Polymers with pendant carbazolyl groups, 4. Photoconductive properties of some polysiloxanes with pendant carbazolyl groups

Abstract

Abstract The photoconductive properties of a series of polysiloxanes with pendant carbazolyl groups ( 1a—c ) are described. In these polymers the carbazole moieties are separated from the siloxane backbone by alkylene spacers of different length. The properties of the novel compounds are compared with the well known photoconductor poly( N ‐vinylcarbazole) and the model compound N ‐isopropylcarbazole. Effective charge carrier mobilities were measured by means of the time‐of‐flight technique. Polymer 1a exhibits the largest carrier mobility of the three polysiloxanes. The mobilities for polymers 1b and 1c are somewhat smaller and comparable to poly( N ‐vinylcarbazole). The transport of charge carriers in an amorphous material can be described as a hopping process. The activation energy for that process was calculated from the temperature dependence of the carrier mobility. The polysiloxanes 1a—c show the same activation energy of about 0,6 eV. The activation energies in poly( N ‐vinylcarbazole) and N ‐isopropylcarbazole are of the same magnitude as in the polysiloxanes. Two different models were used for evaluating the mobility data. The field dependence of the carrier mobility is best described by a modified version of Gill's model whereas no distinction between the two models could be made from the temperature dependence of the mobility.