1  

Supporting Information for

Photochemical  Upconversion  in  Water      Karim  A.  El  Roza  and  Felix  N.  Castellano*a    

aDepartment  of  Chemistry,  North  Carolina  State  University,  Raleigh,  NC  27695-­‐8204,  USA      Corresponding Author *Email: fncastel@ncsu.edu      

Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2017

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Experimental Section General: [Ru(bpy)3]Cl2 was purchased from Sigma Aldrich and used without further purification. Na4[Ru(BPS)3] was synthesized and purified as previously reported in the literature.1,2 9-Anthracenecarboxylic acid (AnCO2H) and 1-Pyrenecarboxylic acid (PyCO2H) were purchased from Sigma Aldrich. Each carboxylic acid compound was treated with hot sodium hydroxide in water, under vigorous stirring overnight, followed by recrystallization from acetone to yield the sodium salts 9-Anthracenecarboxylate anion (AnCO2

-) and 1-Pyrenecarboxyalte anion (PyCO2-) respectively.3 Unlike the conjugate

acid form, the aromatic hydrocarbon salts, Na[AnCO2] and Na[PyCO2], are water-soluble. Spectroscopic samples were placed in a 1 cm path length Starna cell (quartz) cuvette, bubble-degassed with argon gas for at least 40 min where they remained under positive inert atmosphere during the course of the photospectroscopic experiments. HPLC grade water (H2O) was purchased from J.T. Baker. Absorption spectra were measured using Cary 50 or Agilent 845 diode array spectrophotometer. Static emission spectra were collected from FL/FL920 spectrofluorometer (Edinburgh Instruments) and corrected for emission detector response. Stern-Volmer Kinetics: Using steady state dynamic quenching, the Stern-Volmer constant (ksv) and the bimolecular quenching rate (kq) were extrapolated from photoluminescence lifetime experiments according to the Stern-Volmer relation, τ0/τ = 1+Ksv[Q] where τ0 and τ are the sensitizer lifetimes of the unquenched and quenched emission respectively and KSV = kqτ0. The slope (Ksv) was linear upon the addition of [Q], molar concentration of quencher/acceptor. The samples were excited using a Nitrogen-pumped dye laser at 442 nm to selectively excite the Ru(II) MLCT band in the absorption spectra. The absorbance of the sensitizers was chosen to be optically-dilute at the excitation wavelength (0.1 - 0.2). All samples were bubbled degassed for 40 min before the start of the experiment. Transient Optical Spectroscopy: The optical density of the samples at 452 nm excitation wavelength was ∼ 0.35. The laser pulse excitation source was from a Vibrant 355 LD-UVM Nd:YAG/OPO system (OPOTEK) (∼3 mJ/pulse, 5 ns fwhm). The transient absorption data collected was from an LP920 laser flash photolysis (Edinburgh Instruments) with an iStar ICCD Camera (Andor), and the kinetic traces were acquired using a PMT (R928 Hamamatsu). Exponential decays were fitted accordingly using Origin 9.1. Upconversion Power Dependence Experiment: The upconverted photoluminescence detected from FL/FLS 920 spectrofluorometer was a result of a continuous laser-beam excitation from an Argon/Krypton ion laser (Innova 70C Coherent) excited at 488 nm or 514.5 nm (∼ 1 mm diameter spot). A Nova II/PD300-UV power meter was used to determine the excitation power before reaching the sample. The appropriate filters were positioned in front of the incident laser to filter-out all wavelengths except the excitation wavelength issued from the laser preventing direct absorption of the acceptor. No emission was observed when samples were irradiated at 488 nm in the absence of sensitizer. For the power dependence experiment, neutral density filters were used to

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adjust the laser power prior to exciting the sample. To gain an improved upconverted emission profile, a spatial geometry adjustment of sample illumination was used to correct for the inner-filter effect.4–6 In the formulations examined here, upconversion was detected when the laser beam was incident along the edge square of the cuvette sample. The concentration of the sensitizer was chosen with an absorbance of ~ 1 at the excitation wavelength, whereas the acceptor concentration was selected so that it can quench the excited state of the sensitizer at least up to 90 % as extrapolated from Stern-Volmer kinetics (ksv). The power dependence data were plotted as a double logarithmic graph showing the integrated upconverted emission as a function of incident power densities. Quantum Yield Measurements: Upconversion quantum yield of acceptor AnCO2

- or PyCO2

- sensitized by Ru(II) sensitizers were calculated relative to [Ru(bpy)3](PF6)2 (Φstd = 0.018) in aerated spectrophotometric grade acetonitrile under 514.5 nm excitation.7,8 The conditions used to calculate the quantum yield were selected to have optically-dilute samples of sensitizers (A514 nm = 0.1 ~ 0.2) with acceptor concentration appropriate for at least 90 % quenching rate. The fluorescence quantum yield of the water-soluble AnCO2

- and PyCO2

- resulted from direct excitation at 335 nm were calculated relative to anthracene (Φstd = 0.27) in aerated spectrophotometric grade acetonitrile.9 Determination of the triplet decay (kT) and the triplet-triplet annihilation (kTTA): After populating the triplet-excited state acceptors, the triplet decay (kT) and the triplet-triplet annihilation (kTTA) rate constants were determined by fitting the kinetic absorption decay data at 420 nm as a function of time according to Eq.S1. Here, [3M*] is the concentration of the triplet excited state acceptor. Fitting the transient absorption decay data of the triplet AnCO2

- or PyCO2- at 420 nm requires the integration

of Eq.S1 to yield Eq.S2. 10–14

d[ 3M*]

dt= −kT [ 3M*]− kTTA[ 3M*]2 Eq.S1

ΔA =

ΔA0 (1− β )exp(ktt)− β

Eq.S2

β =

kTTA[3 M *]0kTTA[3 M *]0 + kT

Eq.S3

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[3M*] can be translated to transient absorption terms where it is directly proportional to ΔA values. The analytical solution to equate for the fraction of acceptors occurring through the bimolecular TTA channel was designated by β (Eq.S3). To simplify the parameters, α was used, where α= kTTA [3M*]0 and β= α/(kT + α). Using the extinction coefficient of the triplet excited state of AnCO2

- (εT = 39,000 M-1cm-1) or PyCO2- (εT =

21,200 M-1cm-1) (data in Figure S4), a series of kinetic absorption decay data were collected at 420 nm as a function of pulse energy to give kT (s-1), kTTA (M-1 s-1), and the fraction β.

[Ru(bpy)3]2+

ET = 2.1 eV

[Ru(BPS)3]4-

ET = 2.2 eV

AnCO2-

ET = 1.83 eV ET = 2.00 eV

ES = 3.15 eV

PyCO2-

ES = 3.28 eV

Figure S1. Energy levels showing the triplet/singlet energies for the Ru(II) sensitizers and carboxylate acceptors.

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a)  

0 1 2 3

0.0

0.2

0.4

0.6

0.8

1.0

Ru(bpy)32+ + AnCO2

- in H2O

[AnCO2-] (mM) 0

0.24 0.48 0.70 0.91

1.3 1.67

2.0 2.31 2.68 3.02N

orm

aliz

ed In

tens

ity (a

.u.)

Time (µs)0 5 10 15

0.0

0.2

0.4

0.6

0.8

1.0

Ru(BPS)34- + AnCO2

- in H2O

[AnCO2-] (mM) 0 0.49 0.95 1.4 1.82 2.22 2.61

Nor

mal

ized

Inte

nsity

(a.u

.)

Time (µs)

b)  

0 1 2 3

0.0

0.2

0.4

0.6

0.8

1.0

Ru(bpy)32+ + PyCO2

- in H2O

[PyCO2-] (mM) 0 0.49 0.95 1.4 1.82 2.22 2.61

Nor

mal

ized

Inte

nsity

(a.u

.)

Time (µs)

c)  

0 5 10 15

0.0

0.2

0.4

0.6

0.8

1.0

Ru(BPS)34- + PyCO2

- in H2O

[PyCO2-] (mM) 0 0.49 0.95 1.4 1.82 2.22 2.61

Nor

mal

ized

Inte

nsity

(a.u

.)

Time (µs)

d)  

Figure S2. Dynamic photoluminescence quenching of Ru(II) photosensitizers, under optically-dilute conditions in degassed H2O, monitored at 625 nm. a) [Ru(bpy)3]2+ quenched by AnCO2

- b) [Ru(BPS)3]4- quenched by AnCO2- c) [Ru(bpy)3]2+ quenched by PyCO2

- d)

[Ru(BPS)3]4- quenched by PyCO2-.

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0.0 0.5 1.0 1.5 2.0 2.5 3.0

0

2

4

6

8

10

12

14 In H2O Solvent

<KSV>H2O = 2528 M-1

<τ0>H2O = 0.59 µs

<kq>H2O = 4.27 x 109 M-1s-1

<KSV>H2O = 4222 M-1

<τ0>H2O = 588 ns

<kq>H2O = 7.18 x 109 M-1s-1

τ 0/τ

-1

Concentration (mM)

O O- Na+

O

O-Na+

a)  

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0

1

2

3

4

5

6

7

8

9

<KSV>H2O = 1746 M-1

<τ0>H2O = 3.71 µs

<kq>H2O = 4.71 x 108 M-1s-1

<KSV>H2O = 2752 M-1

<τ0>H2O = 3.71 µs

<kq>H2O = 7.41 x 108 M-1s-1

In H2O Solvent

τ 0/τ

-1

Concentration (mM)

O O- Na+

O

O-Na+

b)  

Figure S3. Stern-Volmer plots of samples prepared in degassed H2O solvent. a) [Ru(bpy)3]2+ quenched by AnCO2

- (black square) and PyCO2- (red circles). b) [Ru(BPS)3]4- quenched by

AnCO2- (black square) and PyCO2

- (red circles).

       

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400 450 500 550 600 650

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

∆O.D.

Wavelength (nm)

3*AnCO2-

Ru(BPS)34- + AnCO2

-

Delay time: 0 ns 50 ns 100 ns 250 ns 1 µs

2 µs 5 µs 25 µs 50 µs

400 450 500 550 600 650

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

∆O.D

.

Wavelength (nm)

3*PyCO2-

Ru(BPS)34- + PyCO2

-

Delay time: 0 ns 250 ns 1 µs 2 µs 3 µs 5 µs 7 µs

0 1 2 3 4 5 6 7 8

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

Inte

nsity

Time (µs)

Kinetic growth at 420 nm <k> = 6.4 x 105 s-1

Emission decay at 630 nm <k> = 5.8 x 105 s-1

0 2 4 6 8 10 12 140.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

Inte

nsity

Time (µs)

Kinetic growth at 420 nm <k> = 4.41 x 105 s-1

Emission decay at 630 nm <k> = 4.05 x 105 s-1

B)   B`)  

A)   A`)  

Figure S4. Transient absorption difference spectra of [Ru(BPS)3]4- (A452 nm ~ 0.35) with A) 0.5 mM of AnCO2

- and A`) 0.5 mM of PyCO2- respectively measured as a function of delay

time. B) and B`) show the kinetic growth (blue line) of the sensitized triplet acceptor of AnCO2

- and PyCO2- respectively measured at 420 nm and the quenched emission decay

(black line) of [Ru(BPS)3]4- at 630 nm with each acceptor; the red and pink lines represent the single exponential decay fits. Samples were bubble degassed and excited at 452 nm (~ 3 mJ/pulse).

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Figure S5. Transient absorption kinetic decay of the triplet excited state of AnCO2- (black

line) and PyCO2- (red line) in degassed H2O monitored at 420 nm upon 452 nm excitation.

The conditions were [Ru(bpy)3](Cl2) (3.5 x 10-5 M) with AnCO2- (3.7 mM) and PyCO2

- (3.9 mM) respectively. The triplet extinction coefficient of AnCO2

- (3ε = 39,000 M-1cm-1) and PyCO2

- (3ε = 21,200 M-1cm-1) were averaged as a function of pulse energy and calculated using Eq. S4.12,13,15,16 [Ru(bpy)3](Cl2) in water was used as the donor with an excited state absorption maximum at 370 nm (3ε370 nm = 22,000 M-1cm-1).17 The inset shows the single exponential fit (magenta line) and the residual (green line) of [Ru(bpy)3](Cl2) in water monitored at 370 nm.

0 100 200 300 400

0.00

0.05

0.10

0.15

0.20

0 1 2 3 4

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Kinetic decay at 370 nm Ru(bpy)3

2+ in H2O

ε370 nm = 22,000 M-1 cm-1

∆O.D.

Time (µs)

Kinetic decay at 420 nm Ru(bpy)3

2+ + AnCO2- in H2O

Ru(bpy)32+ + PyCO2

- in H2O

∆O.D.

Time (µs)

(Eq. S4)

3ε Acceptor3εDonor

=ΔAAcceptor

ΔADonor

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Pulse  Energy  (mJ)   ∆A0   kT  (104  s-­‐1)   kTTA  (109  M-­‐1  s-­‐1)   α  (104  s-­‐1)   β  

4.9   0.316   1.89   6.79   5.49   0.744  5.9   0.362   1.88   6.07   5.61   0.749  7.9   0.415   1.84   5.55   5.91   0.763  8.5   0.422   1.89   5.38   5.81   0.754  

Table S1. Parameters Obtained from the Fits of the Transient Absorption Decay Data at 420 nm for the sample containing [Ru(bpy)3]2+ (3.4 x 10-5 M) and AnCO2

- (3.78 mM) in H2O.

0 50 100 150 200

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

∆O.D.

Time (µs)

Kinetic decay at 420 nm

0 50 100 150 200 250 300 350

0.0

0.1

0.2

0.3

0.4Kinetic decay at 420 nmRu(bpy)3

2+ + AnCO2- in water

Pulsed energy (mJ) 8.5 7.9 5.9 4.9 3.9 2.9 1.9

∆O.D.

Time (µs)

a)   b)  

Figure S6. a) Transient absorption decay at 420 nm of 3.4 x 10-5 M [Ru(bpy)3]2+ and 3.78 mM AnCO2

- in degassed water measured as a function of pulse energy. (λexc = 452 nm). b) shows the representative kinetic fit (4.9 mJ/ pulse data) to Eq. S2 (red line), and the residual fit is represented by the green line.

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  AnCO2-­‐   PyCO2

-­‐  Trial  1   0.08395   0.53214  Trial  2   0.06169   0.49899  Trial  3   0.06021   0.5011  Average   0.0686   0.5107  St.  Dev.   0.0132   0.0185  

 

Figure S7. Comparison of the emission intensity for AnCO2- (black line) and PyCO2

- (red line) in water, matched at optically-dilute conditions under 335 nm excitation. Anthracene in acetonitrile with (Φf = 0.27) was used as reference for quantum yield calculations.

380 400 420 440 460 480

0.0

6.0x105

1.2x106

1.8x106

2.4x106

3.0x106

Em

issi

on In

tens

ity

Wavelength (nm)

Anthracene in acetonitrile AnCO2

- in water

PyCO2- in water

Table S2. Quantum Yield Values

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0 2 4 6 8 10 12 14 16 18 20 22 240.0

0.2

0.4

0.6

0.8

1.0

0 200 400 600 800 1000 1200 1400 1600 18000.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

Inte

nsity

(a.

u.)

Time (ns)

[Ru(BPS)3]4- + AnCO2

-

[Ru(BPS)3]4- + AnCO2

- + NaOtf

N

orm

aliz

ed In

tens

ity (a

.u.)

Time (µs)

In degassed water [Ru(BPS)3]

4-

400 450 500 550 600 650 700 750 8000

1E6

2E6

3E6

4E6

5E6

PL

Inte

nsity

(a.u

.)

Wavelength (nm)

[Ru(BPS)3]4-

[Ru(BPS)3]4- + AnCO2

- [Ru(BPS)3]

4- + AnCO2- + NaOtf

a)   b)  

Figure S8. a) Time resolved emission intensity monitored at 630 nm in water for [Ru(BPS)3]4- in with no additives (black line), with 3 mM of AnCO2

- (blue line), and with 3 mM of AnCO2- + 0.3 M of

NaOTf (red line). b) shows the upconverted emission intensity unaffected by the presence of salt in solution.

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