Photoinduced intramolecular charge separation in a polymer solid below the glass transition temperature

Journal Article · Mon Aug 22 00:00:00 EDT 2005 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.2008249· OSTI ID:20723038

Benten, Hiroaki; Ohkita, Hideo; Ito, Shinzaburo; Yamamoto, Masahide; Tohda, Yasuo; Tani, Keita ^[1]

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1. Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510 (Japan)

Photoinduced intramolecular charge separation (CS) in a polar polymer glass, cyanoethylated pullulan (CN-PUL), was studied below the glass transition temperature (T{sub g}=395 K). A series of three carbazole (Cz: donor)-cyclohexane (S: spacer)-acceptor (A: acceptor) molecules (Cz-S-A) was used as intramolecular donor-acceptor dyads. The photoinduced CS rate was evaluated by the fluorescence decay measurement at temperatures from 100 to 400 K. The CS rate (k{sub CS}) increased above 200 K even far below T{sub g} where micro-Brownian motions of the whole polymer chain are frozen. Below 200 K, on the other hand, k{sub CS} showed weak dependence on temperature. The temperature dependence of k{sub CS} is discussed in terms of the dielectric relaxation time of the polymer matrix. Consequently, CS below T{sub g} was well explained by a thermally nonequilibrium electron transfer (ET) formula above 200 K and by a two-mode quantum-mechanical ET formula below 200 K. The increase in k{sub CS} above 200 K is mainly caused by a thermally activated low-frequency matrix mode originating from the side-chain relaxation of polar cyano groups. The weak temperature dependence of k{sub CS} can be explained by a nuclear-tunneling effect caused by a high-frequency matrix mode (({Dirac_h}/2{pi}){omega}{sub H}=250 cm{sup -1}) and an intramolecular vibrational mode (({Dirac_h}/2{pi}){omega}{sub Q}=1300 cm{sup -1}). The high-frequency mode of the polymer matrix was attributed to a vibrational or librational motion of polar groups in the CN-PUL glassy solid.

• OSTI ID: 20723038
• Journal Information: Journal of Chemical Physics, Vol. 123, Issue 8; Other Information: DOI: 10.1063/1.2008249; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
BROWNIAN MOVEMENT
CHARGE EXCHANGE
DIELECTRIC MATERIALS
ELECTRON TRANSFER
FLUORESCENCE
GLASS
PHOTOCHEMISTRY
POLYMERS
RELAXATION
RELAXATION TIME
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0065-0273 K
TEMPERATURE RANGE 0273-0400 K
TRANSITION TEMPERATURE
TUNNEL EFFECT