Photochromism in Organic Molecules

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Photochromism in Organic Molecules

• Katsuki Okuno
• Miyasaka Laboratory

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Contents

• Introduction Definition Example of
  Photochromic Molecules History
• Recent research Photochromism in single
  crystal Shape change of photochromic
  crystal Fluorescence switching by photochromic
  reaction
• Research with Lasers Observation of reaction
  dynamics Control chemical reaction by laser
• What I am going to study
• Future Prospects in Photochromism

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Definition

• Original Definition of PhotochromismPhenomenon
  that color of material is changed bylight
  irradiation. photo(light) chrom(color)
  ism(phenomenon)Similar phenomena Thermochromis
  m color is changed by changing
  temperature Electrochromism color is
  changed by gain or loss of electron Solvatochrom
  ism color is changed by changing polarity of
  solvent

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Definition

• Definition of Molecular PhotochromismReversible
  isomerization between two isomers having
  different absorption spectra, which is induced in
  at least one direction by light irradiation.

A and B have an equal molecular weight but have
different structures.
Example (diarylethene in solution)
UV light
Vis. light
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Example of Photochromic Molecules
(Hexaarylbiimidazole)
T-type
P-type
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Application and Basic Aspect of Photochromism

• Application

Quick property change
Application

• Absoption spectra
• Refractive indices
• Dielectric constants
• Redox potential
• Structure etc.

Rewritable paper Photo-memories Photo-switches Pho
to-driven actuator

• Basic

Time origin of reaction is easily determined
time-resolved detection of precise reaction
profiles
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History of Photochromism

• 1867 First discovery of photochromism
  (M. Fritsche, Comp. Rend. 1867, 69, 1035.)
• 1905 Discovery of fulgide (H.
  Stobbe, Ber. 1905, 38, 3673.)
• 1937 Discovery of azobenzene (G.
  S. Hartley, Nature 1937, 140, 281.)
• 1952 Discovery of spiropyran (E.
  Fischer, Y. Hirshberg, J. Chem. Soc. 1952, 4522.)
• 1960 Discovery of HABI (Japan)
  (T. Hayashi, K. Maeda, Bull. Chem. Soc. Jpn.
  1960, 33, 565.)
• 1967 Discovery of spirooxazine (Japan)
  (Fuji Film)
• 1988 Discovery of diarylethene (Japan)
  (M. Irie, M. Mohri, J. Org. Chem. 1988, 53,
  803.)

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Single molecular fluorescence switching by
photochromic reaction
UV light
Vis. light
fluorescent
non-fluorescent
Digital switching
T. Fukaminato, M. Irie et al., Nature, 420 (2002)
759. T. Fukaminato, M. Irie et al., J. AM. CHEM.
SOC. 126, (2004) 14843.
? Single-molecular photo-memory/switch
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Surface morphology changes of diarylethene single
crystal
Photochromic reaction occurs in crystalline phase
S. Kobatake and M. Irie, Science, 291 (2001)
1769.
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Morphology changes of diarylethene single crystal
Changing of crystalline shape is induced by
photochromic reaction
Energy of light is directly converted into
mechanical energy Photo-driven mesoscopic
actuator
S. Kobatake, M. Irie et al, Nature, 446 (2007)
778.
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Observation of Reaction Dynamics by Ultrashort
Pulsed Laser
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Mechanism of Photochromic Reaction
Excited state(S1) have limited life
time Isomerization occurs in competition with
radiative transition (fluorescence and
phosphorescence) nonradiative transition
(internal conversion and intersystem
crossing)
Measurement of reaction dynamics Revealing
reaction mechanism Determination of rate
constant Revealing the factors determining
reaction rate ? Rational principle for
development of advanced molecule
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Cycloreversion of diarylethene in PMMA matrix
excited 15-ps 532-nm laser pulse
in PMMA matrices
PS 532 nm irradiation 4.2 mJ / mm2 2 shots
5 min. 3.75 mJ / mm2 10 min. 7.5 mJ / mm2
20 min. 15 mJ / mm2
5,10,20 min.
Steady-state Xe lamp At 532 nm 0.05 mW
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15-ps 532-nm laser pulse extremely enhances
cycloreversion reaction yield
Cycloreversion reaction is more than 2500 times
enchanced by 15-ps 532-nm laser pulse excitation.
When used as optical memory Data writing ? UV
light Data reading ? weak visible light
Data deleting ? strong visible light
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Multi-photon absorption process
J. Am. Chem. Soc., 123 (2001) 753, J. Am. Chem.
Soc, 126 (2004) 14764 J. Phys. Chem. C, 111
(2007) 2730, J. Phys. Org. Chem., 20 (2007) 953,
J. Phys. Chem. C, 112 (2008) 11150. Phys. Chem.
Chem. Phys, 11 (2009) 2640, New. J. Chem. 33
(2009) 1409, Photochem. Photobiol. Sci., 9 (2010)
172.
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What I am going to study
?
Property of higher excited state
?
Role of excess vibrational energy
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What I am going to study
S1
S0
Graund state
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Future Prospects

1. Application of molecular photochromic reaction
   into control of bulk and surface properties. ex.
   hydrophilicity/hydrophobility
2. More effective and rapid response
   photo-actuatordirect change of photo-energy
   into mechanical force
3. New photochromic molecular system with nonlinear
   and threshold function.
4. Revealing the reaction dynamics intramolecular
   vibration, nonradiative transition and symmetry
   of electronic state