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
ICG (indocyanine green)
Cyanine dye
! Geometric structure ! Electronic structure
Photosensitive pigment
Intensive studies for a century
S1←S0
Low quantum yield of photoreaction from S1: ~10-5[Gratz et al. (1999)]
photodetector for specific cancers [Sugie et al. (2010)]
500 600 700 800 9000
1
2
3
4
Absorb
ance
Wavelength / nm
Multiphoton reactions under fs irradiation
500 600 700 800 900-0.9
-0.6
-0.3
0.0
A
Wavelength / nm
N
SO3Na
CH3CH3
CH3
CH3
N+
SO3Na
N
SO3Na
CH3
CH3
N+
SO3Na
CH3
CH3
cis-isomer
leuco-form
saturation of
C=C bonds [Holzer et al. (1998)]
Transient absorption
Pump pulse: 800 nm, 70 fs, 40 mJ/cm2
Pump-probe delay: 2.5 ns
[M. Fuyuki et al. (2013(1))]
pump
1 101E-5
1E-4
1E-3
0.01
0.1
(890 nm)
(560 nm)
2.9
3.9
cis-isomer
leuco-form
60
slope =
slope =
A
NIR fluence / mJ / cm2
NIR pump fluence dependence
cis-
isomer
(new)
leuco-
form
(new)
conve
ntional [9]
conve
ntional[9] one-photon process:
buried in multiphoton process
ioni
-zation
Quantum yield: higher electronic state >> S1
[M. Fuyuki et al. (2013(1))]
Today’s topic: Reaction dynamics of photodegradation
Experimental setup（transient absorption）
Cyanine dye in ethanol:
0.6 mM
Thickness of jet:
0.2 mm
Spot size:
pump 0.2 mm
probe 0.1 mmProbe pulse
Sample jet
probe pulse(white light continuum)
photomultiplier tube
monochoromator
sample
chopper
regenerativeamplifier pump pulse
water flow cell
delay stage
PC
Lock-in amplifier
wave plate
f=500 mm
f=250 mm
f=100 mm f=150 mm
800 nm70 fs1 mJ1 KHz
[Fuyuki et al. 2010, 2011, 2013]
(magic angle)
500 600 700 800 900
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
Probe Delay
0.0 ns
0.5 ns
1.0 ns
1.5 ns
2.0 ns
2.5 ns
A
Wavelength / nm trans isomerS0
S1
S2
0.46 ns
Transient absorption spectra
Excited state absorption (ESA) [Meyer et al. (1998)]
Photo-bleaching (PB) of trans-isomer [Philip et al. (1996)]
1 pump – 1 probe measurement
PB
ESA
NIR pump fluence = 50 mJ/cm2
[Ashworth et al. (1996) ]
1 10
3.9
3.0
2.0
photobleaching
leuco forms
cis isomers
slope =
1
10-5
10-4
10-3
10-2
10-1
50
slope=
slope =
|A
|
NIR fluence / mJ / cm2
NIR pump fluence dependence
Main photodegraded species were ICG fragments.
0 10 20 30 400.00
0.03
0.06
0.09
Ratio o
f |
A|
NIR fluence / mJ / cm2
leuco forms
vs photobleaching
cis isomers
vs photobleaching
Photoproducts vs photobleaching
Optical order of photodegradation changed from 2 to 4.
3 photon
4 photon
Steady state spectra
400 500 600 700 800 900
0
1
2
3
Absorb
ance
Wavelength / nm
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)
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) ]
0 500 1000 1500 2000
0.0
0.3
0.6
0.9
1.2
-A
(785 n
m)
Pump-probe delay / ps
Experiment
Model
decay 1 (485 ps)
decay 2 (14 ps)
decay 3 (1.4 ps)
Temporal profile of photobleaching
0 10 20 30 40 50
0.0
0.3
0.6
0.9
1.2
-A
(785 n
m)
Pump-probe delay / ps
Experiment
Model
decay 1 (485 ps)
decay 2 (14 ps)
decay 3 (1.4 ps)
The profile includes 3 exponential decay components.
Assignment
14ps time constant corresponds to photofragmentation.
Decay components 1 and 3 correspond to
relaxations in trans singlet system.
Assignment
14ps time constant corresponds to photofragmentation.
Decay components 1 and 3 correspond to
relaxations in trans singlet system.
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。
Conclusions
A. Wada
AcknowledgementSpecial thanks to members of Molecular Photoscience Research Center
in KOBE university.
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).
Prof. Keisuke
Tominaga
Prof. Hiroshi Onishi
Prof. Seiji
Akimoto
M. Fuyuki
