Murakami, M. et al J. AM. CHEM. 2004 , 126, 14764 Miyasaka Lab Tomohiro Kunishi
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Transcript of Murakami, M. et al J. AM. CHEM. 2004 , 126, 14764 Miyasaka Lab Tomohiro Kunishi
Murakami, M. et al J. AM. CHEM. 2004, 126, 14764
Miyasaka Lab
Tomohiro Kunishi
Contents
•Photochromism
•Motivation of the present paper
•Result & Discussion
•Conclusion
Photochromism
Photoinduced reversible transformation in a chemical species between two forms without changes of molecular weight.
AbsorptionRefractive indicesOxidation potential etc
Quick change of physical properties between two isomers
UV light
Vis. lightS S
F2
F2 F2
S S
F2
F2 F2
Motivation
(5) Non-destructive read-out capability with the high sensitivityneeds another conditions arising from the change of the some outer environments that can act as “gate” of the reaction.
(3) Rapid response = (4) high sensitivity = (2) low fatigue
Excited state reaction generally occurs in competition with various processes in a finite lifetime.
Gated-Reaction Control via Multiphoton Laser Pulse Excitation
(1) Thermal stability of both isomers (2) Low fatigue (3) Rapid response (4) High sensitivity(5) Non-destructive readout capability
Optical and Photonic Device
Photochromic Reaction
Open-form
300 400 500 600 7000
1
2
3
4
Ext
inct
ion
Co
effic
ien
t
(1
04 / M
-1cm
-1)
Wavelength / nm
Open-form
Closed-form
Reaction yield from closed-form to open-form is only 1.3% under steady-state light irradiation.
< 360 nm450 ~ 700 nm
Closed-form
Reaction yield: 反応収率
Transient absorption spectra of PT1(c) in n-hexane excited with a 15-ps 532-nm laser pulse.
400 500 600 700 800 900 1000-0.6
-0.4
-0.2
0.0
0.2
0.4
100 ps 10 ps Grnd. state
Abs
orba
nce
(Nor
mal
ized
)
Wavelength / nm
Cycloreversion reaction completed within 100 ps. Perfect recovery of the closed form by UV light after ps 532 nm laser pulse.
400 600 800 1000
-26 ps
80 ps60 ps50 ps
30 ps20 ps10 ps0 ps
100 ps
40 ps
-10 ps
1 ns
Ab
sorb
an
ce (
0.2
/div
.)
Wavelength / nm
Transient absorption: 過渡吸収
Time profile of trasient absorbance
0 50 100 150
0.00
0.05
0.10
0.15
0.20
0 50 100 150-0.6-0.5-0.4-0.3-0.2-0.10.0
(a) 710nm
(b) 580nm
Abso
rbance
Time/ps
0 20 40 60 80-1.5x10-2
-1.0x10-2
-5.0x10-3
0.0
0 20 40 60 80
-4.0x10-2
-2.0x10-2
0.0
0 20 40 60 80
0.0
5.0x10-3
1.0x10-2
1.5x10-2
(c)
(b)
Ab
sorb
an
ce
Time / ps
(a)
Ex. at 540 nm /Mon. at 580 nm
Ex. at 580 nm / Mon. at 620 nm
Ex. at 580 nm / Mon. at 680 nm
10 ps decay / Reaction yield : 1-2 %.No excitation wavelength effect.
Time constant is almost the same.But, remaining absorption is large.
< femtosecond laser > < picosecond laser >
Apparent Reaction Yield
ΦO
0= k0/(kn+ko)
10ps=1/(kn+ko)
hv
Closed isomer Open isomer
S1
kn
S0
ko
Drastic enhancement of the cycloreversion reaction yield.1.3 % (steady-state irradiation) 40 % ( ps 532 nm laser excitation)
Excitation intensity dependence : conversion efficiency at 160 ps after the excitation with a 15-ps 532-nm laser pulse.
0.01 0.1 1
10-2
10-1
100
Co
nve
rsio
n E
ffic
ien
cy
Excitation Intensity (mJ / mm2)
Conversion efficiency-Abs590nm / Abs590nm
Two-photon process is responsible forthe efficient bond breakage.
Slope~2
Conversion efficiency is quadratically in proportion with the exitation intensity
Conversion efficiency: 変換効率
Sn
S0
hv
hv
S1
S0
hv
hv
(1) Simultaneous two-photon absorption process
(2) Stepwise two-photon absorption process
Re-absorption of intermediate speciesThe competition of absorption of lightbetween the ground state molecule and the intermediate species.Effective in the case where the number of total photon is large.
I : Peak Intensity (photon / cm2 sec) δ : 2-photon absorption cross section
Ng : the number of the ground-state moleculesNe : the number of the excited state molecules
2NgINe
Two-photon Absorption Processes
Simultaneous two-photon absorption process : 同時二光子吸収Stepwise two-photon absorption process : 逐次二光子吸収
Comparison of Picosecond and Femtosecond Lasers
Peak Energy Almost the sameTotal photon number PS > FSPeak Energy / Area Size ( ) FS > PS
LASER
Wavelength
Pulse Duration(fwhm)
Output/ Pulse
Peak Energy
Peak Energy/ Area Size
PS 532 nm 15 ps0.5 1.0 mJ
6.7107 W(1 mJ)
7 109
W / cm2
FS540 610 nm
150 fs 5 15 J6.7107 W(10 J)
7 1010
W / cm2
Ratio
Com-parable 1 / 100 1 / 100 1 10
However 1-2 % (reaction yield : FS)
2NgINe I
Two-photon Absorption Processes
Sn
S0
hv
hv
S1
S0
hv
hv
(1) Simultaneous two-photon absorption process
(2) Stepwise two-photon absorption process
Re-absorption of intermediate speciesThe competition of absorption of lightbetween the ground state molecule and the intermediate species.Effective in the case where the number of total photon is large.
I : Peak Intensity (photon / cm2 sec) δ : 2-photon absorption cross section
Ng : the number of the ground-state moleculesNe : the number of the excited state molecules
2NgINe
Simultaneous two-photon absorption process : 同時二光子吸収Stepwise two-photon absorption process : 逐次二光子吸収
Excitation Intensity Dependence ( ps 532 nm laser )
0.0 0.5 1.0 1.5 2.0 2.5 3.00.0
0.5
1.0
At 20 ps
S1
S0 (bleaching)
Excitation Intensity (mJ / mm2)
Ab
sorb
an
ce
400 500 600 700 800 900 1000-0.6
-0.4
-0.2
0.0
0.2
0.4
Ab
sorb
an
ce
Wavelengh/nm
Increase in the S1 population with an increase in the excitation intensity. Further increase of the exc. Intensity decreases the S1 state population, while increasing the So state bleaching. S0
h
S1
Sn
Conclusion
Sn
S1
S0closed form open form
major
minor
0.01 0.1 1
10-2
10-1
100
Co
nve
rsio
n E
ffic
ien
cy
Excitation Intensity (mJ / mm2)
Total photon number PS > FS ↓Stepwise abosorption process PS > FS ↓ Reaction yield PS > FS
Gated-Reaction Control via Multiphoton Laser Pulse Excitation
•Optical memory
Slope~2
Summary
•Picosecond pulsed excitation of the closed-isomer of thediarylethene derivatives led to the drastic enhancement of thecycloreversion reaction.
•this enhancement is attributable to the production of the higher excited state with a large reaction yield of the cycloreversion (50%)Attained via a successive two-photon process.
•A new approach for one-color light control of the gated photochromic system, which can be utilized for an erasable memory system with nondestructive readout capability.