Photoconduction in Charge‐Transfer Complexes

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.