(1) NMR spectroscopy ( µs, native environment, atomic ...

Experiments to resolve structure and structural dynamics

CO

HO

Structural methods:

(1) NMR spectroscopy (µs, native environment, atomic resolution)

(2) X-ray diffraction (fs, crystals, atomic resolution, destructive)

(3) Vibrational spectroscopy (fs, native environment, atomic resolution)

(4) Nonlinear vibrational Spectroscopy:

information about couplings

(5) Visible (electronic) spectroscopy

(6) EPR spectroscopy

(7) Microscopy

Local vibrational modes are local probes of chemical bonds

Wavelength (in meters)

The Electromagnetic spectrum

Electronic transitions Vibrational transitions nuclear transitions

Spin transitions

λhcE =

Vibrational spectroscopy

C = O

Nuclear motion (vibration) , structural information

Vibrational degrees of freedom

Linear molecule : 3N - 5

General : 3N - 6

Energy : E = hν = hc ν = hc 2134 cm-1 ; 6.4x1013 s-1

)1(8 2 += JJ

cIhE

π22

21

21 rrmm

mmI µ=+

=gas phase :

Schrödinger equation for a diatomic molecule:

)()()(2

22

RERRV Χ=Χ

+∇

µ

V(R) : Potential energy surface


Rotational-Vibrational transitions:

characteristic absorption lines per molecule

frequency position is often known very precisely ~ 0,01 cm-1

narrow linewidths ~ 0.1 cm-1

variety of different absorption lines per molecule

line shapes and intensities are strongly temperature dependent

Abso

rptio

nkoe

ffizi

ent (

cm-1

/Mol

ekül

e/cm

2 )


Rotational-Vibrational transitions:

Potential energy surface V(R) of a diatomic molecule

[ ]2)(1)( eRRae eDRV −−=

eeD

a ωµ2

=

Morse potential

πνω 2=

De : Dissociation energy

Re : Equilibrium distance

Approximation of the Potential energy surface V(R)

+−+−+= 22

2

)(21)()()( e

Re

Re RR

dRVdRR

dRdVRVRV

ee

Taylor expansion of V(R) around Re:

zero

2)(21)( eRRkRV −=

Harmonic oscillator:

νhcnEn )21( +=

HCl En

ergy

µω k

=

Polyatomic molecules

Transformation to 3N-6 normal mode coordinates Qi

3657 cm-1

not IR active

1595 cm-1

IR active

3756 cm-1

IR active

H2O vibrations (gas phase)

∑∑

+==

iiiii

ii QkQQHH 22

21

21)( µ

))cos(1(21)(

21)(

21)( 0

2

00 lkIekEkElI lik ∆+=+=∆ ∆

Monochromatic light source:

Fourier-Transform InfraRed Spectrometer


Polychromatic light source:

νν νπ deBlI li∫∞

∞−

∆−∝∆ 2)()( Interferogram

)()()( 2 ldelIB li ∆∆∝ ∫∞

∞−

∆νπν Spectrum

Removing the constant part of the Intensity trace:

Resolution: max4

3l∆

=∆νAdvantages: more light intensity

multiplexing

stray light suppression


Ratio of this signal with and without sample gives the transmission spectrum T of the sample and -log(T) the absorption.

Lorentian line shape



3657 cm-1

not IR active

1595 cm-1

IR active

3756 cm-1

IR active


∑∑

+==

iiiii

ii QkQQHH 22

21

21)( µ

Spectra-Structure correlations

Infrared spectroscopy is a powerful tool

Polyatomic molecules - Examples

2250 2300 2350 2400 2450 2500 2550 2600 2650 2700 2750

0,0

0,5

1,0

1,5

2,0

pure thioacetic acid 13.9 M 3.98 M 2.32 M 0.34 M 0.14 M

Abso

rban

ce /

OD

Frequency / cm-1

Thioacetic acid in CCl4

1000 2000

0

5

10

pure 13.9 M 3.98 M 2.32 M 0.34 M 0.14 M

Abso

rban

ce /

OD

Frequency / cm-1


3000 35000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

pure 13.9 M 3.98 M 2.32 M 0.34 M 0.14 M

Abso

rban

ce /

OD

Frequency / cm-1


Infrared transitions

In the Born-Oppenheimer approximation the total initial wavefunction is given by:

)(),(),( QQrQr knki ΧΦ=Ψ

k : quantum number of electronic state

n : Quantum number of nuclear state

Q : normal mode coordinates

drdQerQeZM ij l

ljjfif Ψ

−Ψ= ∑ ∑∫ *

dQQQMQM kn

knif )()()( 0

* ΧΧ= ∫ ′

Transition dipole moment Mif for a transition from state i to state f

For a vibrational transition in the same electronic state, k does not change and the integration over dr leads to the permanent dipole moment M0(Q) in the electronic state k. The transition dipole moment vanishes if M0(Q) is constant zero.

Infrared transitions

Vibrational transitions are infrared inactive if the permanent dipole moment M0(Q) does not depend on any change of Q, which can occur on symmetry reasons.

If we expand M0(Q) in a Taylor series around the equilibrium position:

dQQQQQMM nin

i equiif )()( ΧΧ

∂∂

= ∫∑ ′

For harmomic oscillator wavefunction : ∆n = ±1 for vibrational quanta

transition from v=0 (Boltzmann distribution); Overtones (∆v = ±2) are weak

)()0())exp(1(32)( tMMdte

TknVcti

B∫∞

∞−

−−−= ωωπωωα

Absorption coefficient α(ω) is given by the ensemble average of the two-time dipole correlation function:



3657 cm-1

not IR active

1595 cm-1

IR active

3756 cm-1

IR active


∑∑

+==

iiiii

ii QkQQHH 22

21

21)( µ

21

=≈′

=′ D

H

mm

µµ

ωω

Isotope shift for a harmonic oscillator:

same force constant

Fermi resonance

In special cases the strength of overtones or combination bands is enhanced if their energy matches a fundamental transition:

+−±+=± 2

22 4)2(2

21

hV ab

baba ννννν

Theoretical unperturbed bands are shaded and observed bands are

unshaded

Estimation:

Infrared absorption spectra

Contributions to IR band properties

electronic effect: change in the distribution of electrons

cis-trans isomers: higher symmetry in trans isomers -> smaller dipole moments

steric effect: can change force constants e. g. ring strain

solvent effect: shift frequencies

temperature effect: higher T leads normally to lower frequencies and broader bands

polar solvent-solute interaction: can cause dramatically shifts of group frequencies and alterations in band shapes for example: hydrogen bonds

1650 1700 1750 1800 0

1

Abso

rban

ce (a

rb. u

nits

)

0 mM 3 mM 5 mM 10 mM 15 mM 20 mM 30 mM 35 mM 50 mM

C102 in C2Cl4 with different phenol concentrations

hydrogen bonded v(C=O) Not hydrogen bonded v(C=O)

Properties of hydrogen bonds: acceptor modes

~ 30 cm-1 shift of the v(C=O ) upon formation of a hydrogen

bond to lower energies. Reduction of the C=O force

constant due to the hydrogen bond.

Allows a detection of hydrogen bond acceptor modes

E. T. J. Nibbering et al., Israel J. Chem., 39, 1999, 333-346

N O O

C102

Properties of hydrogen bonds: donor modes

Acetic acid dimer in CCl4

Phenol in C2Cl4

Frequency (cm-1) 3500 2000

OH

The infrared band of the donor group (OH) is dramatically and entirely unusual changed upon

formation of a hydrogen bond:

Halfwidth increases

with temperature ~T½.

• Red-shift of ν(O-H) reduced force constant

• Very strong broadening - distribution of bond lengths - anharmonic coupling to low- frequency modes - Fermi resonances - homogeneous broadening

Peculiar bandshape

X H Y -

Q(t)

q(t)

Q(t) X....Y H-bond vibration low frequency ~ 50-350 cm-1 period ~ 100-500 fs

X H Y -

q(t) X-H stretching vibration high frequency ~ 3200 cm-1 period ~10 fs

X H Y -

( )H q Q, = m p 2 ω eff

2 (Q)q 2

m 2 1 2 + P

MM Qlow

22 2

212

+ ω+ , ωeff(Q) = ωhigh + bQ + ...

X H X Y

= + bm q Q mb q Qhighω 2 2 2 212

+pm

m qhigh

22 2

212

+ ω PM

M Qlow

22 2

212

+ ω

anharm. coupl.

+

Anharmonicity of hydrogen bonds: donor modes

Bond length of hydrogen bonds

The spectral position of the hydrogen bonded v(OH) vibration indicates the hydrogen bond length and its strength

strong weak free medium

distribution

Types hydrogen bonds

2000-2500 ; > 3 ; 200 ;

1500-2000 ; > 30 ; 2000 ;

1000-1500 ; ~ 30 ; 1000-1500 ; 1.1

300-1000 ; 10-15 ; 500 ; 1.3

100-300 ; 5-10 ; 100-300 ; 1.4

0 ; 1 ; 10 ; 1.41

∆-freq. Width rel. Intensity ∆-isotop

Ultrafast nonlinear infrared spectroscopy

How can we distinguish between Fermi resonances and low-frequency modes? How strong and relevant are the influences of each coupling?

Infrared Pump/Probe Setup:

Folding of two functions

Ultrafast infrared pump-probe measurements

• No spectral diffusion

• Spectral width of holes: T2OH ≥ 180 fs

(CH3COOD)2

2 1’

0’

1

0

~ 0.6 ps

~ 15 ps

(CD3COOH)2

hot molecule cold molecule

red shifted

blue shifted

Excited state of the O-H stretching vibration

Excited state lifetime (ν=1): 200 fs oscillation frequency ~ 160 cm-1

Where does the energy go? What is the relaxation channel?

(CH3COOD)2 : Total signal Oscillatory component

• Pronounced beating pattern indicate two different oscillation frequencies

• Damping of the oscillations: Dephasing times of about 1 ps

Time - resolved pump-probe signals

(CH3COOD)2 :

K. Heyne et al., Chem. Phys. Lett. 369 (2003) 591-596

Polarization interference; anharmonic and Davydov coupling

Frequency

A

ω0

2V0

Ω

No oscillations due to excitonic coupling:

∆AP P

EvQ vQ

pr

( ) Im[( ) ( )

( )]

( ) ( )

ω ωω ω

ω∝ −

+= =03

13

Oscillatory signals from mixed dimers

No excitonic coupling.

Single O-H

Single O-D

CDO

O H O

OC CHH C3 3

CDO

O H O

OC CHH C3 3

Identical oscillations.

Dephasing of Coherent O-H Stretching Excitations

CHO

O H O

OC CHH C3 3

2-pulse photon echoes: T=0.

CDO

O H O

OC CHH C3 3

No excitonic coupling

Excitonic coupling

Recurrencies


CDO

O H O

OC CHH C3 3

Simulations with one (dash-dotted line) and two (solid line) low-frequency modes and measured data (dots)


CDO

O H O

OC CHH C3 3

Multi-level character of O-H stretch-ing excitation results in multi-level coherences:

• Quantum beats due to anharmonic coupling to low-frequency modes

• Less relevant: Polarization interfe- rences due to excitonic coupling.

Simulations: density matrix approach (sum over states)

O-H stretching mode (T2=200 fs) + 2 low-frequency modes 50,150 cm-1

(T2=1 ps)

O-H stretching mode + 1 low-frequency mode at 50 cm-1

O-H stretching mode

(CH3COOD)2 : Total signal Oscillatory component

• Pronounced beating pattern indicate two different oscillation frequencies

• Damping of the oscillations: Dephasing times of about 1 ps

Time - resolved pump-probe signals

(CH3COOD)2 :

K. Heyne et al., Chem. Phys. Lett. 369 (2003) 591-596

Raman-active low-frequency modes

τbg methyl torsion γbg dimer oop wagging

δag dimer ip bending νag dimer ip stretching

Origin of the coherent oscillations

(CD3-COOH)2 (CH3-COOD)2

τbg γbg

δag νag

Fermi resonance

δ(OH) ν(OH)

ν(OH) δ (OH) ν =0

ν =1 δ = 2

δ = 1

δ = 0 ν(OH) δ (OH)

ν = 0

(ν,δ) =(1,2)

δ = 1

δ = 0

What is the role of the OH bending mode for intra- and intermolecular vibrational energy redistribution? Is there an impact of Fermi resonances on the dynamics? 2xδ

Coupling to O-H bending and C-O stretching modes

Excite O-H stretch (νex=2980 cm-1)

Probe δ(OH) and ν(C-O).

• Perturbed free induction decay on δ(OH) and ν(C-O) fundamen- tals.

• Similar rise of bleaching and enhanced absorption.

Coupling to O-H stretching mode.

C H O

O H O

O C CD D C 3 3

Perturbed free induction decay: T2'≈ 500 fs

Lifetime v=1 state T1=250 fs

Vibrational cooling Tr ≈ 15 ps

Direct O-H bending excitation

No indication of transient v≥1 populations of OH bending mode.

Our picture:

Red-shift of OH bend by excitation of other anharmonically coupled modes. Early times: O-H stretch. Late times: other (low-frequency) modes.

v=0 v=0

v=1

v=1

v=2

OH stretch OH bend

pump probe

Coupling to O-H bending and C-O stretching modes

Fermi resonance coupling

νbuC−O

νbuC=O

δbuO-H

δbuCH3

IR

νagC−O

νagC=O

δagO-H

δagCH3

Raman

Intramolecular H-bond in PMME

3000 2500 2000 1500

0,0

0,5

1,0

0,0

0,5

νO-D

Abso

rban

ce (O

D)

δO-H

νC=O

Wavenumber (cm-1)

νO-H

Abso

rban

ce (O

D)

δO-H

Abso

rban

ce (O

D)PMME: Phthalic acid monomethyl ester

γHB

O-H stretch dynamics of a medium strong H-bond

0 1000 2000 3000

-3

-2

-1

0

1 3200 cm-1

2800 cm-1

Chan

ge o

f Abs

orba

nce

(mO

D)

Delay times (fs)

2600 cm-1

3600 3200 2800 2400 20000,0

0,1

0,2

0,3

Abso

rban

ce (O

D) PMME in C2Cl4

v = 0

v = 1

v = 2

v‘ = 0

v‘ = 1

cold molecule hot molecule

vibrational population

decay

νOH vibrational cooling

< 250 fs

~ 10 ps

Madsen et al., Bull. Chem. Soc. Jpn., 75, 909 (2002)

Low-frequency vibration

Excited state O-H stretching vibration dynamics

0 1000 2000

0,0

0,5

1,0

150 100 500,0

0,5

1,0

Delay Time (fs)

Wavenumbers (cm-1)

A F (no

rm.)

Chan

ge o

f Abs

orba

nce

(mO

D)

3500 3000 2500 20000,0

0,1

0,2

Abso

rban

ce (O

D)

Frequency (cm-1)

Pmme-H in CCl4 pump pulse probe pulse

νOH V = 0

V = 1

V = 2

v = 1 state of the νOH decays with 200 ± 80 fs

coherent oscillations modulate the excited state dynamics with 100 cm-1

200 fs

Pump-probe experiments on PMME

I. excite νOH ; probe δOH

II. excite δOH ; probe δOH

3000 2500 2000 1500 10000,0

0,5

1,0

Abso

rban

ce (O

D)Frequency (cm-1)

Pmme-H in CCl4

δOH νOH νCO



II. excite δOH ; probe δOH

III. excite νCO ; probe δOH

Transient difference spectra

1440 1420 1400 1380 1360 1340 1320-1,2

-0,8

-0,4

0,0

0,4

0,8

Excitation at 1390 cm-1

02 09 03

Abso

rban

ce C

hang

e (m

OD)

Delay times (fs): 140 200 400 800 1600 10000

1440 1420 1400 1380 1360 1340 1320-4

-3

-2

-1

0

1

2

3

4


28.08.03

Chan

ge o

f Abs

orba

nce

(mO

D)

Frequency (cm-1)

Delay times (fs): 140 200 400 800 1600 10000

Spectral region of the δOH and δCH3 absorption bands after excitation of the νOH (I), δOH (II) and νC=O (III) vibrations

(I)

(II)

(III)

Similar dynamics for excitation (I) and (II)

Fast component around 1415 cm-1 and 1390 cm-1 in (III) is missing

1440 1420 1400 1380 1360 1340 1320

-1

0

1

15.10.03


Abso

rban

ce C

hang

e (m

OD)

Frequency (cm-1)

Delay times (fs): 140 200 400 800 1600 10000

δOH δCH3

Dynamics at selected frequency positions

0 1000 2000

-1,4

-0,7

0,0

0,7

1415 cm-1

Abso

rban

ce C

hang

e (m

OD)

Delay Time (fs)

1390 cm-1

0 10000 20000

-0,7

0,0

0,7

1415 cm-1

Abso

rban

ce C

hang

e (m

OD)

Delay Time (fs)

1390 cm-1

νOH (I)

Ο δOH (II)

νCO (III)

negative and positive signals exhibit exhibit similar dynamics cooling of the δOH with about 7± 1 ps

v = 1 decay of the δOH with 800 ± 100fs

Perturbed free induction decay PFID with 550 fs ~ 19 cm-1 (18 cm-1 linewidth) upon νCO excitation only cooling after δOH and νOH excitation population of the v = 1 of the δOH vibration More than 30% of the δOH v = 1 level is populated after νOH excitation

Efficient energy relaxation channel PFID

7 ps 800 fs

Energy relaxation in PMME

δOH νOH

200..300 fs

δ‘OH

800 fs

7 ps

Energy is redistributed from the OH stretching vibration over the OH bending vibration into lower energy modes

Energy relaxation channel from νOH involving the δOH v = 1 state is very efficient

Heyne et al. (2004)

Quantum chemistry calculations – model system

γOH2 = 682 cm-1 γOH1 = 785 cm-1

γHB = 39 cm-1 δOH = 1446 cm-1 νOH = 3279 cm-1

2 2 1+1

2 +1 1+1+1 2+1

2

O-H stretching vibration

(0,1,2,0) (0,1,1,1) (0,1,0,2)

(0,1,1,0) (0,1,0,1)

(0,0,2,0) (0,0,1,1) (0,0,0,2)

(0,0,1,0) (0,0,0,1)

(1,0,0,0)

(0,0,0,0)

(0,1,0,0)

(0,2,0,0)

fsIVR 170=τ

O-H bending vibration

(0,0,2,0) (0,0,1,1)

(0,0,0,2)

(0,0,1,0) (0,0,0,1)

(0,0,0,0)

(0,1,0,0)

fsIVR 750=τ

Part III

CARS and SRL microscopy

CARS: Coherent Anti-Stokes Raman Scattering SRL: Stimulated Raman Loss; modulate ωs, detect ωp

Structural dynamics measured with time-resolved VIS/IR spectroscopy

2,49 Å

2,72 Å

Photoactive Yellow Protein (PYP)

Acetic acid dimer (HAc)

Electronic excited state

Electronic ground state

Ultrafast pump-probe spectroscopy

pump-probe signal reference signal

pump

reference probe

Sample

Ultrafast pump and probe pulses

Ensemble of molecules in solution

S0

S1

S2

no excited state absorption

ground state absorption

excited state absorption (+)

reduced ground state absorption (-) stimulated emission (-) product absorption (+)

VIS – pump VIS – probe experiments

oscillation period: 58 fs ; 567 cm-1

• dynamics of electronic transitions

• S0→S1; S1→S2 and S1→S0; P0 →P1…

• strong overlapping of broad bands

• no direct structural information

• very sensitive to solvent dynamics (stokes shift)

Wavepacket excitation due to spectral broad excitation pulses

coherent oscillations show Raman transitions coupled to the electronic transition

1000 cm-1 ≈ 15 fs or shorter

fingerprint vibrations 1000 .. 2000 cm-1

Proteins are the workhorses of the cell

126 amino acids 1 chromophore

Optimized by evolution Specific geometry of the light absorbing molecule and protein surrounding

Femtosecond experiments in proteins

Only local structure changes on a picosecond time scale

Sapphire plate

BBO

Delay

BBO

λ/2

AgGaS2

DFG

Ti:Sa CPA, 800 nm 1kHz, 50 fs

UV / VIS:

470-760 nm; 1-5 µJ ; 30 fs

Mid-IR:

3-12 µm ; 1-5 µJ ; 100 fs

Light driven proton pump

Halobacterium salinarium

Protein in the purple membrane is bacteriorhodopsin (bR) The chromophore in bR is Retinal

N HR

13-cis

HN R

all-trans

hν

Luecke et al., Science 286, 1999

J 500 fs

3 ps

The light driven proton pump bR

Heyne et al.,J. Phys. Chem. B 104, (2000) 6053

Counterion of the chromophore:

Asp85 (D85)-,

Asp212 (D212)-,

Arg82 (R82)+

Chromophore binding pocket of bR

0 5 10 15

0,0

0,4

0,8

1,2

Transients in the excited state at 480 nm

bR - R82A bR - wt

0,52 ps

1,7 ps and 6,4 ps

norm

aliz

ed a

bsor

ptio

ndi

ffere

nce

time / psFig. 4: Decay of the electronic excited state of bR-wt and R82A;excitation at 580 nm.

R82A Wild-type, R82A/G231C

Changes of the geometry and charge

of the counterion optimize / deoptimize

the primary photoreaction

C-C stretching vibrational marker modes

J. Herbst, K. Heyne, R. Diller, Science, 297, (2002) 822.

Isomerization reaction dynamics

product yield decay times

bR 13-cis 65% 500 fs

Retinal 11,13-cis 26% 2 ps, 7 ps

Reaction optimization in the protein

1200 1180 1160-6

-4

-2

0

2

abso

rban

ce ch

ange

/ m

OD

wavenumber /cm-1

time / ps 0 0.5 0.75 1 6

(bR) 13-cis all-trans

-2 -1 0 1 2 3 4 5 6-8

-6

-4

-2

0

2 B

time / ps

τ = 1.06 ps

τ = 0.51 ps

diffe

renc

e sig

nal /

mOD

1515 cm-1

1529 cm-1

-2 -1 0 1 2 3 4 5 6-5-4-3-2-10123 C

time / ps

τ = 1.01 ps

τ = 0.43 ps

1185 cm-1

1202.5 cm-1

diffe

renc

e sig

nal /

mO

D

-2 -1 0 1 2 3 4 5 6-8

-6

-4

-2

0

2 B

time / ps

τ = 1.06 ps

τ = 0.51 ps

diffe

renc

e sig

nal /

mOD

1515 cm-1

1529 cm-1

-2 -1 0 1 2 3 4 5 6-5-4-3-2-10123 C

time / ps

τ = 1.01 ps

τ = 0.43 ps

1185 cm-1

1202.5 cm-1

diffe

renc

e sig

nal /

mO

D

Structural dynamics measured with time-resolved VIS-IR spectroscopy

2,49 Å

2,72 Å

Photoactive Yellow Protein (PYP)

Electronic excited state

PP*

I0

I0‡

I1

I1'

I2

I2'

~ 2 ms 3 ps

220 ps

3 ns

< 220 µs

~ 260 ms

200 µs

40 %

60 %

λexc = 445 nm

PP*

I0

I0‡

I1

I1'

I2

I2'

~ 2 ms 3 ps

220 ps

3 ns

< 220 µs

~ 260 ms

200 µs

40 %

60 %

PP*

I0

I0‡

I1

I1'

I2

I2'

~ 2 ms 3 ps

220 ps

3 ns

< 220 µs

~ 260 ms

200 µs

40 %

60 %

λexc = 445 nm

–O

SR

O–O

SR

O

SR

– O

O

1

2

3

45

6

7

89 S

R

– O

O

1

2

3

45

6

7

89

P state I0 stateE. D. Getzoff et al., Nat. Struct. Biol. 10, 663 (2003).

hν

Negative phototaxis

Photoreceptor Photoactive Yellow Protein

-1

0

1700 1600 1500 1400 1300 1200 1100 1000

-4

-2

0

2

Abso

rban

ce C

hang

e (m

OD)

Frequency (cm-1)

Delay time (ps): 0.4 0.7 1 2 5 10

PYP after excitation at 450 nm; time resolution ≤ 230 fs

K. Heyne et al. J. Am. Chem. Soc. 127, (2005), 18100-18106

Difference spectra

C8-C9 Vibrational marker modes of PYP

A. Usman et al. Chem. Phys. Lett., 401 (2005) 157

Isomerization reaction

1080 1040 1000-2

-1

0

abso

rban

ce d

iffer

ence

/ m

OD

wavenumber / cm-1

0.4 ps 1.0 ps 2.0 ps 5.0 ps 20 ps

trans cis

product yield decay times

PYP cis 40% 3 ps

PCT cis 5% 10 ps

Protein optimizes the photoreaction

µVIS µVIS

µIR

µIR

1340 1360 1380 1400 1420 1440 1460-3

-2

-1

0

1

2

Chan

ge o

f Abs

orba

nce

(mO

D)

Frequency (cm-1)

Delay time (fs): 400 500 800

18° 18° 32°

linear polarized light

photoselection Θ

Θ1 Θ2

Parallel polarized

Perpendicular polarized

0 20 40 60 800,5

1,0

1,5

2,0

2,5

3,0

Dich

roic

ratio

D=D

par/D

per

Angle Θ

Θ−Θ+

= 2

2

cos2cos21D

The relative angle allows to distinguish:

• Ground state bleachings

• Hot ground states

• Excited states

• Product states

Polarization resolved fs IR-spectroscopy

parallel polarized probe pulse ; perpendicular polarized probe pulse

84±6°

84±6°

26±6°

31±5°

23±5°

23±9°

69±10°

Polarization resolved transients

Isomerization reaction within 3 ps (10 ps in solution)

Quantum yield of 40 % (less than 5% in solution)

Geometry of the first product state I0 is planar

Orientation of the v(C=O) vibration of Glu46 is conserved in the primary process

Initial state P First product state I0

A. Usman et al. Chem. Phys. Lett., 401 (2005) 157 K. Heyne et al. JACS, 127 (2005) 18100

Structure changes in real time

Isomerization reaction within 30 ps

Overall quantum yield of 12 % (depending on structural finetuning)

Geometry of the first product state Lumi-R is ZZEsss

Orientation of the v(C19=O) vibration ring D changes in the electronic excited state

Initial state Pr form First photoproduct Lumi-R

Structure changes in real time

C19=O

A A

B B

C C D D

C19=O

x

y

Chlorophyll a

Qy Photosystem I

Jordan, P., et al., Nature 411, (2001), 909

Chromophore of photosynthesis

Chlorophyll a in toluene

Qy

Experiments and calculations give an angle of ±20° to the y-axis No precise determination of the Qy orientation

x

y

Chlorophyll a

Qy

Chlorophyll a

1800 1600 1400 1200 10000

20

40

60

80

100

120

Abso

rptio

n (m

OD)

Wavenumber (cm-1)

IR absorption of Chl a Chl a transients

PFID: Γ = 9.9 ± 0.5 cm-1

Linewidth of 9 ± 1 cm-1

Angle of the bleaching band: 47 ± 6°

Exhaustive search analysis

99 % range: 35.2°, …, 60.3°

PFID τ = 1070 ± 50 fs

1288 cm-1

1275 1280 1285 1290 1295

-1,0

-0,5

0,0

0,5

Abso

rban

ce C

hang

e (m

OD)

Wavenumber (cm-1)

parallel perpendicular

Pump-prope experiments on the Qy transition

1680 1700 1720 1740 1760

-8

-4

0

4

Abso

rban

ce c

hang

e (m

OD)

Wavenumber (cm-1)

parallel perpendicular

Decay associated spectra

Angle of the bleaching bands, 99% range:

1698 cm-1: 29.8°, …, 36.7°

1739 cm-1: 26.3°, …, 65.8°

1698 cm-1

-20 0 20 40 60 80 100-8

-6

-4

-2

0 parallel perpendicular

Abso

rban

ce c

hang

e (m

OD)

Delay time (ps)

τ1 = 87 psτ2 = 5 ns

Angles of the carbonyl vibrations

Chl a transients

Symmetric v(C=O)s stretch vibration

DFT calculation with Gaussian 03 (basis set: B3lyp/6-31G*)

Calculation of the vibrational modes

34°

34°

29°

34°

29°

51°

Symmetrische v(C=O)s 32…54° Asymmetrische v(C=O)as 29…37° Ringschwingung v(C=C) 35…51°

Symmetric v(C=O)s: 26.3°…65.8°

Symmetrische v(C=O)s 32…54° Asymmetrische v(C=O)as 29…37°

Zusammenhängende Lösungsvolumen

Qy transition dipole moment

34°

34°

29°

34°

29°

51°

Symmetrische v(C=O)s 32…54° Asymmetrische v(C=O)as 29…37° Ringschwingung v(C=C) 35…51°

Symmetric v(C=O)s 26.3°…65.8° Asymmetric v(C=O)as 29.8°…36.7°

Zusammenhängende Lösungsvolumen



34°

34°

32°

34°

32°

51°

Symmetric v(C=O)s 26.3°…65.8° Asymmetric v(C=O)as 29.8°…36.7° Ring vibration v(C=C) 35.2°…60.3°

connected solution area

Symmetric v(C=O)s 26.3°…65.8° Asymmetric v(C=O)as 29.8°…36.7°



Angle to the x-axis: 78° ± 3°

Angle to the y-axis: 12° ± 3°

Angle to the z-axis: 86° ± 2°

New input for energy transfer calculations in photosystems

Compare results with tdm calculations

Orientation of the Qy tdm

Linke, M., et al., JACS, 130, (2008), 14904-14905

Properties of Al-corroles

-20 0 20 40 60 80 100-8-6-4-202468

abso

rban

ce c

hang

e (m

OD)

delay time (ps)

parallel polarization 1522 cm-1

parallel polarization 1515 cm-1

perpendicular polarization 1522 cm-1

perpendicular polarization 1515 cm-1

1506 1512 1518 1524 1530 1536-8-6-4-202468

0 ps parallel polarizationperpendicular polarization


abso

rban

ce c

hang

e (m

OD)

wavenumber (cm-1)

excitation at 620nm

480 520 560 600 640 680 7200.0

0.2

0.4

0.6

abso

rban

ce/e

miss

ion

inte

nsity

/a.u

.

wavelength (nm)

Absoption spectra of Al(tpfc)(py)2 Emission spectra of Al(tpfc)(py)2

absorption and corresponding emmission spectra of Al(tpfc)(py)n in Toluol

Spectral shifts with 2nd pyrrole ligand

C=C stretching band shows dichroism

Relative between electronic and vibrational tdm: 35°

Absorption spectra of Al-corroles

excitation at 580nm

1506 1512 1518 1524 1530 1536-8-6-4-20246

abso

rban

ce ch

ange

(mOD

)

wavenumber (cm-1)

0 ps parallel polarization perpendicular polarization


-20 0 20 40 60 80 100-8-6-4-20246

abso

rban

ce ch

ange

(mOD

)

delay time (ps)

parallel polarization 1523cm-1

parallel polarization 1514cm-1

perpendicular polarization 1523cm-1

perpendicular polarization 1514cm-1

1460 1480 1500 1520 15400,0

0,1

0,2

0,3

0,4

0,5

450 500 550 600 650 7000,0

0,5

1,0

1,5

Al(tpfc)(py)2 in Toluol

abso

rban

ce (O

D)

wavenumber (cm-1)

abso

rban

ce/ a

.u.

wavelength (nm)

Al(tpfc)(py) pump beam 590nm pumobeam 580nm

C=C stretching band at 1520 cm-1

C=C stretching band shows no dichroism

Relative between electronic and vibrational tdm: 54°

Two different electronic states

Angle of electronic transition dipole moments: ~ 90°

Impact on energy relaxation processes

Orientation of the Q tdms

(1) NMR spectroscopy ( µs, native environment, atomic ...

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