Photoconduction in Charge-Transfer Complexes

Abstract

The photoconduction in the solid molecular complexes of pyrene with tetracyanoethylene, bromanil, and 1,3,5-trinitrobenzene has been observed. In each case, the intrinsic photoconduction arises with photon energy a little higher than the energy gap for the excitation to the conduction state, while its spectral region does not coincide with the charge-transfer band in the electronic spectrum. It has been suggested that in these ``weak'' charge-transfer solid complexes, the excited state associated with the charge-transfer band cannot contribute to conduction, and an energy diagram for the electronic state in these crystals has been proposed. A structure-sensitive secondary photoconduction has been observed in the spectral region around the threshold of the charge-transfer band, which is likely due to the interaction between charge-transfer excitons and imperfections in the crystal.