SENSITIZED AND INTRINSIC INPLANE PHOTOCURRENTS IN LANGMUIR-BLODGETT-FILMS OF 7-(2-ANTHRYL)-1-HEPTANOIC ACID

Langmuir-Blodgett (LB) films of an amphiphilic long-chain derivative o f anthracene, of which the molecular packing shows a strong resemblanc e with the ab-plane of anthracene crystals, were investigated with res pect to their photoconductive properties. Efficient photoinduced charg e carrier generation and in-plane charge transport have been observed in LB-films of (2A7), using a gap configuration. The wavelength and in tensity dependence of the quantum yield of the photocurrent in absence of a photosensitizer suggest an intrinsic bulkcharge generation mecha nism. The intensity dependence of the photocurrent suggests a combinat ion of nongeminate and alien recombination of charge carriers. The inc rease of the quantum yield in the presence of air is an indication tha t, upon photoexcitation, mobile holes are formed. By covering the mult ilayer assembly with a rhodamine containing monolayer, a significant i ncrease of the quantum yield is obtained upon excitation of both the a nthracene chromophore and the dye. In the case of dye excitation, the values and the field dependence of the photocurrents due to the photos ensitized injection of holes from the layer of excited dye molecules i nto the 2A7 multilayer resemble those obtained for anthracene crystals covered by adsorbed dyes.