Photochemistry of linear and cyclic oligo- and poly(aryleneethenylene)s — applications in materials science

Abstract

Abstract A variety of alkoxy-substituted oligo- and poly(aryleneethenylene)s were prepared by applying a new synthetic approach to optimize the photoconductivity, which is strongly influenced by the number, position and length of the side-chains. Measurements of the photodischarge were performed in dispersion layers or cast films. Irradiation in the visible region leads solely to the generation of charge carriers, whereas irradiation in the UV causes primarily a transformation of the benzenoid building blocks to quinoid systems and finally a photopolymerization reaction. The same synthetic procedure can also be used for the preparation of cyclic oligomers. Some alkoxysubstituted triphenanthro[18]annulenes obtained via this route exhibit liquid crystal (LC) properties. The disc-like molecules are arranged in pairs which form photosensitive nematic discotic N D phases. As for the openchained compounds, photopolymerization reactions are observed on irradiation, i.e. the LC phases sustain an irreversible photodegradation.