A STUDY ON PHOTOCONVERSION BY THE USE OF ULTRATHIN ORGANIC FILMS WITH ASYMMETRIC SURFACES

以光合作用和视觉为代表的光生物过程是在生物膜中进行的。生物膜的一个奇特特性是在超薄的膜(厚度约10 nm)上存在不对称的表面。本研究通过在水面上浇注有机聚合物溶液制备了超薄(25-60 nm)的聚合物膜，发现了以下新的光化学性质。(1)非对称表面的二次谐波：利用施主-受主相互作用成功地在薄膜表面和石英衬底上实现了二次谐波的产生。两亲性的卟啉和紫精对此很有用。表面吸附分子的动力学行为通过倍频研究得到了阐明。(2)有机薄膜间的光化学电子传输：将含有施主-受体对的单层膜固定在电极表面产生光电流。金属卟啉和Ru-三联吡啶络合物是很好的供体，紫精是很好的受体。在三乙醇胺存在下，金电极或ITO电极上观察到阳极光电流。(3)聚合物超薄薄膜的光声响应：用有机染料浸渍聚合物超薄薄膜，用氙灯发出的短波单色光照射无衬底聚合物薄膜。使用了卟啉或偶氮化合物作为染料。一张胶片就足以探测到光声信号。对于给定厚度的超高聚物薄膜，其相对灵敏度明显超过相同聚合物的旋涂薄膜。

Photobiological processes, as represented by photosynthesis and vision, proceed in biological membranes. One of the marvelous properties of the biological membranes is the presence of asymmetric surfaces on extremely thin membranes (ca 10 nm in thickness).In the present study, extremely thin (25-60 nm) polymer membranes have been prepared by casting organic polymer solutions on water surface and the following new optochemical properties were discovered. (1) Second harmonic generation (SHG) at the asymmetric surface : Donor-acceptor interactions were successfully used for SHG at the thin membrane surfaces and also on quartz substrates. Amphiphilic porphyrins and viologens were useful for this purpose. Dynamic behaviors of adsorbed moleccules on the surface were elucidated by the SHG studies. (2) Photochemical electron-transport across thin organic films : Monolayr films, which contained donor-accceptor pairs, were fixed on electrode surface to generate photocurrents. Either metal porphyrin or ruthenium tris-bipyridine complex was useful as the donor, while viologen served as the excellent acceptor. Anodic photocurrents were observed on gold or ITO electrode in the pressence of triethanol amine in the aqueous solutions. (3) Photoacustic responses of ultrathin popymer films : The ultratin polymer films were impregnated with organic dyes, and chopped monochromatic light from a Xenon lamp was irradiated on the substrate-free polymer films. Either porphyrin or azo-compound was used as the dye. A single film was good enough to detect the photoacoustic signals. Relative sensitivity for a given thickness of the ultratin polymer film markedly exceeded that of spin coated film of the same polymer.