スライド 1

Ultrafast transient absorption spectroscopy
of the photo-induced Z-E isomerization
of a photochromic furyfulgide
F. Renth, M. Foca, A. Petter, F. Temps
Chemical Physics Letters 428 (2006) 62-67
Miyasaka Laboratory
Chikashi Ohta
Contents
Introduction
・ Photochromism
・ Photochromism of fulgide
Experiment
Results and Discussion
Conclusion
Photochromism
Photoinduced isomerization
Photoinduced reversible isomerization in a chemical species
between two forms having different color.
(at least, one pathway should be photoinduced.)
hν1
A
Application
B
hν2 or Δ
Basic chemistry
Quick property change
Dipole moment
Determination of a time origin at fs order
Polarizability ・・・・・
Elucidation of the reaction mechanism
Optical device
Factors that dominate the reaction
Photochromism of fulgide
UV
UV
UV
VIS. UV
Z form(1Z)
E-Z isomerization
E form(1E)
C form(1C)
cyclization / cycloreversion
Properties
(1) Three isomers
Z form, E form, C form
(2) Low fatigue
(3)Thermal stability of these isomers
Experimental
The time-resolution of the transient absorption measurement
Pump
detector
T
Sample
Probe
Ti:Sa femtosecond laser system
Excitation : 387 nm
White light: 410 nm ~ 690 nm
Pulse duration : 210 fs
The cyclization and cycloreversion reactions
a few ps
UV
UV
UV
Z form(1Z)
VIS, UV
<1 ps
E form(1E)
C form(1C)
The cyclization from the E form to the C form occurs with a time constant of a
few ps
Reference : J. Phys. Chem. C 2007, 111, 2730-2737
J. Phys. Chem. A 1997, 101, 502 -506
The cycloreversion from the C form to the E form occurs with a time constant
of less than 1 ps
purpose
The dynamics of the Z-E isomerization of the furylfulgide 1Z
Results and Discussion
Transient absorbance of 1Z excited at λ=387 nm
(a) -90 to 90 fs (30 fs interval time)
Excited state of Z form
450 nm
580 nm
Intermidiate state
ΔA / 10-3
(b) 90 fs to 180 fs
(c) 0.18 to 25 ps
Excitation
at 387 nm
Z form
E form
slightly negative signal
Wavelength / nm
the depletion of 1Z due to isomerizaton to the 1E
Time profiles of the transient absorbance of 1Z
ΔA / 10-3
ΔA / 10-3
530 nm
420 nm
220 fs dacay
Z-E photoisomerization reaction
takes place in this time scale
600 nm
4.1 ps decay
The absorption of vibrationally excited
molecules
Time / ps
Excited state τ=220 fs
300 fs
300 fs rise
Intermidiate state
Intermidiate state
4.1 ps
Z form
E form
An oscillatory feature
420 nm
An oscillatory feature
=
600 nm
Time / ps
Quantum chemical
calculations
A vibrational frequency is 57 cm-1
a corresponding torsional mode between
the furan ring and succnic anhydride moity
Z-E photoisomerization
Furan ring
Torsional mode
Succinic anhydride
Z form
E form
60 cm-1
Conclusions
• The transient absorption in the range from λprobe=410 -690 nm was
dominated by a decay on a time scale of 220 fs due to excited state
absorption for all wavelengths.
• A slow component present only at short wavelengths (λprobe<480 nm)
was assigned to hot ground state absorption and decayed with a
time constant of 4.1 ps.
• The observed oscillatory behavior was interpreted as evidence for
vibrational coherence involving a low-frequency torsional mode.
These results indicate that the photo-induced
isomerization of 1Z proceeds on a sub-ps
timescale.
300 fs
4.1 ps
Z form
E form

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