Organic Charge Transfer Salts. III. Photoconductive and Magnetic Properties of Organic Charge Transfer Salts

Abstract

Abstract The photoconductive and semiconductive properties of some organic charge-transfer (CT) salts consisting of a pyrylium or thiopyrylium cation and a polycyanoacid anion were investigated in single crystals. The salts are poor semiconductors with a resistivity of 1010–1012 ohm·cm at room temperature, but show relatively large photoconduction when irradiated with monochromatized light in the interionic CT absorption band. There is a strong possibility that the photocarrier is intrinsic in nature, being generated spontaneously from the excited CT state. A weak ESR signal observed originally in these salts increased on the CT band or near IR excitation. From the relationship between the darkcarriers, photocarriers, paramagnetic species and the excited CT state, a mechanism of electrical conduction is proposed in which the carrier generation by the CT interaction and the carrier migration by trapping conduction are involved.