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。生物膜的奇妙特性之一是在极薄的膜（厚度约10纳米）上存在不对称表面。在本研究中，通过在水面浇铸有机聚合物溶液制备了极薄（25-60 nm）的聚合物膜，并发现了以下新的光化学性质。(1)非对称表面的二次谐波产生（SHG）：在薄膜表面和石英衬底上成功地应用了供体-受体相互作用。两亲性卟啉和暴力素在这方面是有用的。表面吸附分子的动力学行为被SHG研究阐明。(2)光化学电子跨有机薄膜传输：将含有供体-受体对的单层薄膜固定在电极表面产生光电流。金属卟啉或钌-三联吡啶配合物均可作为供体，而紫紫素是很好的受体。在三乙基乙醇胺存在的水溶液中，观察了金或ITO电极上的阳极光电流。(3)超薄聚合物薄膜的光声响应：将超薄聚合物薄膜浸渍在有机染料中，用氙灯的切碎单色光照射在无衬底的聚合物薄膜上。用卟啉或偶氮化合物作为染料。单片薄膜就足以探测到光声信号。对于给定厚度的超蛋白聚合物薄膜，相对灵敏度明显超过相同聚合物的自旋涂覆薄膜。

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.