].369

Dppz(Cbz)(Br) and dppz(Cbz)2 show electronic absorption bands at 258,370

290 and 335 nm in DCM attributed to carbazole π, π* transitions, as well371

as normal dppz π, π* transitions which are red shifted relative to dppz. Re372

complexation red shifts the spectra and the carbazole increases the extinction373

coefficient in the visible; however the MLCT is too weak to be observed374

[28]. The extended conjugation afforded by carbazole substituents causes375

a red-shift in emission maxima, observed at 594 and 624 nm in DCM for376

dppz(Cbz)(Br) and dppz(Cbz)2 respectively [28].377

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3. Triazole Ligands378

The development of ‘click’ chemistry has provided an effective way to379

synthesise a large range of N-donor ligands, in the form of triazoles. This is380

achieved through the use of the functional group tolerant Cu(I)-catalyzed381

1,3-cycloaddition of organic azides with terminal alkynes (the CuAAC382

reaction[45]). The triazole containing ligands can be synthesised to give383

a number of different mono-, bi- and tridentate ligands involving phenyl,384

pyridine, polypyridine, amide and other moieties.385

These ligands are almost always reported as complexes, with a wide range386

of metals utilised. Unsurprisingly these metals impart their own character-387

istic photophysics on the ligands so will need to be taken into account when388

discussing the various triazole ligand types. Where possible the Re com-389

plexes will be discussed first for a number of reasons, including: (1) They are390

highly studied because of a relatively robust synthetic chemistry; (2) The Re391

complexes generally exhibit a simple MLCT transition which is unaffected392

by the metal d-d orbitals which are relatively high in energy; (3) Ancillary393

ligands do not interact strongly, therefore reducing the risk of creating new394

chromophores and related photophysics which would complicate the Re tri-395

azole interaction. Copper complexes are also considered, however they tend396

to have short lifetimes and can be less photostable. Ruthenium complexes397

are of interest because of their potential utility, for example as chelators with398

DNA [46, 47]. The MLCT is perturbed by the ligand to a lesser extent than399

rhenium, additionally extra complexity is conferred by the interaction of the400

ligand with ancillary bpy moieties. Finally iridium has been used many times401

for making triazole complexes, again because of their potential utility, for402

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example as light-emitting diodes due to their phosphorescence[48, 49]. The403

iridium complexes exhibit a complicated photochemistry and rather than404

considering the ligand of interest the photophysics is usually dominated by405

the ancillary ppy ligands[50, 51]. Photophysical properties for selected rhe-406

nium(I) and ruthenium(II) complexes with triazole ligands are presented in407

Table 5.408

Table 5: Electronic absorption and emission data for selected rhenium(I) and ruthe-

nium(II) triazole compounds.

Compound λ / nm (ε / mM−1 cm−1) λem /

nm

φ ×

100

τ /

ns

Solvent Ref.

Re(CO)3Cl(pytriaC8H17) 273 (11.6), 288 (9.4), 333 (4.1) 532 1.2 121 MeCN [52]

Re(CO)3Cl(pytriaCH2Ph) 270 (12.3), 290 (9.5), 336 (3.9) 532, 538 1.2 103 MeCN [52, 53]

Re(CO)3Cl(pytriaCH2PhOMe) 272 (13), 290 (9.5), 333 (3.9) 532 1.3 79 MeCN [52]

Re(CO)3Cl(pytriaCH2PhNO2) 265 (22.6), 292 (12.7), 333 (4.2) 532 0.1 7 MeCN [52]

Re(CO)3Cl(pytriaPh) 278 (19.7), 330 (5.5) 532 3.6 162 MeCN [52]

Re(CO)3Cl(pytriaFc) 282 (17.3), 330 (5.6) 532 MeCN [52]

Re(CO)3Cl(pytriaPhOMe) 277 (39.3) 330 (6.5) 532 1.5 127 MeCN [52]

Re(CO)3Cl(pytriaPhNO2) 277 (50.3) 330 (11) 532 61 MeCN [52]

Re(CO)3Cl(pytriaGlc) 331(3.9) 538 MeCN [53]

Re(CO)3Cl(pytriaAcGlc) 332 (4.0) 530 MeCN [53]

[Ru(bpy)2(pytria−βCD)]2+ 610 0.6 24.8 Water [54]

[Ru(bpy)2(pytria−ada)]2+ 615 0.5 19.6 Water [54]

[Ru(bpy)2(pytriaCH3)]2+ 615 0.6 27.4 Water [54]

[Ir(ppy)2(pytria−βCD)]+ 475 54 2800 Water [54]

[Ir(ppy)2(pytria−ada)]+ 475 23 1000 Water [54]

[Ir(F2ppy)2(pytria−ada)]+ 450 16 1100 Water [54]

[Ru(dmbpy)2(pytriaC10H21)]2+ 260 (27.8) 286 (71.5) 413 (11.9), 451

(12.5)

575 DCM [55]

[Ru(dmbpy)(pytriaC10H21)2]2+ 273 (65.4), 286 (47.3), 361 (10) 393

(13.7)

563 DCM [55]

[Ru(pytriaC10H21)3]2+ 270 (61.2), 385 (15.6) DCM [55]

[Ru(dmbpy)2(pytriaC11H22OH)]2+ 261 (32.4), 286 (70.6), 380 (7.5), 418

(10.2)

DCM [55]

[Ru(pytrianap)3]2+ 272 (56.2), 295 (35.3) 385 (14.4) DCM [55]

[Ru(dmbpy)2(pytrianap)]2+ 260 (19.4), 286 (60.2), 430 (10.6) DCM [55]

[Ru(dmbpy)2(pytriaPhOMe)]2+ 260 (30.1), 285 (80.4), 417 (10.4) DCM [55]

[Ru(pytria−PS)3]2+ 383 (15.9) DMF [56]

[Ir(F2ppy)2(pytria−ada)]+ 248 (5.1), 302 (2.1) 362 (5.5) 453 21 680 DCM [57]

[Ir(F2ppy)2(pytriaCH2Ph)]+ 247(5.2), 302 (1.9), 363 (5.5) 452 15 730 DCM [57]

[Ir(F2ppy)2(pytriaPh)]+ 259 (7.7), 304 (3.3) 362 (8.7) 453 24 870 DCM [57]

[Ir(F2ppy)2(pytriaPh2)]+ 261 (3.9), 291 (3.9), 314 (2.7) 358 (6.1) 452 11 2240 DCM [57]

[Ir(ppy)2(pytriaC6H13)]2+ 256(37.9), 384(4.8), 411(3.7) 477 20 1700 THF [58]

[Ir(F2ppy)2(pytriaC6H13)]+ 249(37.5), 362(5.1), 387(3.7) 453 24 2000 THF [58]


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nm

φ ×

100

τ /

ns

Solvent Ref.

[Ru(dmbpy)2(H1)]2+ 594 0.1 DCM [59]

[Ru(dmbpy)2(H2)]2+ 647 2.2 DCM [59]

[Ru(dmbpy)2(H2)]2+ 286 (63.4), 328 (38.6), 441 (11.6) 674 0.1 MeCN [60]

[Ru(dmbpy)2(H3)]2+ 286 (103.9), 312 (51.6), 440 (18.3) 620 0.1 MeCN [60]

[Ru(dmbpy)2(H4)]2+ 286 (74.7), 341 (22.6), 442 (12.4) 640 0.2 MeCN [60]

[Ru(dmbpy)2(H5)]2+ 286 (125.6), 315 (60.9), 438 (20.6) 621 0.1 MeCN [60]

[Ru(dmbpy)2(H1)]2+ 286 (133.1), 333 (59.8), 435 (23.6) 602 0.1 MeCN [60]

[Ru(dmbpy)2(H6)]2+ 286 (76.9), 326 (52.5), 440 (12.8) 642 < 0.1 MeCN [60]

[Ru(dmbpy)2(H7)]2+ 286 (83.1), 316s (40.5), 442s (12.5) 610 0.3 MeCN [60]

[Ir(F2pMepy)2(pyCtriaCF3)] 366, 426 464 22 DCM [61]

[Ir(F2pMepy)2(MepyCtriaCF3)] 370, 424 456 39 3150 DCM [61]

[Ir(F2pMepy)2(MeOpyCtriaCF3)] 368, 424 456 25 3570 DCM [61]

[Ir((CF3)F2pMepy)2(pyCtriaCF3)] 352, 422 456 20 DCM [61]

[Ir((CF3)F2pMepy)2(MepyCtriaCF3)] 364, 416 448 42 3580 DCM [61]

[Ir((CF3)F2pMepy)2(MeOpyCtriaCF3)]372 459 DCM [61]

[Ir(F2p(Me2N)py)2(MeOpyCtriaCF3)] 364, 426 469 6 DCM [61]

Re(CO)3Cl(pyCH2triaPh) 251 (24.1), 286s (10) 538 15 MeCN [62]

Re(CO)3Cl(pyCH2triaPhNO2) 271s (21.5), 302 (22.8) MeCN [62]

Re(CO)3Cl(pyCH2triaPhOMe) 258 (34.4), 301s (11.5) 419, 524 10,

13

MeCN [62]

Re(CO)3Cl(pyCH2triaCH2Ph) 254 (13.1), 289s (6.6) 537 17 MeCN [62]

Re(CO)3Cl(pyCH2tria−caf) 266 (21.5), 299s (7.4) 526 13 MeCN [62]

Re(CO)3Cl(pyCH2tria−ster) 254 (14), 287s (8.8), 298s (6.6) 520 13 MeCN [62]

Re(CO)3(py(CH2triaPh)2) 250 (42), 264s (33), 288 (17) 613 0.14 62 MeCN [63]

Re(CO)3(py(CH2triaC3H7)2) 256 (19), 286 (7.0) 605 0.12 87 MeCN [63]

[Ru(py(triaPS)2)2]2+ 394 (16.7) DMF [56]

[Ru(tpy)(py(triaC10H21)2)]2+ 286 (42), 303 (39), 356 (5.5), 432 (11.5) 583 DCM [64]

[Ru(tpy)(py(triaC11H22OH)2)]2+ 287 (38), 305 (36), 356 (4.5), 435 (10) DCM [64]

[Ru(tpyPhBr)(py(triaC10H21)2)]2+ 287 (67), 356 (6.5), 438 (16), 456 (16.5) DCM [64]

[Ru(tpyPhBr)(py(triaC11H22OH)2)]2+ 287 (67), 356 (6.5), 438 (16), 456 (16.5) DCM [64]

[Ru(tpyPhBr)(py(triaPhOMe)2)]2+ 300 (73), 435 (13.5), 456 (14.5) DCM [64]

[Ru(tpyPhBr)(py(triaCH2PhBu)2)]2+ 288 (73), 357 (6.0), 435 (16.5), 455

(17.5)

DCM [64]

[Ru(py(triaC10H21)2)

(py(triaC11H22OH)2)]2+

256 (32.5), 286 (63), 395 (18) DCM [64]

[Ru(tpy)2]2+ 290 (40), 308 (38), 432 (10) 604 DCM [64]

[Ru(py(triaC10H21)2)2]2+ 226 (46), 255 (27), 285 (61), 394 (16) DCM [64]

[Ir(ppy)2(pytria−bCD)]+ 263(47.7), 355(9.5), 397(6.0), 440(3.0) 500 0.2 900 THF [58]

[Ir(F2ppy)2(pyCtriaC6F5)]+ 254(44.1), 346(9.1), 372(7.4), 427(1.3) 485 0.3 400 THF [58]

[Ir(ppy)2(pyCtriaF17]+ 262(47.3), 356(9.0), 396(5.6), 436(2.9) 492 0.7 1600 THF [58]

[Ir(ppy)2(pyCtria−mPhF)]+ 266(47.1), 359(8.3), 393(5.1), 432(2.6) 493 0.3 230 THF [58]

[Ir(ppy)2(pyCtriaC6F5)]+ 263(48.0), 355(8.8), 396(5.2), 429(3.2) 505 1.5 1900 THF [58]

Re(bpy)(CO)3(MetriaPh) 266, 298, 337 543 482 DCM [65]

Re(bpy)(CO)3(PrtriaPh) 266, 298 338 552 475 DCM [65]

Re(bpy)(CO)3(PhCH2triaPh) 265, 301, 339 535 513 DCM [65]

Re(bpy)(CO)3(PrtriaPhMe) 265, 300, 346 542 - DCM [65]

[Ru(tpy)φ(triaBun)2]2+ 367(14.0), 490(10.0), 537(8.0) MeCN [66]

[Ru(tpy)φ(triaPh)2]2+ 378(21.0), 485(8.0), 524(7.0) MeCN [66]

[Ru(tpy)φ(triaBr)2]2+ 369(13.0), 500(10.0), 548(7.0) MeCN [66]


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nm

φ ×

100

τ /

ns

Solvent Ref.

[Ir(PhtriaMe)2(pytriaMe)2]Cl 190 - 240, 290-350 ∼ 510 9.7 27.1 MeCN [67]

[Ir(Phtria−ada)2(pytria−ada)2]Cl 190 - 240, 290-350 ∼ 510 4.8 18.0 MeCN [67]

[Ir(PhtriaMe)2(pytriaβCD)2]Cl 190 - 240, 290-350 ∼ 510 25.4 34.1 MeCN [67]

[Ru(bitriaC6H13)3]2+ ∼ 240, ∼ 310 methanol [68]

[Cu(diphos)(L1)] 286 (31.7), 325 (24.8), 362 (18.5), 416

(9.5)

632, 658 0.6 570 THF [69]

[Cu(diphos)(L2)] 288 (23.4), 330 (17.6), 425 (6.8) 633, 662 0.3 350 THF [69]

[Cu(diphos)(L3)] 287 (21.4), 328 (16.4), 436 (4.6) 633, 667 0.04 70 THF [69]

[Cu(diphos)(L4)] 289 (20.6), 321 (15.6), 378 (15.6), 419

(5.2)

631, 649 1.0 750 THF [69]

[Cu(diphos)(L5)] 284 (33.2), 330 (16.2), 416 (1.0) 631, 649 1.3 2000 THF [69]

[Cu(diphos)(L6)] 290 (22.3), 328 (11.7), 419 (8.4), 440

(6.5)

632, 658 0.15 60 THF [69]

[Ru(bpy)2(pytriaPh(OMe)2)]+ 290 (80.7), 485 (10.7) 685 110 MeCN [70]

[Ru2(bpy)4(pytria2Ph(OMe)2)]2+ 290 (148), 481 (18.9) 683 105 MeCN [70]

[Ru(bpy)2(pytria)]+ 465 (11.0) 650 145 MeCN [70]

[Ru2(bpy)4(pytriapy)]3+ 453 (22.6) 648 100 MeCN [70]

3.1. Pyridyl Triazoles409

3.1.1. Substitution on the Triazole410

Many studies have been reported in which the triazole is appended with411

a number of different functional groups. A systematic study of the effect412

of changing the functional group attached to the “regular” type pyridine-413

triazole (pytriaR) ligand (where the substituent is appended at the N1 posi-414

tion) in a Re(CO)3Cl complex, was undertaken (Figure 8)[52].415

Very little perturbation is seen in the electronic absorption spectra of the416

complexes with different substitution of the R group (Figure 9). An MLCT417

band is consistently observed at between 330 and 336 nm while π, π* tran-418

sitions are observed at 265 to 290 nm. Despite the similarity in the position419

of the MLCT transition, DFT calculations suggest that its nature is quite420

different in the complexes with an insulating CH2 group in the substituent421

(such as pytriaCH2Ph) compared to those without (such as pytriaPh). While422

both transition types originate from the H-1 MO (a d-π orbital) the insu-423

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Figure 8: The structures of some “regular” type pyridine triazole ligand containing com-

plexes. Adapted from ref [52].

lated types terminate on the LUMO (based on the pytria moiety) while the424

conjugated types terminate on the L+1 (based on the triaR moiety). This425

result can be tested experimentally through the use of resonance Raman426

spectroscopy (Figure 10) which in fact does corroborate the computational427

results. While the Raman spectra obtained in resonance with the MLCT428

band look almost identical in the case of the insulated ligands with bands at429

1285, 1571, 1587 and 1625 cm−1 (because the HOMOs and LUMOs are not430

greatly perturbed with substitution at the triazole) those of the conjugated431

types display bands related to the specific R groups, notably the NO2 band432

at 1353 cm−1 (because the L+1 MO is based on the triaR unit).433

The emission behaviour of the series shows some perturbation with dif-434

ferent R groups, all exhibit a weak (quantum yield between 0.001 and 0.036)435

emission peak at 532 nm. The lifetimes show a dependence on R following436

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0.0

1.0

2.0

3.0

4.0

5.0- C

8H

17

- CH2Ph

- CH2PhOMe

- CH2PhNO

2

- Fc1

- Ph1

- PhOMe1

- PhNOε/

104

L m

ol-1

cm-1

R =2

250 300 350 400 450 500

Wavelength / nm

Figure 9: Electronic absorption spectra of Re(pytriaR)(CO)3Cl complexes shown in Figure

8. Reproduced with permission from ref [52].

1625

157112

85

C8H17

CH2PhOMe

CH2Ph

Ra

ma

nSIn

tens

ityS/S

a.u

1515

1522

1587

Ph

CH2PhNO

2

1508

1601

1353

PhOMe

Fc

1200 1300 1500 1600

PhNO2

RamanSShiftS/Scm-1

Figure 10: Resonance Raman spectra of Re(pytriaR)(CO)3Cl complexes shown in Figure

8. Reproduced with permission from ref [52]

the trend described for the MLCT transition above. That is, the insulated437

substituent types consistently have lifetimes around 55 ns shorter than the438

analogous conjugated ones (which are themselves ca. 60 - 160 ns, room439

temperature (RT) in MeCN)440

Electrochemistry returns equivalent results for all complexes in the series441

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except in the case of reduction for those containing a PhNO2 functional442

group. The oxidation of ReI/ReII occurs at 1.49-1.53 V versus SCE and is443

irreversible. Reduction of the triazole is also irreversible and occurs at -1.66444

- -1.74 V while that of the PhNO2 involves two processes the first reversible,445

the second irreversible, both based on the nitro group. The electrochemical446

data for a series of selected triazole complexes are shown in Table 6.447

The effect of benzyl and glycine substituents on pytriaR ligands in rhe-448

nium(I) complexes (Figure 8) has been investigated[53]. The optical absorp-449

tion and emission properties are virtually indistinguishable between these450

complexes indicating little perturbation by the substituents.451

The ruthenium complexes can include either one, two or three pytriaR452

ligands with any remaining ligands usually being bpy units. The poten-453

tial tuning of the triazole unit was investigated [54] with complexes of the454

type [Ru(bpy)2(pytriaR)]2+ where R = methyl, adamantane (ada) and β-455

cyclodextrin (βCD). The absorption spectrum is complicated somewhat by456

the inclusion of two different ligands lying at similar energies (Figure 11).457

From comparison to the simple [Ru(bpy)3]2+ spectrum the bands involving458

pytriaR can be assigned, these include the shoulder at 280 nm (π, π*) and459

the spread of MLCT bands at 400-500 nm ([Ru(bpy)3]2+ has a clear max-460

imum at 452 nm). The differing triazole functionalisation appears to have461

little effect on the observed absorption properties for these complexes in the462

400-500 nm region.463

Emission spectroscopy confirms the insulating nature of the triazole with464

λem at 610 nm for R=βCD and 615 nm for the others. Quantum yields range465

from 0.0047 to 0.0062 and lifetimes from 19 to 27 ns in water equilibrated466

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Figure 11: Electronic absorption spectra of [Ru(bpy)2(pytriaR)]Cl2 where R = CH3

(dashed), ada (dotted) and βCD (solid). Reproduced with permission from ref [54].

both with air and also with argon. These properties are consistent with467

a LUMO based on the (lower energy - less electron density) bpy ligand.468

Additionally, the low emission efficiency is explained by the smaller ligand469

field for the pytria-R causing a lowering of the metal triplet states (3MC)470

and subsequent depopulation of the 3MLCT state through these efficient471

non-radiative channels[71]. Transient absorption spectroscopy confirmed the472

involvement of the bpy moiety in the MLCT by identifying the bpy.− radical473

at 380 nm.474

The effect of chelating different numbers of pytriaR ligands was reported475

by Happ et al.[55] using the series [Ru(dmbpy)3-n(pytriaR)n](PF6)2. Imme-476

diately from the absorption spectrum (Figure 12) it is obvious that this has a477

significant effect on the electronic properties. A blue shift in the MLCT band478

(and to a lesser extent, the LC band) occurs as n is increased from 0 to 3 (from479

461 to 384 nm). The homoleptic systems are shown to be sensitive to their co-480

ordination geometry, for example the complex [Ru(pytrianap)3](PF6)2 shows481

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a shift in the MLCT maximum, fac: λabs,max = 385 nm, mer: λabs,max = 367482

nm. Again, tuning the triazole N1 substituent made little difference to the483

electronic absorption spectroscopy.484

Figure 12: Electronic absorption spectra of [Ru(dmbpy)3-n(pytriaC10H21)n](PF6)2 in

DCM where n = 0 (solid grey), n=1 (dashed), n=2 (dotted) and n=3 (solid black). Re-

produced with permission from ref [55].

The emission spectra (at 77 K) exhibit the same blue-shift trend as the485

absorption, from 592 nm (n=0) to 563 nm (n=2) where R=C10H21 (no emis-486

sion is observed for n=3). At room temperature no emission was observed487

from any of the complexes. Cyclic voltammetry confirmed the trend de-488

scribed above, that is, as n increases the HOMO (πmetal (t2g)) is slightly489

stabilised and the LUMO (π*) is destabilised leading to an increased band490

gap, a blue-shift. The LUMO is shown to be unaffected by substitution,491

indicating a LUMO based on the dmbpy as expected, however the HOMO is492

stabilised from R=C10H21 to R=naphthylen−1−yl (∼0.1 eV).493

The homoleptic Ru series [Ru(pytriaR)3](PF6)2[56] with R = Bn and494

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polystyrene (PS) show that R makes little difference to the electronic prop-495

erties (with the MLCT transition lying at 383 nm).496

Heteroleptic Ir complexes of the form [Ir(F2ppy)2(pytriaR)](PF6) (F2ppy497

= (2,4-difluoro)phenylpyridine)[57] where R = Bn, Ph and Ph2 (biphenyl)498

show absorption spectra that are similar for all substituents. These include499

π, π* transitions at ∼250 nm localized on the F2ppy and triazole moieties and500

∼300 nm based on the pyridine unit. The broad band around 370 nm is due501

to a 1MLCT and that at lower energy to a 3MLCT. One exception is observed502

where R = Ph2, in this case a π, π* transition based on Ph2 is observed at503

290 nm. The emission spectra of the iridium complexes (in DCM) are more504

structured, showing bands at 452, 483 and 505 nm, due to the significant505

3LC character of the excited state. Lifetimes and quantum yields of these506

complexes are similar (0.68 - 0.87 µs and 0.15 - 0.24 respectively) except in507

the case of R = Ph2 where τ = 2.2 µs and Φ = 0.1. The authors attribute508

this to the lowering of the LUMO (where R = Ph2) and subsequent increased509

mixing of the 3MLCT and 3LC states. The more LC excited state is lower510

energy (giving longer τ) while the Ph2 moiety would affect the non-radiative511

decay pathways, reducing the emission quantum yield. Cyclic voltammetry512

reveals oxidations occur at ∼1.23 eV while two reductions are seen at ca. -2.1513

eV (based on the pyridine ring of the ancillary ligand) and -2.5 eV (based on514

the F2ppy).515

The case where R = methyl, adamantane (ada) and βCD for similar516

complexes, of the form [Ir(ppy)2(pytriaR)]Cl[54] the absorption spectra and517

nature of transitions is unchanged with both the exclusion of the fluorines518

on the ancillary ppy ligands and the change in R (although the fluorines519

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do decrease the extinction coefficient). Substitution of fluorine by hydrogen520

leads to an increase of the HOMO energy and a red-shift of λem to 475521

nm. The lifetimes and quantum yields (in H2O) are similar to the F2ppy522

containing complexes above (0.4-0.7 ns and 0.2-0.5), R=βCD has the longest523

lifetime and greatest emission intensity, which the authors attribute to the524

shielding effect of the bulky βCD.525

TD-DFT has been used[58] to investigate the nature of the HOMO and526

LUMO for [Ir(ppy)2(trpy)] (where trpy = 2-1H-[1,2,3]trizol-4-ylpyridine).527

The transitions were described as a mixture of the iridium d orbitals and528

π orbitals of the two ppy phenyl groups and the π* orbital of the pytria lig-529

and respectively. This means the low lying absorption is a mixture of both530

3MLCT and 3LLCT.531

It is clear that the iridium complexes show utility in being able to tune532

the lifetime and quantum yield through substitution on the triazole while at533

the same time being able to tune the emission wavelength by substitution on534

the phenyl pyridine ancillary ligands.535

3.1.2. Substitution on the Pyridine536

In contrast to the striking lack of effect on properties when the triazole537

moiety is substituted at N1, substituents on the pyridine affect the electronic538

properties of the molecule markedly. The electronic properties for a series of539

[Ru(dmbpy)2(Hx)](PF6)2 complexes (x= 1 – 7, Figure 13) have been inves-540

tigated [59, 60].541

The electronic absorption spectra of these systems show a transition at542

300-400 nm that is dependent on the nature of R1 and R2. This is as-543

signed to an intraligand (IL) transition. The emission spectra of these com-544

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Figure 13: [Ru(dmbpy)2(Hx)](PF6)2 complexes (x = 1 - 7)[59, 60] showing the different

substitution on the pyridine. Labeling system as used in reference [60].

pounds also vary with R. λem range from 602 nm ([Ru(dmbpy)2(H1)]2+) to545

621 nm (([Ru(dmbpy)2(H5)]2+)) to 640 and 674 nm (([Ru(dmbpy)2(H4)]2+)546

and ([Ru(dmbpy)2(H2)]2+)). The π* MO, located on the triazole, is likely547

stabilised with the introduction of electron withdrawing groups, hence the548

red-shift. In MeCN the quantum yields were found to not be dependent on549

R, all were 0.001 except for [Ru(dmbpy)2(H3)]2+ where Φ=0.002.550

TD-DFT calculations were employed to investigate how the electron551

donating/withdrawing nature of R affected the frontier molecular orbitals552

(FMOs). When R is electron donating (for example ([Ru(dmbpy)2(H1)]2+)553

the π MO on the ligand is destabilised and becomes the HOMO, whereas554

with an electron accepting group (i.e. [Ru(dmbpy)2(H2)]2+) the π MO is555

stabilised and the metal d orbitals become the HOMO. The LUMO orbital556

also shows this delicate tuning between a π* MO based on the Rpytria557

ligand (LUMO in [Ru(dmbpy)2(H2)]2+ due to stabilisation from the electron558

withdrawing R) and a π* MO based on the ancillary dmbpy ligands (LUMO559

in [Ru(dmbpy)2(H1)]2+ due to destabilisation of the Rpytria MO with an560

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electron accepting R). Consequently the band at around 440 nm is predicted561

to be MLCT in nature for [Ru(dmbpy)2(H2)]2+ but MLCT and LLCT in562

[Ru(dmbpy)2(H1)]2+.563

Figure 14: Iridium complexes used to investigate tuning of the pyridine moiety by Park

et al.[61]

The effect of tuning the pyridine was also investigated in iridium com-564

plexes of the form shown in Figure 14 by Park et al.[61] The absorption565

spectra are unchanged from the iridium complexes described in the preced-566

ing section (despite the change to a 1,2,4-triazole unit). For complexes of567

the type [Ir(F2pMepy)2(L)] substitution at the pyridine ring of the triazole568

ligand results in shifts from 366 to 370 nm. In the emission spectra the 0,0569

transition is observed to shift from 456 to 464 nm. With a CF3 substituent at570

the ancillary ligands (R2, Figure 14) the absorption bands are more sensitive571

to the triazole ligand, shifting from 352 to 372 nm. The emission spectra also572

shift from 448 to 459 nm. The emission quantum yields are greatly affected573

too with the electron donating group giving twice the intensity, which range574

from ∼0.2 to ∼0.4 regardless of R2.575

3.1.3. Different Triazole Configurations576

A number of different configurations are possible for triazole ligands con-577

taining pyridine and these can act as bi- or tridentate ligands. ‘Regular’-type578

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triazoles involve chelation through the N3 nitrogen whereas ‘inverse’-type579

ones can be defined as coordinating through the less electron rich N2 nitro-580

gen atom.

Figure 15: Inverse-type triazole ligands studied in reference [62]

581

The effect of the ‘inverse’-type triazole pyridine ligands in a Re complex582

has been reported (Figure 15)[62]. The electronic absorption spectra follow a583

similar trend to the ‘regular’-type ligands, but red-shifted. MLCT bands are584

observed at around 302-298 nm for R−−NO2Ph, MeOPh, imidazole or steroid585

and 286-289 nm where R−−Ph or Bn while π, π* bands occur at 250-270 nm,586

red shifting with electron donating R. The profile of the spectrum is compa-587

rable to the ‘regular’-type pytriaR complexes except when R−−NO2Ph when588

the band at 302 nm becomes slightly more intense than the LC band. This589

is predicted by TD-DFT which also describes the transition as MLCT with590

the LUMO polarised towards the R group. This assignment from TD-DFT is591

consistent with experimental resonance Raman results which show enhance-592

ment of triazole and nitrophenyl bands where R−−NO2Ph and pyridine bands593

for all other substituents.594

Substitution is shown to have some effect on emission spectra, which595

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range from λem,max of 538 nm when R−−Ph and Bn to 520 nm for the steroid,596

no emission was observed for the nitrophenyl containing complex. Emission597

lifetimes are much shorter than in the ‘regular’-type triazoles and little dis-598

tinction is made between different substituents with τ between 13 and 17 ns.599

Additionally emission efficiencies are much smaller at ∼ 0.00015 except for600

R−−Ph (0.00043) and R−−steroid (0.00083). This is consistent with the idea601

that adding the methylene bridge increases the flexibility of the ligand and602

leads to non radiative decay through new pathways[72]. Electrochemistry603

gave similar results to the ‘regular’-type triazoles except that the ReI/ReII604

oxidation is now quasi-reversible. This is likely due to the extra stabilisation605

afforded by the (now) 6-membered chelate ring.606

A rhenium tridentate ‘inverse’-type complex (Figure 16) has also been607

reported [63] with aromatic (R−−Ph) or alkyl (R−−C3H7) substituents. The608

absorption spectrum includes the two transitions seen for the bidentate609

‘inverse’ analogue with R−−Ph (however the higher energy transition is610

now predicted to be ILCT in nature, πtriazole→ π*pyridine) as well as an611

additional ILCT band at 264 nm (predicted from TD-DFT). The excited612

properties show a number of differences in comparison to the bidentate613

inverse analogue Re(CO)3Cl(pyCH2triaCH2Ph). The emission bands (λem)614

red-shift, the excited state lifetimes (τ) and quantum yields (φ) increase.615

For Re(CO)3Cl(py(CH2triaPh)2) λem = 613 nm (in comparison to 537 nm616

for Re(CO)3Cl(pyCH2triaCH2Ph)) with τ = 62 ns and φ = 0.0014. For617

Re(CO)3Cl(py(CH2triaC3H7)2) these values are 605 nm, 87 ns and 0.0012618

respectively.619

‘Regular’-type tridentate homoleptic ruthenium complexes (R−−Bn and620

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Figure 16: Rhenium tridentate ‘inverse’-type complex studied in reference [63]

polystyrene), analogous to the bidentate complexes described in the preced-621

ing section, show a slight red-shift in the absorption spectrum from 383 nm622

(for the bidentate analogue) to 394 nm (for the tridentate).[56]623

Heteroleptic tridentate ‘regular’ type ruthenium complexes have been in-624

vestigated where terpyridine (tpy) acts as the ancillary ligand.[64]625

Ru(tpy)(py(tria-R)2)Ru(tpy)2Ru(py(tria-R)2)2

Figure 17: Electronic absorption spectrum of the heteroleptic tridentate ‘regular’ type

ruthenium complexes (R = C10H21) compared to its homoleptic counterparts. Figure

adapted from ref [64].

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The MLCT band observed, Figure 17, for the heteroleptic complex (342626

nm) is intermediary between the two homoleptic complexes, that is, where627

both ligands are either py(triaC10H21)2 (394 nm) or tpy (474 nm). The blue628

shift compared to the homoleptic compound is attributed to better back-629

bonding with the triazole ligand, lifting the LUMO (π*ligand) and lowering630

the HOMO (metal d orbitals). The ligand centered transition at around 290631

nm is also split into two bands due to two different LC transitions. The632

authors conclude that substitution on the triazole has little effect on the633

electronic properties. The same blue-shift is seen in the emission spectrum634

(at 77 K) when a ligand in the tpy homoleptic complex is exchanged for a635

py(triaR)2 ligand, by around 20 nm. The authors note that no emission is636

observed from the homoleptic triazole ligand complex due to the stronger637

π-accepting ability of the triazole ligands increasing the 3MLCT state up638

towards the 3MC state which is coupled strongly to the ground state. Cyclic639

voltammetry showed that the HOMO is relatively unchanged by the number640

of triazole containing ligands while the LUMO is strongly destabilized from641

-1.23 to -1.36 to -1.70 V with increasing py(triaR)2 ligands.642

Iridium complexes are also able to form bidentate complexes with the643

‘regular’-type pytriaR ligand chelating through the pyridine nitrogen and644

the triazole carbon. A series of heteroleptic complexes with ppy ancillary645

ligands[58] and various R groups show electronic absorption spectra with646

the same profile as seen for coordination through the triazole nitrogen. No647

difference is observed with different substitution at R and the transitions648

are assigned as above. The observation of hypsochromic shift when F2ppy649

replace ppy (Figure 14, where R2=H) supports the view that the electronics650

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are based on this ligand rather than pytriaR.651

Emission band profiles are much less structured than when chelated652

through the triazole nitrogen, their position is also insensitive to R but653

their intensity is affected. This finding is attributed to aggregation–induced654

quenching processes being minimized with some R groups and not others.655

For example, where R−−(CH2)2C8F17 the quantum yield is three times greater656

(0.007) than when R−−(CH2)5CH3 (0.002). The lifetime is also affected by657

the nature of R ranging from 0.2 to 2 µs.658

TD-DFT was employed to determine the nature of the HOMO and the659

LUMO. The LUMO is sensitive to triazole coordination through N rather660

than C. In this case the LUMO is localized on the ppy ligand specifically that661

has a transoid Ir-C bond with the pytria ligand. Now the low lying absorption662

is assigned as a 3MLCT and 3LC (based on the ppy ligand) transition. This663

can explain the less structured nature of the emission spectrum. The pytria664

ligand is a more capable π acceptor when coordinated through N rather than665

C, leading to increased back-bonding and splitting of the HOMO and LUMO666

through appropriate orbital stabilization and destabilization. It also explains667

the shift in the emission spectra.668

3.2. Other Triazole Heterocycles669

Phenyl-triazole (triaPh) ligands have also been investigated as both670

mono- and bi-dentate ligands (Figure 18).671

A series of monodentate RtriaPhR rhenium tricarbonyl bpy complexes,672

shown in Figure 19[65], show that substitution at either the triazole or phenyl673

does not affect the absorption spectrum with bands unshifted from ‘regular’-674

type pytriaR spectrum. Interestingly however the MLCT band observed at675

44

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iptN N

NR

NN N N N

NR R

N

N

N

N

NN

RR

ϕ-(triaR)2RtriaPh bitriaR

Figure 18: Different triazole containing ligand types.

338 nm is now described by TD-DFT as terminating on the bpy ligand.676

For some of the substituents the emission maxima occur slightly red-shifted677

compared to the pytriaR complexes (532 nm), at between 552 and 543 nm.678

However the emission maximum of Re(bpy)(CO)3(PhCH2triaPh) is virtually679

unshifted with respect to complexes with ‘regular’-type pytriaR at 535 nm.680

Lifetimes, in MeCN, are also comparable to the pytriaR complexes (τ up to681

160 ns) at between 130-140 ns. When measured in DCM, they are consider-682

ably longer, at 475 to 513 ns, consistent with a 3MLCT emissive state.683

N

NRe

CO

CO

CO

NN

N

R1

R2

+ R1

CH3

C3H7

PhCH2

C3H7

R2

HHHCH3

Ligand code

MetriaPhPrtriaPhPhCH2triaPhPrtriaPhMe

Figure 19: Monodentate [Re(CO)3(bpy)(RtriaPhR)]+

complexes investigated by Uppal et

al.[65]

The use of φ(triaR)2 as a tridentate ligand for ruthenium in heterolep-684

tic complexes with tpy shows an electronic absorption spectrum that in-685

cludes bands observed in the Rpytria heteroleptic Ru complexes at around686

370 nm[66]. For [Ru(tpy)φ(trianBu)2]2+ this band lies at 367 nm, shifting687

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to 378 nm in [Ru(tpy)φ(triaPh)2]2+. This band is assigned as an MLCT688

transition terminating on the φ(triaR)2 ligand based on previous studies[73]689

on various phenyl-pyridine tridentate ligands. Cyclic voltammetry behaviour690

was similar for both the triazole and phenyl substitution: two oxidations on691

the Ru were observed ca. +0.55 and 1.62 V while reductions were seen at692

ca. -1.55 (tpy) and -1.94 V (the phenyl-triazole ligand).693

Table 6: Electrochemical data for triazole compounds. Compounds discussed in detail in

text are shown in bold.

Compound Eox /V Ered /V Solvent Std electrode Reference

Re(CO)3Cl(pytriaC8H17) -1.74 DCM DMFc/DMFc+ [52]

Re(CO)3Cl(pytriaCH2Ph) -1.72 DCM DMFc/DMFc+ [52, 53]

Re(CO)3Cl(pytriaCH2PhOMe) -1.72 DCM DMFc/DMFc+ [52]

Re(CO)3Cl(pytriaCH2PhNO2) -1.53, -0.94 DCM DMFc/DMFc+ [52]

Re(CO)3Cl(pytriaPh) DCM DMFc/DMFc+ [52]

Re(CO)3Cl(pytriaFc) 0.85 -1.71 DCM DMFc/DMFc+ [52]

Re(CO)3Cl(pytriaPhOMe) -1.68 DCM DMFc/DMFc+ [52]

Re(CO)3Cl(pytriaPhNO2) -1.73, -1.31, -0.81 DCM DMFc/DMFc+ [52]

[Ir(F2ppy)2(pytria−ada)]+ 1.22 -2.18, -2.59 Fc/Fc+ [57]

[Ir(F2ppy)2(pytriaCH2Ph)]+ 1.27 -2.17, -2.59 Fc/Fc+ [57]

[Ir(F2ppy)2(pytriaPh)]+ 1.19 -2.02, -2.44 Fc/Fc+ [57]

[Ir(F2ppy)2(pytriabiPh)]+ 1.26 -2.08, -2.52 Fc/Fc+ [57]

[Ru(bpy)2(pytriaC10H21)]2+ 1.16 -1.55 DCM Ag/Ag+ [55]

[Ru(bpy)(pytriaC10H21)2]2+ 1.2 -1.64 DCM Ag/Ag+ [55]

[Ru(pytriaC10H21)3]2+ 1.26 DCM Ag/Ag+ [55]

[Ru(bpy)2(pytriaC11H22OH)]2+ 1.46 DCM Ag/Ag+ [55]

[Ru(pytria−nap)3]2+ 1.2 -1.5 DCM Ag/Ag+ [55]

[Ru(bpy)2(pytria−nap)]2+ 1.24 -1.48 DCM Ag/Ag+ [55]

[Ru(bpy)2(pytriaPhOMe)]2+ 1.23 -1.49 DCM Ag/Ag+ [55]

[Ru(dmbpy)2(H2)]2+ 0.88 -1.34, -1.97, -2.18 MeCN Fc/Fc+ [59, 60]

[Ru(dmbpy)2(H3)]2+ 0.84 -1.89, -2.13 MeCN Fc/Fc+ [60]

[Ru(dmbpy)2(H4)]2+ 0.88 -1.36, -1.98, -2.11 MeCN Fc/Fc+ [60]

[Ru(dmbpy)2(H5)]2+ 0.84 -1.85, -2.03, -2.18 MeCN Fc/Fc+ [60]

[Ru(dmbpy)2(H1)]2+ 0.82, 1.28 -1.85, -2.06, -2.23 MeCN Fc/Fc+ [59, 60]

Re(CO)3Cl(pyCH2triaPh) 1.5 -1.75 DCM DMFc/DMFc+ [62]

Re(CO)3Cl(py−CH2triaPhNO2) 1.54 -1.63, -0.94 DCM DMFc/DMFc+ [62]

Re(CO)3Cl(pyCH2tria−PhOMe) 1.49 -1.74 DCM DMFc/DMFc+ [62]

Re(CO)3Cl(pyCH2tria−PhCH2Ph) 1.5 -1.77 DCM DMFc/DMFc+ [62]

Re(CO)3Cl(pyCH2tria−caf) 1.54 -1.7 DCM DMFc/DMFc+ [62]

Re(CO)3Cl(pyCH2tria−ster) 1.54 -1.75 DCM DMFc/DMFc+ [62]

[Ru(tpy)(py(triaC10H21)2)]2+ 1.34 -1.36 DCM SHE [64]

[Ru(tpyPhBr)(py(triaC10H21)2)]2+ 1.33 -1.3 DCM SHE [64]

[Ru(tpyPhBr)(py(triaPhOMe)2)]2+ 1.35 -1.3 DCM SHE [64]

[Ru(tpyPhBr)(py(triaCH2PhBu)2)]2+ 1.35 -1.28 DCM SHE [64]

[Ru(tpy)2]2+ 1.33 -1.23 DCM SHE [64]

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[Ru(py(triaC10H21)2)2]2+ 1.34 -1.7 DCM SHE [64]

[Ru(tpy)φ(trianBu)2]2+ 0.53, 1.60 -1.57, -1.95 MeCN Ag/Ag+ [66]

[Ru(tpy)φ(triaPh)2]2+ 0.58, 1.64 -1.53, -1.89 MeCN Ag/Ag+ [66]

[Ru(tpy)φ(triaBr)2]2+ 0.56, 1.66 -1.35, -1.58, -1.96 MeCN Ag/Ag+ [66]

[Ru(bitriaC6H13)3]2+ 1.35 -2.30 MeCN Ag/Ag+ [68]

[Ru(bitriaC6H13)3]2+ 1.49 -2.30 MeCN Ag/Ag+ [68]

[Cu(diphos)(L1)] 0.37 THF Fc/Fc+ [69]






[Ru(bpy)2(pytriaPh(OMe)2)]+ 0.80, 1.20, 1.40 -1.48, -1.76 MeCN SCE [70]

[Ru2(bpy)4(pytria2Ph(OMe)2)]2+ 0.82, 1.26, 1.45 -1.48, -1.73 MeCN SCE [70]

[Ru(bpy)2(pytria)]+ 0.83 -1.47, -1.72, -2.25 MeCN SCE [70]

[Ru2(bpy)4(pytriapy)]3+ 1.04, 1.34 -1.40, -1.62, -1.67 MeCN SCE [70]

A number of heteroleptic iridium complexes have been reported[67] where694

one pytriaR ligand and two phtriaMe ligands are coordinated to the metal.695

Again the authors report a lack of communication through the triazole rings696

when comparing the absorption spectra for various R groups: Me, ada, βCD.697

1(π, π*) bands are seen in the UV region (as they are in the pytriaR complex698

with ppy ancillary ligands) at 190-250 nm based on both ligands. The weaker,699

lower energy CT transitions, both 1MLCT and 3MLCT, are observed to blue-700

shift by around 50 nm to 300 - 350 nm. The room temperature (RT) emission701

spectra are quite broad and featureless, in contrast to [Re(pytria)(ppy)2]702

complexes, with a maximum at 510 nm. This is characteristic of a purely703

MLCT transition rather than a mixture of MLCT and LC transitions. Both704

lifetimes and emission efficiencies, under argon, are smaller than their ppy705

containing analogues. Quantum yields are between 0.05-0.1 except where706

R=βCD (0.25) compared to 0.15-0.24, while lifetimes are 20 - 30 ns compared707

to around 750 ns. The efficiency of the βCD containing complex may be708

explained by its affinity to aggregate and the subsequent reduction of non-709

radiative decay through vibrational modes.710

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Another type of triazole-containing ligand is the bitriazole (bitriaR)711

shown in Figure 18. These have been reported by Fletcher et al.[68] as712

homoleptic ruthenium complexes with R = n-C6H13 and Ph. Both the713

π, π* and the MLCT band are blue-shifted significantly compared to the714

homoleptic pytriaR complex, from 384 nm to around 310 nm. Fluorescence715

was not observed for either complex at room temperature. The authors716

report a shift to more negative potentials for the ligand centered reduction717

in cyclic voltammetry with increasing numbers of triazoles coordinated to718

the ruthenium. This is consistent with a higher π* energy level because of719

the electron rich triazole rings relative to pyridine. The RuII/RuIII oxidation720

potentials are shifted about 70 mV when the alkyl unit is replaced with an721

aryl one, from 1.4 to 1.5 V.722

Another different system is based on amido-triazolato ligand bound to723

copper (Figure 20)[69] .724

NN

NR2

NCu

R3R3

R1

P

Ph2

P

Ph2

L1 R1=H, R2=Ph, R3=H

L2 R1=CH3, R2=Ph, R3=H

L3 R1=OCH3, R2=Ph, R3=H

L4 R1=Cl, R2=Ph, R3=H

L5 R1=H, R2=Ph, R3=CH3

L6 R1=H, R2=Bn, R3=CH3

Figure 20: Copper complex with an amido-triazolato type ligand, [Cu(diphos)(L)]

The electronic absorption spectra are similar with three main bands, a725

π, π* band near 300 nm, a shoulder at around 350 nm and a band at around726

420 nm. This lower energy band is blue-shifted modestly (by 10-20 nm) from727

the methoxy-substituted complex to the chloro-substituted complex. The728

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trend is consistent with increasing the HOMO energy with greater electron729

density from the para-substituent to the amide donor. The shoulder near 350730

nm is red-shifted for the same substituent indicating that here the LUMO is731

affected, perhaps indicating an ILCT transition, versus an MLCT transition732

for the low energy band.733

The emission spectra were relatively unaffected by different substitution734

with maxima at 631-633 nm and a shoulder at 650-667 nm. Lifetimes range735

considerably from several hundred ns to around 3 µs and are affected con-736

siderably by the solvent, those in benzene are 2-3 times longer than in THF.737

The same is seen for the quantum yields, ranging from 0.0004-0.026, this738

suggests a triplet emissive state.739

TD-DFT calculations were performed to ascertain the nature of the elec-740

tronic transitions. These showed that the HOMO was invariably based on741

the metal d orbitals and the aryl amido ligand π orbital, [Cu(diphos)(L3)] has742

the highest energy HOMO and is the easiest to oxidize (Table 6) in the series,743

whereas [Cu(diphos)(L4)] has the lowest calculated HOMO and is the most744

difficult complex to oxidize. The LUMO however is dependent on the nature745

of the triazole, that is, where the N1 substituent (R) is phenyl the LUMO is746

based on the triazole and the emissive state is described as 3(MLCT+ILCT).747

If the N1 substituent is Bn on the other hand the LUMO is now phosphine748

based and the excited state is thus 3(MLCT+LLCT).749

3.3. Bridging triazole ligands750

Triazole ligands can also be used to bridge metal atoms[70] using751

1,2,4-pytria ligands (Figure 21). The electronic absorption and emis-752

sion spectra show shifts with substituents on the triazole ligand. For753

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N N N

N

Ru(bpy)2

N N N

N

Ru(bpy)2

OMe

OMe

N

NN N

(bpy)2Ru

NRu(bpy)2

N N N

N

Ru(bpy)2

N N N

N

Ru(bpy)2

OMe

OMe

MLCT(abs) = 485 nm 481 nm 465 nm 453 nmMLCT(em) = 685 nm 683 nm 650 nm 648 nm

[Ru(bpy)2(pytriaPh(OMe)2)]+ [Ru2(bpy)4(pytria2Ph(OMe)2)]

2+ [Ru(bpy)2(pytria)]+ [Ru2(bpy)4(pytriapy)]3+

+ 2+

+

3+

Figure 21: Pyridine triazole bridging type ligand complexes with ruthenium

[Ru(bpy)2(pytria)]+ the lowest energy transition at 465 nm is shifted to754

485 nm in [Ru(bpy)2(pytriaPh(OMe)2)]+. These ligands may be extended755

to make bridging ligands and the corresponding binuclear complexes show756

similar shifts with subtitution (Table 5). The emission spectra are also757

affected more by the functionalisation of C3 of the triazole than the second758

metallation. Lifetimes (at RT in MeCN) are all around 105 ns with the759

exception of the unfunctionalised singly metallated complex where τ = 145760

ns. Cyclic voltammetry (vs SCE) showed that the RuII/RuIII oxidation oc-761

curs at around 0.82 V except for the double metallated unfunctionalised one762

which has two at 1.04 V and 1.34 V. Ligand based reductions are also very763

similar (-1.48, -1.74 V) except for the same species (-1.40, -1.62, -1.67 V).764

The authors also report that interaction between the metal centres is weak765

in the dinuclear complexes but does exist. This interaction is considerably766

lessened in the species with a dimethoxyphenyl spacer, consistent with the767

increased separation of the metal centres.768

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4. Conclusions769

The changes in properties for dppz ligands and their complexes have been770

studied systematically. From these data, tuning of either the phz or phen771

MO may be accomplished and these modifications are evident in electro-772

chemical and spectroscopic studies. The electronic properties of substituted773

dppz systems are dominated by ligand-centered and MLCT transitions. It is774

notable that the π*(phen) and π*(phz) MOs may be independently tuned;775

the MO partitioning remains relatively uncompromised by substituent ef-776

fects. With the use of strong donor substituents it is also possible to obtain777

ILCT transitions.778

In the case of triazole systems the effect of substituents is less evident.779

What is clear is that conjugation at the triazole has some effect; whereas780

if the substituent unit is saturated no effect is observed. It appears that781

tuning N1 of the 1,2,3-triazole has very little effect on the ground state prop-782

erties but a reasonable effect on the excited state properties. Additionally,783

tuning other heterocycles involved in coordination has a significant effect on784

both properties, for example substituting electron donating / withdrawing785

substituents at the para- position of the pyridine in Rpytria type complexes.786

Triazole systems offer the possibility of programming properties, such as sol-787

ubility, into a complex without perturbation of the photophysical or optical788

behaviour.789

5. Acknowledgements790

Support from the University of Otago, Royal Society of New Zealand and791

MacDiarmid Institute is gratefully acknowledged.792

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6. References793

[1] A. A. Schilt, Analytical applications of 1,10-phenanthroline and related794

compounds, Pergammon Press, Oxford, UK, 1969.795

[2] M. Eggleston, D. McMillin, K. Koenig, A. Pallenberg, Inorg. Chem. 36796

(1997) 172–176.797

[3] A. Juris, S. Campagna, I. Bidd, J. Lehn, R. Ziessel, Inorg. Chem. 27798

(1988) 4007–4011.799

[4] A. Lever, Inorg. Chem. 30 (1991) 1980–1985.800

[5] V. Balzani, A. Juris, M. Venturi, S. Campagna, S. Serroni, Chem. Rev.801

96 (1996) 759–833.802

[6] R. Horvath, K. C. Gordon, Inorg. Chim. Acta 374 (2011) 10–18.803

[7] A. E. Friedman, J.-C. Chambron, J.-P. Sauvage, N. J. Turro, J. K.804

Barton, J. Am. Chem. Soc. 112 (1990) 4960–4962.805

[8] M. K. Brennaman, T. J. Meyer, J. M. Papanikolas, J. Phys. Chem. A806

108 (2004) 9938–9944.807

[9] M. R. Waterland, K. C. Gordon, J. J. McGarvey, P. M. Jayaweera,808

Dalton Trans. (1998) 609–616.809

[10] A. Arancibia, J. Concepcion, N. Daire, G. Leiva, A. M. Leiva, B. Loeb,810

R. D. Ro, R. Daz, A. Francois, M. Saldivia, J. Coord. Chem. 54 (2001)811

323–336.812

52

of 60

Accep

ted

Man

uscr

ipt

[11] J. Fees, W. Kaim, M. Moscherosch, W. Matheis, J. Klima, M. Krejcik,813

S. Zalis, Inorg. Chem. 32 (1993) 166–174.814

[12] M. R. Waterland, K. C. Gordon, J. Raman Spectrosc. 31 (2000) 243–253.815

[13] K. Butsch, R. Gust, A. Klein, I. Ott, M. Romanski, Dalton Trans. 39816

(2010) 4331–4340.817

[14] M. G. Fraser, A. G. Blackman, G. I. S. Irwin, C. P. Easton, K. C.818

Gordon, Inorg. Chem. 49 (2010) 5180–5189.819

[15] J. D. Aguirre, H. T. Chifotides, A. M. Angeles-Boza, A. Chouai,820

C. Turro, K. R. Dunbar, Inorg. Chem. 48 (2009) 4435–4444.821

[16] N. J. Lundin, P. J. Walsh, S. L. Howell, J. J. McGarvey, A. G. Blackman,822

K. C. Gordon, Inorg. Chem. 44 (2005) 3551–3560.823

[17] M. K. Kuimova, W. Z. Alsindi, A. J. Blake, E. S. Davies, D. J. Lam-824

pus, P. Matousek, J. McMaster, A. W. Parker, M. Towrie, X.-Z. Sun,825

C. Wilson, M. W. George, Inorg. Chem. 47 (2008) 9857–9869.826

[18] A. Kleineweischede, J. Mattay, J. Organomet. Chem. 691 (2006) 1834–827

1844.828

[19] L. Sanhueza, M. Barrera, I. Crivelli, Polyhedron 57 (2013) 94–104.829

[20] J. Rusanova, S. Decurtins, E. Rusanov, H. Stoeckli-Evans, S. Delahaye,830

A. Hauser, Dalton Trans. (2002) 4318–4320.831

[21] N. J. Lundin, P. J. Walsh, S. L. Howell, A. G. Blackman, K. C. Gordon,832

Chem. Eur. J. 14 (2008) 11573–11583.833

53

of 60

Accep

ted

Man

uscr

ipt

[22] G. David, P. J. Walsh, K. C. Gordon, Chem. Phys. Lett. 383 (2004)834

292–296.835

[23] B. Schafer, H. Gorls, M. Presselt, M. Schmitt, J. Popp, W. Henry, J. G.836

Vos, S. Rau, Dalton Trans. (2006) 2225–2231.837

[24] P. J. Walsh, N. J. Lundin, K. C. Gordon, J.-Y. Kim, C.-H. Lee, Opt.838

Mater. 31 (2009) 1525–1531.839

[25] C.-S. Choi, T. Mutai, S. Arita, K. Araki, J. Chem. Soc. Perk. T. 2 (2000)840

243–247.841

[26] R. M. Hartshorn, J. K. Barton, J. Am. Chem. Soc. 114 (1992) 5919–842

5925.843

[27] E. Amouyal, A. Homsi, J.-C. Chambron, J.-P. Sauvage, Dalton Trans.844

(1990) 1841–1845.845

[28] Y.-H. Zhou, Z.-M. Wang, M.-D. Chen, S.-L. Guo, Y.-X. Zheng, J. Coord.846

Chem. 66 (2013) 958–965.847

[29] W. Chen, C. Turro, L. A. Friedman, J. K. Barton, N. J. Turro, J.848

Phys.Chem. B 101 (1997) 6995–7000.849

[30] J. Dyer, C. M. Creely, J. C. Penedo, D. C. Grills, S. Hudson, P. Ma-850

tousek, A. W. Parker, M. Towrie, J. M. Kelly, M. W. George, Pho-851

tochem. Photobio. Sci. 6 (2007) 741–748.852

[31] M. K. Kuimova, D. C. Grills, P. Matousek, A. W. Parker, X.-Z. Sun,853

M. Towrie, M. W. George, Vib. Spectrosc. 35 (2004) 219–223.854

54

of 60

Accep

ted

Man

uscr

ipt

[32] C. Kuhnt, S. Tschierlei, M. Karnahl, S. Rau, B. Dietzek, M. Schmitt,855

J. Popp, J. Raman Spectrosc. 41 (2010) 922–932.856

[33] C. Kuhnt, M. Karnahl, S. Tschierlei, K. Griebenow, M. Schmitt,857

B. Schafer, S. Krieck, H. Gorls, S. Rau, B. Dietzek, J. Popp, Phys.858

Chem. Chem. Phys. 12 (2010) 1357–1368.859

[34] M. Yamada, Y. Tanaka, Y. Yoshimoto, S. Kuroda, I. Shimao, Bull.860

Chem. Soc. Jpn. 65 (1992) 1006–1011.861

[35] N. Komatsuzaki, R. Katoh, Y. Himeda, H. Sugihara, H. Arakawa, K. Ka-862

suga, Dalton Trans. (2000) 3053–3054.863

[36] C. Goze, C. Leiggener, S.-X. Liu, L. Sanguinet, E. Levillain, A. Hauser,864

S. Decurtins, ChemPhysChem 8 (2007) 1504–1512.865

[37] C. Jia, S.-X. Liu, C. Tanner, C. Leiggener, A. Neels, L. Sanguinet,866

E. Levillain, S. Leutwyler, A. Hauser, S. Decurtins, Chem. Eur. J. 13867

(2007) 3804–3812.868

[38] N. Dupont, Y.-F. Ran, S.-X. Liu, J. Grilj, E. Vauthey, S. Decurtins,869

A. Hauser, Inorg. Chem. 52 (2013) 306–312.870

[39] M. Yanez, J. Guerrero, P. Aguirre, S. A. Moya, G. Cardenas-Jiron, J.871

Organomet. Chem. 694 (2009) 3781–3792.872

[40] C.-S. Choi, L. Mishra, T. Mutai, K. Araki, Bull. Chem. Soc. Jpn. 73873

(2000) 2051–2058.874

[41] R. Bolligarla, S. K. Das, Tetrahedron Lett. 52 (2011) 2496–2500.875

55

of 60

Accep

ted

Man

uscr

ipt

[42] L. Tan, J. Shen, J. Liu, L. Zeng, L. Jin, C. Weng, Dalton Trans. 41876

(2012) 4575–4587.877

[43] Y. Sun, D. A. Lutterman, C. Turro, Inorg. Chem. 47 (2008) 6427–6434.878

[44] M. G. Fraser, H. van der Salm, S. A. Cameron, J. E. Barnsley, K. C.879

Gordon, Polyhedron 52 (2013) 623–633.880

[45] J. E. Hein, V. V. Fokin, Chem. Soc. Rev. 39 (2010) 1302–1315.881

[46] A. M. Pizarro, P. J. Sadler, Biochimie 91 (2009) 1198–1211.882

[47] I. Bratsos, D. Urankar, E. Zangrando, P. Genova-Kalou, J. Komrlj,883

E. Alessio, I. Turel, Dalton Trans. 40 (2011) 5188–5199.884

[48] C. Ulbricht, B. Beyer, C. Friebe, A. Winter, U. S. Schubert, Adv. Mater.885

21 (2009) 4418–4441.886

[49] A. Tsuboyama, H. Iwawaki, M. Furugori, T. Mukaide, J. Kamatani,887

S. Igawa, T. Moriyama, S. Miura, T. Takiguchi, S. Okada, M. Hoshino,888

K. Ueno, J. Am. Chem. Soc. 125 (2003) 12971–12979.889

[50] S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq, R. Kwong,890

I. Tsyba, M. Bortz, B. Mui, R. Bau, M. E. Thompson, Inorg. Chem. 40891

(2001) 1704–1711.892

[51] A. B. Tamayo, B. D. Alleyne, P. I. Djurovich, S. Lamansky, I. Tsyba,893

N. N. Ho, R. Bau, M. E. Thompson, J. Am. Chem. Soc. 125 (2003)894

7377–7387.895

56

of 60

Accep

ted

Man

uscr

ipt

[52] T. Y. Kim, A. Elliott, K. J. Shaffer, C. John McAdam, K. C. Gordon,896

J. D. Crowley, Polyhedron 52 (2013) 1391–1398.897

[53] M. Obata, A. Kitamura, A. Mori, C. Kameyama, J. A. Czaplewska,898

R. Tanaka, I. Kinoshita, T. Kusumoto, H. Hashimoto, M. Harada, Dal-899

ton Trans. (2008) 3292–3300.900

[54] M. Felici, P. Contreras-Carballada, Y. Vida, J. M. Smits, R. J. Nolte,901

L. De Cola, R. M. Williams, M. C. Feiters, Chem. Eur. J. 15 (2009)902

13124–13134.903

[55] B. Happ, C. Friebe, A. Winter, M. Hager, R. Hoogenboom, U. Schubert,904

Chem. Asian J. 4 (2009) 154–163.905

[56] C. Zhang, X. Shen, R. Sakai, M. Gottschaldt, U. S. Schubert, S. Hiro-906

hara, M. Tanihara, S. Yano, M. Obata, N. Xiao, T. Satoh, T. Kakuchi,907

J. Polym. Sci. A Polym. Chem. 49 (2011) 746–753.908

[57] M. Mydlak, C. Bizzarri, D. Hartmann, W. Sarfert, G. Schmid,909

L. De Cola, Adv. Funct. Mater. 20 (2010) 1812–1820.910

[58] S. Liu, P. Muller, M. K. Takase, T. M. Swager, Inorg. Chem. 50 (2011)911

7598–7609.912

[59] D. Escudero, B. Happ, A. Winter, M. D. Hager, U. S. Schubert, L. Gon-913

zlez, Chem. Asian J. 7 (2012) 667–671.914

[60] B. Happ, D. Escudero, M. D. Hager, C. Friebe, A. Winter, H. Grls,915

E. Altunta, L. Gonzlez, U. S. Schubert, J. Org. Chem. 75 (2010) 4025–916

4038.917

57

of 60

Accep

ted

Man

uscr

ipt

[61] H. J. Park, J. N. Kim, H.-J. Yoo, K.-R. Wee, S. O. Kang, D. W. Cho,918

U. C. Yoon, J. Org. Chem. 78 (2013) 8054–8064.919

[62] C. B. Anderson, A. B. S. Elliott, C. J. McAdam, K. C. Gordon, J. D.920

Crowley, Organometallics 32 (2013) 788–797.921

[63] C. B. Anderson, A. B. S. Elliott, J. E. M. Lewis, C. J. McAdam, K. C.922

Gordon, J. D. Crowley, Dalton Trans. 41 (2012) 14625–14632.923

[64] B. Schulze, C. Friebe, M. D. Hager, A. Winter, R. Hoogenboom,924

H. Gorls, U. S. Schubert, Dalton Trans. (2009) 787–794.925

[65] B. S. Uppal, R. K. Booth, N. Ali, C. Lockwood, C. R. Rice, P. I. P.926

Elliott, Dalton Trans. 40 (2011) 7610–7616.927

[66] W.-W. Yang, L. Wang, Y.-W. Zhong, J. Yao, Organometallics 30 (2011)928

2236–2240.929

[67] M. Felici, P. Contreras-Carballada, J. M. Smits, R. J. Nolte, R. M.930

Williams, L. De Cola, M. C. Feiters, Molecules 15 (2010) 2039–2059.931

[68] J. T. Fletcher, B. J. Bumgarner, N. D. Engels, D. A. Skoglund,932

Organometallics 27 (2008) 5430–5433.933

[69] G. F. Manbeck, W. W. Brennessel, R. Eisenberg, Inorg. Chem. 50 (2011)934

3431–3441.935

[70] P. Passaniti, W. R. Browne, F. C. Lynch, D. Hughes, M. Nieuwen-936

huyzen, P. James, M. Maestri, J. G. Vos, J. Chem. Soc., Dalton Trans.937

(2002) 1740–1746.938

58

of 60

Accep

ted

Man

uscr

ipt

[71] W. R. Browne, W. Henry, P. Passaniti, M. T. Gandolfi, R. Ballardini,939

C. M. O’Connor, C. Brady, C. G. Coates, J. G. Vos, J. J. McGarvey,940

Photochem. Photobio. Sci. 6 (2007) 386–396.941

[72] J. Herbich, W. Rettig, R. Thummel, J. Waluk, Chem. Phys. Lett. 195942

(1992) 556–562.943

[73] S. H. Wadman, M. Lutz, D. M. Tooke, A. L. Spek, F. Hartl, R. W. A.944

Havenith, G. P. M. van Klink, G. van Koten, Inorg. Chem. 48 (2009)945

1887–1900.946

59

of 60

Accep

ted

Man

uscr

ipt

Highlights file

We review substituent effects in complexes with dppz and triazole ligands

Modulation of dppz properties is associated with the phenazine or phenanthroline MOs

Dppz with donor groups give ligand-centered charge-transfer optical transitions

For triazoles optical properties do not alter with substituent

Excited state properties of triazole complexes give a muted response to substituent

*Highlights (for review)

substituent effects on the electronic properties of complexes with dipyridophenazine and triazole...

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