Ultrafast Solvation Dynamics of Coumarin 153 in Imidazolium-Based Ionic Liquids

Barnhard Lang, Gonzalo Angulo, and Eric VautheyJ.Phys.Chem.A 2006, 110. 7028-7034

Miyasaka Lab.

Masayasu Muramatsu

Contents

Introduction• Room-Temperature Ionic Liquids• Solvation dynamics

Experimental• Fluorescence up-conversion• Three-pulse photon-echo peak-shift

Results & discussion

Summary

N+

N

N

N-

S S

O

OO

O F

F

F

F

F

F

[cnpmim]+

[Tf2N]-

Room-Temperature Ionic Liquids

Room-temperature ionic liquids (RTILs) are organic molten salts

Ultralow volatility: 揮発性

Flameproof

Electrochemical stability

High viscosity

http://www.chem.eng.osaka-u.ac.jp/~elechem/Research.htm http://www.tuat.ac.jp/~ohno/lab/ionic_liquid/IL.html

Application for the Electron Microscope

Star sand SEM imageIonic liquidleft:with RTIL right:bulk

Solvation dynamics

hν

Solvation in conventional liquids

Ener

gy

Solvation Coordinate

S0

S1

hν

Stabilization

Exited state

Ground state

strongly solvated

通常の有機溶媒

Solvation dynamics

○:anion●:cation

Solvation in ionic liquidsDynamic Stokes-shift

Ener

gy

Solvation Coordinate

S0

S1

Solvation

hνemission

Fluorescence up-conversion

Intensity

time

time

time

delay

Excitation pulse : ωe

Fluorescence : ωf

Gate pulse : ωg

Sum frequency : ωs= ωf+ ωg

0

0

0

sample

BBO

ωe

ωf

ωg

ωs

delay

mono

chr.PMT

ω ｓ = ω ｆ＋ω ｇExitationGate

BBO:β-BaB2O4

monochr: モノクロメーター（分光器） PMT: 光電子増倍管

Three-pulse photon-echo peak-shiftpeak-shift τ’

―:-k1+k2+k3

―: k1-k2+k3

T → large

τ’ → small

3PEPS resultsτ’ vs T

pulse1 makes the coherence of polarization.pulse2 interferes with pulse1 indeced polarization.pulse3 is diffracted as the signal.

τ=0 ： Transient Grating 　　　　　→ 　 no echo

τ 0≫ ： decoherent 　　　　　　　　 → no echo

T 0≫ ： vanish diffraction fringe 　 → no echo干渉縞

Fluorescence up-conversion

Coumarin153 in[cnpmim+][Tf2N-] and[pmim+][BF4

-]

Excitation : 400nmResponse function : 230fs

Dynamic red shift

N+

N

N+

N

N N-

S S

O

OO

O F

F

F

F

F

F

BF4-

[pmim]+

[cnpmim]+ [Tf2N]-

Red : rise Blue : decay

Steady-state absorption and emission spectra

Fluorescence time profiles

× :490nm▼ :540nm● :580nm

× :490nm▼ :540nm● :580nm

Fluorescence up-conversion

Dynamic red shift

Too small peak shift change → ultrafast component?

4600cm-1

600cm-1

500cm-1

Reconstructed time-dependent emission spectra

Time dependence of the emission band maximum

Missing red shift

Three-pulse photon-echo peak-shift

Indocyanine green in[cnpmim+][Tf2N-] and ethanol

Excitation : 800nmPulse duration : 15fs

Differ from Stokes-shift measurements

Inertial part: Signal starts at a higher level and decays slower in ionic liquids

in ionic liquid

in ehtanol

molecular vibration

inertial part

3PEPS results

溶媒の平均自由行程内

分子振動

Summary

The dynamic Stokes shift of coumarin 153 in Room temperature ionic liquids(RTILs) has been measured using fluorescence up-conversion techniques with a response function of 230fs.

Three-pulse photon-echo peak-shift(3PEPS) experiments on indocyanine green in RTILs has been measured.

Ultrafast solvation in RTILs which could not be observed by fluorescence up-conversion was suggested from 3PEPS results. Improved 3PEPS may find farther information.