Polarized Light-Induced Anisotropy in Polymer Films Doped with Az Dyes in the Photostationary State Studied by IR Spectr
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Dyes in the Photostationary State Studied by IR Spectroscopy K. TAWA*, K. KAMADA**, T. SAKAGUCHI**, and K. OHTA** * Fields and Reactions, PRESTO, JST and Osaka National Research Institute, 1-8-31 Midorigaoka, Ikeda, Osaka 563, JAPAN, [email protected] * * Osaka National Research Institute, 1-8-31 Midorigaoka, Ikeda, Osaka 563, JAPAN
ABSTRACT The anisotropy induced in a series of methacrylate polymers doped with Disperse Orange 3 (D03, N0 2-phenyl-N=N-phenyl-NH2 ) was investigated by polarized FTIR spectroscopy. Three kinds of methacrylate polymers with different glass transition temperature (Tg), poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(butyl methacrylate) (PBMA), were used as polymer matrices. Observed infrared absorption bands of D03 in the polymer films were assigned to symmetric (NOs) and antisymmetric (NO2as) stretching modes of NO 2, and the C-N stretching mode of C-NH2 (C-N). The infrared dichroism was observed in these bands under the irradiation. The orientation factors, Kz, (f=x, y, z, n=trans,cis), for both isomers of D03 were determined in the photostationary stite for every polymer matrix. The factors indicate that it is difficult for NO 2 group to move in the PMMA during trans-cis-trans isomerization and that it is difficult for NH 2 group to move in the PBMA. The dynamical behavior of D03 molecules which depends on the kind of polymers could be interpreted from orientation factors. This study shows that polarized FTIR spectroscopy is one of the most powerful methods available to analyze the physical mechanisms of photoinduced anisotropy.
INTRODUCTION A polarized light-induced anisotropy [1, 2] has been previously observed in polymer films doped with photoresponsive molecules. In the polymer system containing photoresponsive molecules, the response behavior of the anisotropy can be controlled by the kind of combination between polymer and photoresponsive molecule. Recently, new techniques of optical switching [3] and holography [4] utilizing the polarized light-induced anisotropy in polymer films have been also studied. Todorov et al. [5, 6] studied photoinduced anisotropy in polymer films doped with azo dyes for transient polarization holography which can be utilized as a real-time recording. However, the physical mechanisms of photoinduced anisotropy, has not been clarified yet. In order to clarify the mechanisms, it is necessary to study the molecular dynamics under the polarized light irradiation. In this study, the photoinduced anisotropy of azo dyes in the polymer films was investigated by using polarized FTIR spectroscopy. Azo dyes have two spatial forms, trans and cis isomers. The isomerization from the trans to cis form is induced by irradiation. However, due to the instability of the cis form, it can isomerize back to the trans form thermally. When the irradiation to azo dyes is continued, azo dyes take the photostationary state where the change of absorbance is not observed. In the polymer films doped with azo dyes, the isomerization rates and the photo
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