f-element optical and nmr spectroscopy-insights from...

30th Helsinki Winter School in

Theoretical Chemistry

F-element optical and NMR spectroscopy-insights from experiment

and theory

17/12/2014

Optical Spectroscopy 1:

Lanthanides

Louise Natrajan

[email protected]

Pure oxidation state actinide compounds and fundamental chemistry

Transition metal polypyridyls: two photon spectroscopy

Geochemistry of Uranyl

Lanthanide upconverting nanoparticle enzyme biosensors and FRET

Research Themes

Optical Spectroscopy •  X-ray diffraction •  UV-vis-nIR •  Emission •  IR and Raman •  NMR •  EPR •  XAS (EXAFS, XANES)

Recommended reading:

Chemistry of the f-block elements-Helen Aspinall (Gordon and Breach)

The f elements-Nikolas Kaltsoyannis and Peter Scott (Oxford Chemistry Primers)

Principles of Fluorescence Spectroscopy-Joseph Lackowicz (Springer)

Chemical Reviews special edition, 2002, 102, (6), 1805 – 2476.

Useful Properties of the Lanthanides Resulting from the ‘core like’ nature of the f-orbitals:

Catalytic convertors in car exhausts (CeO2)

Lighting-fluorescent lamps

Imaging in medicine: MRI (Gd), luminescent cellular probes (e.g. Eu)

Lanthanide Complexes as Luminescent Sensors and Probes

Applications: • luminescent phosphors: lighting, displays, security encoding

Biological Uses:

• Structural probes (site symmetry, coordination number)

• Analytical probes (determining concentrations of analytes)

• Imaging probes for medical diagnosis e.g. tumour cell imaging Refs. T. Gunnlaugsson et al., Topics in Current Chemistry, 2007, 281, pg. 1- 43.

J. Yuan et al., Journal of Fluorescence, 2005, 15, pg. 559 - 568.

Near Infra-red Excitation/Emission

> 500 microns depth penetration of near infra-red light

3D optical imaging Biological imaging

Yb3+, Nd3+

Photochemistry Re-cap: Absorption of light: Electronic transitions

• organic molecules, metal complexes (high ε)

E

Internuclear separation

ground state

Vertical absorption

excited state Vertical emission (radiative decay)

Kasha’s rule: emission from lowest vibrational (relaxed) state

Vibrational relaxation (VR) Non-radiative de-activation

S0

S1*

Fluorescence-radiative decay between states of the same multiplicity (2S+1)

Photochemistry Re-cap:

E

Internuclear separation

ground State (S0)

excited singlet state (S1*)

S0

Phosphorescence-radiative decay between states of different multiplicity

T1*

excited triplet state (T1*)

Hund’s Rule: for every singlet excited state, there is a triplet state which lies lower in energy

ISC-intersystem crossing (S1- T1): horizonal transition

radiationless process between 2 states of different multiplicity

Spin-Orbit Coupling •  Crossing points occur on the S1 and Tn potential energy curves

•  Application of a magnetic torque to an electron spin can result in a change in spin and a change in angular momentum

• Most common mechanism of ISC

•  Improved with the addition of heavy atoms

El Sayed’s Rule •  Intersystem crossing is slow unless there is a

change in orbital type

More Rules!

Selection Rules Spin Selection rule: ΔS = 0 allowed transition

• Fluorescence S1* to S0, ΔS = 0, allowed, fast decay (ns)

• Phosphorescence T1* to S0, ΔS = 1, forbidden, slow (s)

Electronic transitions in lanthanides-Absorption •  f-f transitions (weak oscillator strengths, ε ~ 1 M-1 cm-1, c.f. d-d transitions ~ 100 and π-π ~ 105) • Laporte selection rules (centrosymmetric cxs (i): Δ l = 1 and g u • f-f Δ l = 0, slow decay results in long lived emission • Relaxation of the Laporte selection rule occurs by spin orbit coupling (l and s) • Described by Russell-Saunders coupling scheme

Example Pr(Tf2N)3 10-2 M in BumimTf2N

0

0.002

0.004

0.006

0.008

0.01

0.012

400 450 500 550 600 650

abso

rban

ce

3PJ

1D2 0

1

2

1I6

Pr3+, 4f2,3H4

0

5

10

15

20

25 E / 103 cm-1

1G4

1D2

3H4

3F

1I6

3P

4 5 6 2 3 4

0 1 2

• Line-like absorption and emission spectra

• Transitions between states derived from Russell-Saunders spin orbit coupling (J)

• Pale colours (formally forbidden transitions)

f-f Electronic Transition Intensities

•  Judd-Ofelt Theory

•  Theoretical oscillator strengths f (J, J’) of the J → J’ transition at the mean frequency ν is given for an electric dipole transition

Only really works for doped solids in high symmetry (e.g. cubic)

Judd-Ofelt Celebration!

Russell Saunders Coupling Electronic structure of the 4f elements

• Each state will have: S overall spin and L overall orbital angular momentum: 2S+1L (d-orbitals)

• spin and orbital angular momentums can couple: 2S+1L J

• J takes values from |L+S|…|L-S|

Spin multiplicity 2S+1, where S = overall spin

Label S P D F G H I J K

L 0 1 2 3 4 5 6 7 8

2S+1L J J = L+S, L+S-1, L+S-2…, |L-S|

Hund’s Rules for Ground State • Spin multiplicity must be the highest possible (Smax) • If more than one term have the highest multiplicity, the term with the highest value of L is the ground state (Lmax)

• The ground level has Jmin if the subshell is less than half full

• The ground level has Jmax if the subshell is greater than half full

Example: Nd3+, f3 Smax = 3/2, 2S+1 = 4

3 2 1 0 -1 -2 -3 ml

l = 3 ! Lmax = 3 + 2 +1 = 6 = I state

J = |L+S|…|L-S| = 12/2 + 3/2, 12/2 + 3/2 -1…12/2 - 3/2

= 15/2, 13/2, 11/2, 9/2 = 4 I9/2

[Xe] 4f 3

4 F

4 I

4 F3/2

4 F5/2

4 F7/2

4 F11/2

4 I9/2

4 I11/2

4 I13/2

4 I15/2

Electronic configuration

Interelectronicrepulsion

Spin-oribit coupling Crystal field

splitting

Higher energylevels

Russell Saunders Coupling: Nd3+ • Transitions from excited state to ground 4IJ ground state

• Series of absorption and emission lines

• Crystal field small-can be observed in some transitions (noteably Nd3+, Yb3+)

Pr3+ (f2): S = 1/2 + 1/2 = 1, 2S+1 = 3

L = 3 + 2 = 5 = H

J = 5+1…5-1, = 6, 5, 4

Ground state = 3H4 3 2 1 0 -1 -2 -3 ml

l = 3 !

4f Emission Spectra •  Line-like emission spectra •  Long lived emission (milliseconds - microseconds) •  Range from UV (Gd3+), to visible (Tm3+, Sm3+, Eu3+,

Tb3+, Dy3+) to near infra-red (Nd3+, Pr3+, Er3+, Yb3+)

L.S. Natrajan, A.N. Swinburne, unpublished results, The University of Manchester, 2013.

Defining the Emissive State •  Energy gap law: emissive state is the one with the

biggest energy gap to the next lowest state

Nd3 +Eu3 + Tb3 +Yb3+ O-H O -DTm3+ Sm3 + P r3+ Er3+

3H 4

4 I13/2

4I1 1/2

3H 4

3H 5

3H 6

3H 6

3H 5

3H 4

0

2 00 00

4 I9/2

4I1 1/2

4I1 3/2

4I1 5/2

4 F3/2

2 H9 /2

4S3 /2

4 F9/2

2H 11 /2

4 G5/2

4 G7/2

4 G9/2

(2 D ,2P)3/2

4G1 1/25D 4

7F 07F 17F 27F 37F 4

7F 5

7F 67F0

7F1

7F2

7F3

7F4

7F5

7F6

5 D0

5D 1

5 D2

2 F5 /2

2 F7 /2

1 00 00

6 H5 /2

6 H7 /2

6 H9 /2

6 H1 1/2

6 H1 3/2

4 F 3/2

4 G5/2

4 F 3/2

4 F 1/2

4 F 5/2

4 F 7/2

4 G7/2

4 F 9/2

4 F 11/2

3 F2

3 F4

3P0

3P 1

3 F3

1I6

1G4

4 I9/2

4F9/2

4S3 /2

4F7/2

3 F4

3 F3

3 F2

1G 4

E /

cm-1

υ=0

υ=1

υ=2

υ=3

υ=4

υ=5

υ=0

υ=1

υ=2

υ=3

υ=4

υ=5

υ=6

υ=7

2H11/2

1D2

• Energy gap = wavelength of emission

• Bigger gap = longer lifetime

• Tb3+ and Eu3+

millisecond lifetimes

• Non radiative quenching can reduce the lifetime e.g. by vibrations

Lifetimes •  It is the average time spent in an excited state before

radiative decay • Given by the equation

•  The intrinsic lifetime is the average time spent in the excited state without non-radiative deactivation processes

•  Units of lifetimes is usually ns

•  The inverse is ns-1 which is a rate

•  The intensity of emission after a pump pulse decays exponentially

•  Taking the natural log of this gives a linear relationship between intensity and time

Lifetimes

• Methods used to measure lifetimes are a statistical methods based on the bulk solution

•  Lifetimes are fitted using least squares regression

•  Exchange processes which occur on timescales faster than the lifetime are averaged out. Exchange processes slower than the lifetime are resolved a separate lifetimes

Time Dependence of Emitted Light

• During this time, a fraction 1/e of the excited molecules return to the ground state (e = 2.73)

0

200000

400000

0 4 8 12

time/microseconds

intensity 1/e I0

t = t

Lifetimes of Ln3+ (τ):

Tb3+, Eu3+ milliseconds

Sm3+, Dy3+, Yb3+, Er3+ microseconds

Pr3+, Nd3+ nanoseconds (10 - 100’s)

I(t) = It = 0.e-kt

• The lifetime of the excited state is given by: τ = 1/kobs (s)

Lifetime Determination from Kinetic Traces

1. Stepwise increase of time delay (manual or software driven)

!Tb3+ complex in water: 0.1 ms steps (0.1 – 10 ms) at 545 nm

L.S. Natrajan, P.L. Timmins, M. Lunn, and S.L. Heath, Inorg. Chem., 2007, 46, 10877−10886.

2. Time Correlated Single Photon Counting (TCSPC)

0.0 5.0x105 1.0x106 1.5x106 2.0x106

0

2

4

6

8

10

τ = 74 microsecondsLn

(Em

issi

on In

tens

ity)

time / nanosecondsSm3+ complex 200 microsecond range at 650 nm: Tail fit

L.S. Natrajan, J.A. Weinstein, C. Wilson, P.L. Arnold, Dalton Trans., 2004, 28, 3748.


3. Photodiode detection with an oscilloscope

!Yb3+ in water, Ge-diode detector, 980 nm, ns/µs timescale; Reconvolution fit with a scatterer

L.S. Natrajan, P.L. Timmins, M. Lunn, and S.L. Heath, Inorg. Chem., 2007, 46, 10877−10886.


Grow-in Component (Rise Time)

•  Grow in exponential fitted before decay-indicates slow energy transfer from sensitiser triplet state to Yb3 emissive excited state (corresponds to emission decay of the organic sensitiser)

•  If different in D2O than H2O, indicates phonon assisted energy transfer is the rate determining step

Yb3+ (D2O) Yb3+ (H2O)

Quantum Yields •  A measure of the efficiency on fluorescence

Integrating sphere

Hypersensitive Transitions

•  Some transitions are sensitive to changes in symmetry and/or the inner coordination sphere.

•  They display shifts in their maxima, splitting and intensity

•  In hypothetical Ln3+, only magnetic dipole transitions are allowed: ΔL = 0, ΔJ = 0, 1

e.g. 5D0→ 7F1 in Eu3+

• In a complex, electric dipole (ED) transitions are induced: ΔL, ΔJ = 0, 2, 4, 6 (0→0 forbidden)

• Some transitions acquire strength by both MD and ED e.g. Tb3+

Hypersensitive transitions-often quadrupolar transitions: ΔJ = 2

e.g. 5D0→ 7F2 in Eu3+

Mechanism: mixing of the 4f states with ligand states

Some Examples: Eu3+

550 600 650 700

Em

isis

onIn

tens

ity /

Arb

. Un.

wavelength / nm

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3ΔJ = 4

550 600 650 700

Em

isis

onIn

tens

ity /

Arb

. Un.

wavelength / nm

FJ}50 →→{ D 7

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3Δ

O

Eu O

OS

O

ButO

But

But

ButO

K

But

But

But

But

O

O

550 600 650 700

Em

isis

onIn

tens

ity /

Arb

. Un.

wavelength / nm

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3ΔJ = 4

550 600 650 700

Em

isis

onIn

tens

ity /

Arb

. Un.

wavelength / nm

FJ}50 →→{ D 7

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3Δ

550 600 650 700

Em

isis

onIn

tens

ity /

Arb

. Un.

wavelength / nm550 600 650 700

Em

isis

onIn

tens

ity /

Arb

. Un.

wavelength / nm

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3ΔJ = 4

550 600 650 700

Em

isis

onIn

tens

ity /

Arb

. Un.


Em

isis

onIn

tens

ity /

Arb

. Un.

wavelength / nm

FJ}50 → FJ}50 →→{ D 7→{ D 7

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3Δ

O

Eu O

OS

O

ButO

But

But

ButO

K

But

But

But

But

O

O

• Eu3+ ion in high symmetry environment

• ΔJ = 1, ΔJ = 2 and ΔJ = 4 transitions strong

• ΔJ = 0 transition very weak

• Eu3+ ion low symmetry environment

• ΔJ = 1 weak

• ΔJ = 0 fairly strong

• ΔJ = 2 very strong

0

0.2

0.4

0.6

0.8

1

500 600 700 800

Wavelength (nm)

No

rm

alised

Em

issio

n I

nte

nsit

y

ΔJ = 1 ΔJ = 2

ΔJ = 3

ΔJ = 4

• Split into two components

Hypersensitive Transitions in Nd3+

780 800 820

2H9/2,4F5/2←4I9/2

Nd(BrO3)3.9H2O (s)

[Nd(H2O)9]3+(aq)

NdCl3.6H2O (s)

CN = 9

CN = 9

CN = 9

Absorption

H2N

N

N

N

N

N N

N

O O

O

O

O

OOO

O

OO O

Nd

Nd

-O

N

NN

N NO

O

O O

O

O

N

N N

O

O

O O

O

O

Nd

Nd

4F3/2 → 4I13/2

Emission

Faulkner et al., J. Am. Chem. Soc., 2009, 131, 9916 – 9917.

Other Transitions: Absorptions •  f-d transitions: allowed by Laporte’s selection rule

Highly energetic except for Ce3+, Pr3+ and Tb3+ (4f to 5d)

225 250 300 nm

[Ce(H2O)9]3+, D3h symmetry

Ce3+ [Xe]5d1 generates two levels, 2D3/2 and 2D5/2 • 4 transitions

ε ~ 800 M-1 cm-1

300

200

100

0 49 47 45 43

ε / M-1cm-1

E / 103 cm-1

Tb

Pr

[Ln(H2O)9]3+

LMCT Transitions

•  Occurs in complexes with ligands that can be oxidised (redox reaction)- Laporte allowed

•  Therefore the metal must have an accessible +2 oxidation state

O NN

CO2-

CO2--O2C CO2

-

O NN

CO2-CO2

--O2CCO2

-Eu3+Eu3+

Ar + Eu3+→ Ar• + Eu2+ Transient Ligand radical + Eu(II)

π-π* ε = 260 M-1 cm-1

LMCT

Natrajan et al., Inorg. Chem., 2007, 46, 10877 – 10866.

Sensitised Emission •  The special case of 4f elements: indirect excitation • In view of weak f-f oscillator strengths, direct excitation (f-f absorption) is inefficient

• Laporte selection rule overcome by the ‘antenna effect’

Organic chromophore: hv1 + Ar → 1Ar* → 3Ar* → Ln* → Ln + hvLn

hv

Light harvesting Energy transfer

hvLn

Light emission 400 500 600 700 800

Wavelength (nm)

S. Faulkner, L. S. Natrajan, W. S. Perry, D. Sykes, Dalton Trans., Perspective Article, 2009, 3890; L.S. Natrajan, Current Inorganic Chemistry, 2011, 1, 61.

Eu β-diketonates

hv

Eu3+

Eu

O

O OO

OO

OO

[Eu(dbm)4][NEt4]

Dbm = dibenzoylmethane

Courtesy of Helen Aspinall, Liverpool University, UK.

Jablonski Diagram Sensitised emission: Energy level scheme

S0

Ligand

Relative Energy(cm-1)

S1

5D0

5D1

5D2

ket

7F0

7F1

7F2

7F3

7F4

7F5

7F6

Eu3+

kfluorescence

kphosphorescence

kbet T1

kisc

• Heavy atom effect -promotes ISC

Competing pathways:

• Ligand fluorescence

• Ligand phosphorescence

• Back energy transfer

Triplet mediated sensitisation path

LMCT Quenching in Eu3+ Complexes

5D0

7FJ

S1

T1

S0

Ligand Eu3+

Relative Energy

kisc

kelectron transferLMCT

Eu2+ + 1Ar*

kelectron transfer

Eu2+

8S7/2

Double electron transfer quenches the Eu3+ emission (NR decay)

• Competitive radiative decays (Eu emission + phosphorescence)

• Non radiative LMCT decay to ground state


LMCT Sensitised Yb3+ Emission

2F5/2

2F7/2

S1

T1

S0

Ligand Yb3+

Relative Energy

kisc

kelectron transfer

LMCTYb2+ + 1Ar*

kelectron transfer

• Alternative mechanism of energy transfer

• Fast energy transfer-mediated via an orbitally allowed transition

• For NIR emitting Ln3+, a wider range of chromophores can be used: e.g.

N

N

ReCl

COOCOC

N

N

N

N N

O

R

Ar(S0)Ln3+→ Ar(S1)Ln3+→ Ar(T1)Ln3+→ Ar•Ln2+→ Ar(S0)(Ln3+)* → Ar(S0)Ln3+


Excitation Spectra Excitation spectrum: Quanta of light emitted at a given wavelength as a function of excitation wavelength; the excitation spectrum follows the absorption spectrum, as the number of photons emitted is directly proportional to the amount of light absorbed.

300 350 400

550 600 650 700

Emis

ison

Inte

nsity

/Ar

b. U

n.

wavelength / nm

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3ΔJ = 4

550 600 650 700

Emis

ison

Inte

nsity

/Ar

b. U

n.

wavelength / nm

FJ}50 →→{ D 7

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3Δ

O

Eu O

OS

O

ButO

But

But

ButO

K

But

But

But

But

O

O

550 600 650 700

Emis

ison

Inte

nsity

/Ar

b. U

n.

wavelength / nm

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3ΔJ = 4

550 600 650 700

Emis

ison

Inte

nsity

/Ar

b. U

n.

wavelength / nm

FJ}50 →→{ D 7

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3Δ

550 600 650 700

Emis

ison

Inte

nsity

/Ar

b. U

n.


Emis

ison

Inte

nsity

/Ar

b. U

n.

wavelength / nm

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3ΔJ = 4

550 600 650 700

Emis

ison

Inte

nsity

/Ar

b. U

n.


Emis

ison

Inte

nsity

/Ar

b. U

n.

wavelength / nm

FJ}50 → FJ}50 →→{ D 7→{ D 7

ΔJ = 0

ΔJ = 2

ΔJ = 1 ΔJ = 3Δ

O

Eu O

OS

O

ButO

But

But

ButO

K

But

But

But

But

O

O

Natrajan et al., Dalton Trans., 2006, 4456.

Excitation (ligand) Emission (f-f)

Nd3+Eu3+ Tb3+ Yb3+0

20000

4I9/2

4I11/2

4I13/2

4I15/2

4F3/2

2H9/2

4S3/2

4F9/2

2H11/2

4G5/2

4G7/2

4G9/2

(2D,2P)3/2

4G11/25D4

7F07F17F27F37F4

7F5

7F67F0

7F1

7F2

7F3

7F4

7F5

7F6

5D0

5D1

5D2

2F5/2

2F7/2

10000

E / c

m-1

3Phen

O-H

υ=0

υ=1

υ=2

υ=3

υ=4

υ=5

Vibrational Quenching by O-X Oscillators

• Ln excited states are quenched by: O-H, N-H and C-H vibrations Nd3 +Eu3 + Tb3 +Yb3+ O-H O -DTm3+ Sm3 + P r3+ Er3+

3H 4

4 I13/2

4I1 1/2

3H 4

3H 5

3H 6

3H 6

3H 5

3H 4

0

2 00 00

4 I9/2

4I1 1/2

4I1 3/2

4I1 5/2

4 F3/2

2 H9 /2

4S3 /2

4 F9/2

2H 11 /2

4 G5/2

4 G7/2

4 G9/2

(2 D ,2P)3/2

4G1 1/25D 4

7F 07F 17F 27F 37F 4

7F 5

7F 67F0

7F1

7F2

7F3

7F4

7F5

7F6

5 D0

5D 1

5 D2

2 F5 /2

2 F7 /2

1 00 00

6 H5 /2

6 H7 /2

6 H9 /2

6 H1 1/2

6 H1 3/2

4 F 3/2

4 G5/2

4 F 3/2

4 F 1/2

4 F 5/2

4 F 7/2

4 G7/2

4 F 9/2

4 F 11/2

3 F2

3 F4

3P0

3P 1

3 F3

1I6

1G4

4 I9/2

4F9/2

4S3 /2

4F7/2

3 F4

3 F3

3 F2

1G 4

E / c

m-1

υ=0

υ=1

υ=2

υ=3

υ=4

υ=5

υ=0

υ=1

υ=2

υ=3

υ=4

υ=5

υ=6

υ=7

2H11/2

1D2

• Limited quenching by O-D oscillators:- (Hooke’s law)

Calculating the Inner Sphere Hydration Number (q)

• Lanthanide coordination compounds are labile: [Ln(H2O)9]3+ + H2O [Ln(H2O)8(H2O)]3+ + H2O

• Use quenching of O-H vs. O-D oscillators to determine q

Horrocks Equation: q = A(kH2O - kD2O-B)

k = rate constant of decay = 1/τ

A, B = proportionality constants

A corrects for inner sphere quenching

B corrects for outer sphere quenching

O H

H

OH

H

O HH

OH

H

OH

H

OH H

OH

H

A and B values have been determined for Eu3+, Tb3+, Yb3+ (Nd3+ and Sm3+)

Horrocks et al., . J. Am. Chem. Soc. 1997, 119, 5972.

Faulkner, et al., Inorg. Chem. Commun. 2001, 187.

Example: [Eu(DTPA)]2-

Q. For the Eu3+ complex determine q:

τH2O = 0.63 milliseconds (ms)

τD2O = 2.60 milliseconds

NN N

O O

O

O O

O O

O O

O

Eu3+

q = A(kH2O - kD2O-B)

A = 1.2 ms

B = 0.25

q = 1.2((1/0.63 - 1/2.60) - 0.25)

NN N

O O

O

O O

O O

O O

O

Eu3+

OH2

→ q= 1.1 ie. one molecule of water is coordinated to europium

Luminescent Chemical Sensors The spectroscopic properties of the lanthanides make them ideal luminescent probes:

• Line like emission spectra: easily identifiable spectral fingerprint • Long luminescent lifetimes • Large Stokes’ shift (Δλ absorption and emission)

Time-resolved luminescence: allows high signal to noise ratios

Time-gating: removal of background fluorescence

time

I em • Allow background fluorescence to decay

• Excite with UV pulse 2 - 4 ms

• Collect Ln3+ emission (Eu, Tb)

Macrocyclic Complexes

• Free Ln3+ ions are toxic to living organisms

• For biological applications e.g. imaging agents, multidentate or macrocyclic ligands are often employed

• Using the chelate effect to create kinetically stable complexes

• Coordinatively saturated complexes- to exclude water molecules from the inner coordination sphere

e.g.

N

NN

NCO2H

CO2H

HO2C

HO2C

N

NN

N

NH2

O

NH2O

H2N

O

H2N O

H4DOTA DOTAM

NN N

OH HO

OH

OH OH

O O

O O

O

H5DTPA

N N

N NN NN N

Ln3+ Luminescence as a Signalling Method

B. Modulation of the energy transfer processes

A. Modification of the Ln3+ inner coordination sphere

• Binding of an analyte switches on or off the Ln3+ emission

• Binding of an analyte reduces O-H quenching and q decreases

Analyte

Analyte

Courtesy of Jean-Claude Bünzli

Example: pH Sensor

N

NN

N

HN

OOO

O

O O

Eu

S

R

O

O

pH 4, q = 1.6

pH 10, q = 0.1

N

NN

N

H2N

OOO

O

O O

Eu

S

R

O

O

OH2

N

NN

NNH

OOO

O

O O

Eu S

R

O

O

H3O+

OH-

Parker et al., J. Am. Chem. Soc., 2001, 123, 7601.

Change in Eu3+ coordination sphere reflected in ratio of hypersensitive transitions

Example: Anion sensors

N N

NNEu3+

O

O

HN

O

O H

H

N

OR

NH

R

NHR

HCO3- N N

NNEu3+

O

O

HN

O

O

N

OR

NH

R

NHR

OHO

- H2O

Bicarbonate sensor-ratiometric probe

Parker et al., Org. Biomol. Chem., 2009, 7,1525.

Lactate and citrate assay

HO O

O OH

O

O

OOO

O

N N

NNH

Eu3+

OHN

O

OH

H

SN

O

NH

CO2-

R

-O2CR

Example: Peptide Conjugates and Targeted Imaging

• Tb3+ complex coupled to a peptidic vector-Tuftsin

• Affinity for macrophage cells

• Targetted probes/imaging agents τH2O = 1.67 ms

τD2O = 3.25 ms

q = 1.2

N N

NN

O

O

O

O

O

O

Tb

HN

O

NH

O

ThrLysProArg

OH2

Faulkner et al., Chem. Commun., 2006, 909.

http://www.youtube.com/watch?v=xcE4VXUgZbY

Electronic configeration Z Element Symbol

Ln LnIII

Ground level

Radius Ln3+ (Å)

eff

cal

58 Cerium Ce [Xe]4f15d16s2 [Xe]4f1 2F5/2 1.061 2.54 59 Praseodymium Pr [Xe]4f36s2 [Xe]4f2 3H4 1.034 3.58 60 Neodymium Nd [Xe]4f46s2 [Xe]4f3 4I9/2 0.995 3.62 61 Promethium Pm [Xe]4f56s2 [Xe]4f4 5I4 0.979 2.68 62 Samarium Sm [Xe]4f66s2 [Xe]4f5 6H5/2 0.964 0.85 63 Europium Eu [Xe]4f76s2 [Xe]4f6 7F0 0.950 0 64 Gadolinium Gd [Xe]4f75d16s2 [Xe]4f7 8S7/2 0.938 7.94 65 Terbium Tb [Xe]4f96s2 [Xe]4f8 7F6 0.923 9.72 66 Dysprosium Dy [Xe]4f106s2 [Xe]4f9 6H15/2 0.908 10.65 67 Holmium Ho [Xe]4f116s2 [Xe]4f10 5I8 0.899 10.60 68 Erbium Er [Xe]4f126s2 [Xe]4f11 4H15/2 0.881 9.58 69 Thulium Tm [Xe]4f136s2 [Xe]4f12 3H6 0.869 7.56 70 Ytterbium Yb [Xe]4f146s2 [Xe]4f13 2F7/2 0.858 4.54 71 Lutetium Lu [Xe]4f145d16s2 [Xe]4f14 1S0 0.848 0

Properties of the lanthanide ions. Note; µeff – the calculated values and show good agreement with experimental values with the exceptions of SmIII (µeff exp = 1.4 -1.7) and EuIII (µeff exp = 3.3-3.5) due to their excited states being close to their ground state.

f-element optical and nmr spectroscopy-insights from...

Documents