Photophysics, Photochemistry, and Photo-optical Effects in Polymer Solids

Abstract

Photophysics, photochemistry, and optical phenomena of polymers for microelectronics are closely related to one another. By using polyimides as typical examples, it is discussed how photophysics such as charge transfer process affects photochemistry such as photosensitivity of polyimides. Photochemistry such as photoisomerization induces the change in refractive indices providing the phase modulation in optical devices. Microstructure of a polymer liquid crystal is also elucidated by fluorescence spectroscopy.The interaction of light with materials is one of the fundamental subjects in natural science and technology. Phenomena related to light are called in Japanese "hikari" by using a single word, but there are one word and two prefixes concerned with light in English; "light", "photo-" and "opto-". Photochemistry and photophysics deal with the change in materials by light which usually chemists are interested in, and optics deal with the change in light by materials which has been developed mainly by physicists (i). Both aspects of the interaction between light and materials as well as their hybrid phenomena will become more and more important in the field of polymers for microelectronics and photonics. Typical examples of the materials with hybrid phenomena are photorefractive polymers where non-linear optical effects are induced by the space charge generated by the photoirradiation of photoconductive polymers (2) and a command surface where the alignment of nematic liquid crystals are controlled by photoisomerization of azobenzene layer (3). Several examples of photo-and optofunctional materials are summarized in Table I.Polyimides (PI) are well-known because of their excellent thermal stability, and they have become important as high temperature insulation materials in the microelectronics field. They are also expected to be potential materials for various thermostable microelectronics and photonics devices. In the present paper, we use polyimides as typical materials for studying photophysics, photochemistry, optical phenomena and their relations in polymer solids, and report several recent results of the charge-transfer (CT) fluorescence study of aromatic polyimides, the influence of CT state on the photochemistry of photosensitive polyimides, third-order non-linear optical properties of aromatic polyisoimides, and photochemically-induced optical effects in dye-doped polymer films. Charge-transfer and dimer fluorescence studies have also been applied to polymer liquid crystals.