Measurements of the Complete Solvation Response in Ionic Liquid
Sergei Arzhantsev, Hui Jin, Gary A. Baker, and Mark MaroncelliJ. phys. Chem. B 2007,111, 4978-4989
Miyasaka laboratory Satoe Morishima
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Contents
Introduction -Ionic liquid as a solvent - Photo-induced solvation dynamics Femtosecond~nanosecond - Dynamic Stokes shift
Results and Discussion -Kerr-gated emission (KGE) -Time-correlated single photon counting (TCSPC) -Results of time-resolved spectroscopy -Solvation “Mechanism”
Conclusion -Bi-phasic solvation dynamics was observed.
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N NCH3CH2
1-ethyl-3-methylimidazolium( emim+ )
NS S CF3
O
OF3C
O
Obis(trifluoromethylsulfonyl)imide
( TFSI- )
NaCl (m.p. 800 )℃
A molten salt at room temperature constituted from anion and cation.
Ionic liquid is spotlighted as a new type of solvent.
IntroductionExperimentResults &Discussion
ConclusionIonic Liquid
Example
emimTFSI (m.p. -16 )℃
S. Hayashi & h.Hamaguchi, Chem. Lett. 33, 1590-1591 (2004)
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: dipole
rotation diffusion
Solvent Influence IntroductionExperimentResults &Discussion
Conclusion
The solvation ( 溶媒和 ) structure and molecular dynamics of ILs can be different from that of ordinary solvent.
Electric conductivity
Vapor pressure nearly 0
Hard to burn
High viscosity
Biochemistry
Energy device
material
Green chemistry
application
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IntroductionExperimentResults &Discussion
Conclusion
X-rays
UltravioletRays
visible
infrared
Microwaves
Wavelength(m)
10-10
10-8
10-6
10-5
10-2
vibration
Rotation
electronic excitation
Photo-Excitation at UV-Vis Region
IR spectroscopy
Electro magnetic spectrum
HOMO
LUMO
Ground state Excited state
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Detection of Dynamic Stokes Shift
Time-resolved spectroscopy can
directly observe solvation dynamics !
Excited state
h
Ground state
time
IntroductionExperimentResults &Discussion
Conclusion
Energy relaxation
timeBlue Red
Time-scale of solvation in IL:
Femtosecond~nanosecond
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Time-correlated single photon counting (TCSPC) : >20 ps
Femtosecond:
Roughly 50% of the solvation responseis too rapid to be observed by TCSPC ・・・
Picosecond:
TCSPCKGE
10 100 100010.1 (ps)
KGE + TCSPC technique may give us complete solvation
Instrumental Time-Resoluton
IntroductionExperimentResults &Discussion
Conclusion
Kerr-gated emission (KEG) ~450 fs
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Time-correlated single photon counting
TCSPCExperimentIntroduction
Results &Discussion
Conclusion
Light source: Ti: Sapphire laser (SHG)
Exciting λ: 390 nm
System response time : ~36 ps ( FWHM )
Step size: 4 ps
temperature : 295K
t t’
photon
Laser pulse
125 ns time
Co
un
ts
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Kerr-gated emission KGE 2
ExperimentIntroductionResults &Discussion
Conclusion
benzene
Kerr-Gate
benzene
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Sample ExperimentIntroductionResults &Discussion
Conclusion
Solvatochromic probe :Trans-4-dimethylamino-4’-cyanostilbene
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Results of KGE+TCSP
CIntroduction ConclusionExperiment
Results &discussion
htime
Time-resolved emission spectra of DCS in [Im41
+] [BF4-]
Peak shift solvation☞Fast (fs) and slow (ps~ns)
time
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Emission peak shift
Introduction ConclusionExperimentResults &discussion
Sub-ps component:
1 : 100 ~ 700 fs (~20 %)
Dominant slower component
2 : 80 ps ~ 3.0 ns (~80 %)
: 0.3~0.5
Bi-phasic Solvation Function
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Sub-picosecond component
Introduction ConclusionExperimentResults &discussion
Reduced mass( 換算質量 )(R+ + R- ) : Sum of van der Waals radii
There is a reasonable correlation of both f1 and 1 with 1/{±(R++ R-)}1/2
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pico~nanosecond component
Introduction ConclusionExperimentResults &discussion
Time scale of slower component is not directly proportional to viscosity but rather to p (p≈1.2 – 1.3)
D=kT / 6r
Slow components associate with diff
usion??
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Author have presented KGE+TCSPC measurements of the complete solvation response in six ionic liquids using the probe DCS
Observed response functions were found to be biphasic, consisting ofa sub-picosecond component associated with inertial solvent motion And
a dominant “slow” component which is correlated to the solvent viscosity.
Conclusion Introduction ExperimentResults &Discussion
conclusion