INVESTIGATIONS ON THE PHOTOCONDUCTIVITY O F ALKOXY-SUBSTITUTED OLIGO(1,4-PHENYLENEETHENYLENE)S AND POLY(1,4-PHENYLENEETHENYLENE)S

The photoreactivity and the photoconductivity of the mono- and dialkox y substituted oligo- and poly(1,4-phenyleneethenylene) s 1/1'a-n were investigated in order to optimize the photoconducting properties of th ese materials. Increasing the length of the side chains enhances the a verage length of the main chain during the polycondensation and decrea ses the band gap till the limit of convergence is reached. The highest photoconductivity was observed for the 2,5-dipropyloxy system 1/1'j. Longer side chains render the charge transfer from chain to chain more difficult. The measurements were performed in dispersion layers and r elated to the industrial standard 3. Compound lm was also measured in a pure state as transparent film and compared to a poly(N-vinylcarbazo le) film which shows a dye-sensitized photoconductivity. In both cases the optimized systems 1/1' were markedly superior to the standards. T he highest sensitivity could be observed for wavelengths lambda lying close to the absorption maxima lambda(max). The compounds 1/1' have a high photostability on irradiation with visible light; however, they a re rapidly destroyed by UV light (254 nm).