|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1990 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1989 : ¥1,500,000 (Direct Cost : ¥1,500,000)
The following results were obtained from the present research on novel photochromism based on the photoinduced electron transfer and thermal reverse reactions.
1) Synthesis of ion-pair charge-transfer complexes
4, 4'-Bipyridinium ions with symmetrical and asymmetrical substituents at 1, 1'-positions and polymers containing 4, 4'-bipyridinium ions as part of the main chain were synthesized. High bulk and chemically stable tetrakis [3,5-bis (trifluoromethyl) phenly] borate was used to form salts with 4, 4'-b-bipyridinium ions, which showed specific ion-pair charge-transfer (CT) absorption.
2) Preparation of Langmuir-Blodgett films and polymer cast films
Monolayer properties of 4, 4'-bipyridinium ions with symmetrical and asymmetrical substituents were studied in mixtures with arachidic acid. Y-type Langmuir-Blodgett (LB) films with good quality were deposited. Very thin transparent polymer films were prepared by a casting method.
3) Novel photochromism upon excitation of ion-pair charge-trans
Upon CT excitation of LB and polymer films in vacuo resulted in colour changes from pale yellow to blue due to the formation of 4, 4'-bipyridinium radical cations. The blue colour disappeared in dark reversibly with lifetimes depending on temperature and microenvironment, tau _<1/e> =4 h in LB and 72 h in polymer films at 20^ﾟC. The colour change was repeated for many times.
4) Molecular control of the orientation of 4, 4'-bipyridinium radical cations
Polarized absorption spectra were measured before and after irradiation of LB films. From polarization and incident angle dependences, it was demonstrated for the first time that the molecular orientation of 4, 4'-bipyridinium radical cations was controlled by the substituents.
5) Highly sensitive detection of colour changes by optical waveguide technique
About 150-fold increase of sensitivity was achieved by this technique using a He-Ne laser. Colour changes in ultra thin films (about 20 nm) cast on a glass optical waveguide were successfully observed.
6) Optical recording by cast films of polymeric 4, 4'-bipyridinium salts
The lifetime of blue state in polymer films were considerably longer than in LB films. It was demonstrated that the optically written state was kept without decay below 0^ﾟC and was erased at higher temperatures. Less