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