シアニン色素の多光子退色反応機構の解明

シアニン色素の
多光子退色反応機構の解明
神戸大学
冬木正紀、和田昭英
Cyanine dye
Photosensitive pigment
Intensive studies for a century
! Geometric structure
! Electronic structure
Absorbance
4
S1←S0
3
2
1
ICG (indocyanine green)
0
500
600
700
800
Wavelength / nm
Low quantum yield of photoreaction from S1: ~10-5
900
[Gratz et al. (1999)]
photodetector for specific cancers [Sugie et al. (2010)]
Multiphoton reactions under fs irradiation
leuco-form
Transient absorption
CH3
CH3
Pump pulse: 800 nm, 70 fs, 40 mJ/cm2
Pump-probe delay: 2.5 ns
CH3
CH3
+
N
pump
N
saturation of
C=C bonds
SO3Na
SO3Na
[Holzer et al. (1998)]
0.0
SO3Na
-0.3
A
N
CH3
-0.6
CH3 CH3
CH3
+
N
[M. Fuyuki et al. (2013(1))]
-0.9
500
600
700
800
Wavelength / nm
900
SO3Na
cis-isomer
ioni
-zation
NIR pump fluence dependence
0.1
A
0.01
leuco-form
slope = 2.9
(560 nm)
cisisomer
(new)
1E-3
1E-4
cis-isomer
slope = 3.9
(890 nm)
leucoform
(new)
[M. Fuyuki et al. (2013(1))]
1E-5
1
10
2
NIR fluence / mJ / cm
one-photon process:
buried in multiphoton process
60
conve
ntional
[9]
Quantum yield: higher electronic state >> S1
Today’s topic: Reaction dynamics of photodegradation
conve
ntional
[9]
Experimental setup（transient absorption）
water flow cell
f=100 mm
probe pulse
(white light continuum)
f=150 mm
delay stage
regenerative
amplifier
800 nm
70 fs
1 mJ
1 KHz
f=250 mm
pump pulse
chopper
sample
f=500 mm
wave plate
(magic angle)
PC
monochoromator
Lock-in amplifier
photomultiplier tube
Cyanine dye in ethanol:
0.6 mM
Thickness of jet:
0.2 mm
Spot size:
pump 0.2 mm
probe 0.1 mm
Probe pulse
Sample jet
[Fuyuki et al. 2010, 2011, 2013]
Transient absorption spectra
1 pump – 1 probe measurement
NIR pump fluence = 50 mJ/cm2
Excited state absorption (ESA) [Meyer et al. (1998)]
0.5
0.0
A
-0.5
-1.0
-1.5
-2.0
-2.5
Probe Delay
0.0 ns
0.5 ns
1.0 ns
1.5 ns
2.0 ns
2.5 ns
500
600
700
800
Wavelength / nm
ESA
S2
S1
PB
900
Photo-bleaching (PB) of trans-isomer
[Philip et al. (1996)]
S0
0.46 ns
trans isomer
[Ashworth et al. (1996) ]
NIR pump fluence dependence
1
-1
10
slope =
2.0
-2
|A|
10
-3
10
slope= 3.0
photobleaching
leuco forms
cis isomers
-4
10
-5
10
1
slope = 3.9
10
2
NIR fluence / mJ / cm
50
Main photodegraded species were ICG fragments.
Photoproducts vs photobleaching
Ratio of |A|
0.09
0.06
3 photon
leuco forms
vs photobleaching
cis isomers
vs photobleaching
0.03
4 photon
0.00
0
10
20
30
2
NIR fluence / mJ / cm
40
Optical order of photodegradation changed from 2 to 4.
Steady state spectra
Absorbance
3
2
NIR irradiation time
00 sec
20 sec
40 sec
80 sec
Pump pulse: fs NIR pulse
(800 nm, 70 fs, 10 mJ/cm2, 1 KHz)
1
0
400
500 600 700 800
Wavelength / nm
900
ICG fragment
cleavage of carbon double
bonding chain
Multiphoton reaction paths of ICG/ethanol
[Fuyuki et al. (2010-2013), Ashworth et al. (1996), Gratz et al. (1999) ]
Temporal profile of photobleaching
1.2
Experiment
Model
decay 1 (485 ps)
decay 2 (14 ps)
decay 3 (1.4 ps)
-A (785 nm)
0.9
0.6
0.3
0.0
0
500
1000
1500
Pump-probe delay / ps
2000
1.2
Experiment
Model
decay 1 (485 ps)
decay 2 (14 ps)
decay 3 (1.4 ps)
-A (785 nm)
0.9
0.6
0.3
0.0
0
10
20
30
40
Pump-probe delay / ps
50
The profile includes 3 exponential decay components.
Assignment
Decay components 1 and 3 correspond to
relaxations in trans singlet system.
14ps time constant corresponds to photofragmentation.
Assignment
Decay components 1 and 3 correspond to
relaxations in trans singlet system.
14ps time constant corresponds to photofragmentation.
Conclusions
fs超短パルス照射下におけるICGの退色反応ダイナミクスを
時間分解過渡吸収測定により研究した。
(1) 10 mJ/cm2以下のNIRパルス照射下では、
光退色物質の量はパルス強度の2乗に比例した。
(2) 10 mJ/cm2以上の強度領域では、強度の増加に伴い、
光退色物質に対するロイコ体の量比は減少したが、
シス体の生成量比はほぼ一定であった。
(3) パルス強度の増加に伴い、光分解を引き起こすNIR多光子励起の光子数が.
2から4へと増加したことを示唆している。
(4) 主な光退色物質は炭素共役鎖が切断されたフラグメントである。
(5) 光ブリーチングの時間プロファイルは3つの指数減衰成分の和により再現された。
(6) 14 psの成分が多光子励起光分解反応ダイナミクスを反映していると同定した。
Acknowledgement
Special thanks to members of Molecular Photoscience Research Center
in KOBE university.
M. Fuyuki
A. Wada
Prof. Keisuke
Tominaga
Prof. Seiji
Akimoto
Prof. Hiroshi Onishi
This work was financially supported by a Grant-in-Aid for Scientific Research (B) (Grant
No. 21 350 013) from Japan Society for the Promotion of Science (JSPS).

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