Photoreactions in Langmuir-Blodgett Films

Photoreactions in Langmuir-Blodgett (LB) films were studied with special attention directed to structural changes of LB films accompanied by the photoreactions. First, a counter concept of free volume is presented. Three-dimensional cone-shaped structures were developed with trans-to-cis photoisomerization in polyion complex LB film of a water-soluble amphiphilic azobenzene. The structures alternately appeared and disappeared by illumination with UV and then visible light. The concept of free volume was found not to hold in the present case. Photoinduced J-aggregate formation of non-photochromic and photochromic dyes is discussed. Reversible photoisomerization of azobenzene in mixed LB films of azobenzene and dyes triggered irreversible J-aggregate dye formation. J-aggregate formation was accompanied by irreversible large morphological changes of the films. The photoisomerization of azobenzene served to induce self-organization of dye molecules. The photopolymerization of amphiphilic diacetylenes was investigated in LB films. This process was found to consist of blue-red, red, and yellow phases based on the spectral change. This change was found to depend on molecular orientation in the LB films. During the blue-to-red transition, the LB films showed considerable morphological change.