Electronic Spectra of Ultra Thin Films Prepared by LB and Self-assemble Methods --4-(4-Octadecyloxyphenyl)ethynylpyridine--

Akihiko SHIBUYA, Jun OKUBO*, Hiraku SHINOZAKI, Seigo OHNO, Miki HASEGAWA,Kenichi KUMAGAI and Toshihiko HOSHI

Department of Natural Science for General Education, Faculty of Engineering, Tokyo Denki University; Musai Gakuendai, Inzai-shi 270-1382 Japan
Department of Chemistry, College of Science and Engineering, Aoyama Gakuin University; Chitosedai, Setagaya-ku, Tokyo 157-8572 Japan

4- (4-Octadecyloxyphenyl) ethynylpyridine (ODOP) with amphiphilic property was newly synthesized. Ultra thin films of ODOP were prepared by use of the Langmuir-Blodgett (LB) and self-assembly techniques. The most suitable surface pressure was estimated to be 49.0 mN m−1 for the preparation of ODOP LB films. It was found that self-assembly monolayers of ODOP are not formed at concentrations below 3.0×10−4 mol dm−3. There may be a critical concentration for the formation of self-assembly monolayers of ODOP. The electronic structure of these thin films were investigated by use of electronic absorption, polarized electronic absorption and X-ray photoelectron spectra. It was found that the structures of the two films prepared by the LB and self-assembly methods are essentially identical. The X-ray photoelectron spectra of the LB films prepared with the various surface pressures were measured. ODOP in cyclohexane shows the first electronic band at 316.9 nm in monomolecularly dispersed systems. The first electronic band splits into two bands, an intense 306 nm band and a weak 350 nm band, upon the formation of ultra thin films. Using the concept of the exciton splitting model, the behavior of the first electronic transition of ODOP was explored, and it was found that the molecular orientations in the ultra thin films are of herring bone.

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