PHOTOCHEMISTRY OF LINEAR AND CYCLIC OLIGO(ARYLENEETHENYLENE)S AND POLY(ARYLENEETHENYLENE)S - APPLICATIONS IN MATERIALS SCIENCE

A variety of alkoxy-substituted oligo- and poly(aryleneethenylene)s we re prepared by applying a new synthetic approach to optimize the photo conductivity, which is strongly influenced by the number, position and length of the side-chains. Measurements of the photodischarge were pe rformed in dispersion layers or cast films. Irradiation in the visible region leads solely to the generation of charge carriers, whereas irr adiation in the UV causes primarily a transformation of the benzenoid building blocks to quinoid systems and finally a photopolymerization r eaction. The same synthetic procedure can also be used for the prepara tion of cyclic oligomers. Some alkoxy-substituted triphenanthro[18]ann ulenes obtained via this route exhibit liquid crystal (LC) properties. The disc-like molecules are arranged in pairs which form photosensiti ve nematic discotic N(D) phases. As for the open-chained compounds, ph otopolymerization reactions are observed on irradiation, i.e. the LC p hases sustain an irreversible photodegradation.