Polarized Absorption Spectra of Single Crystals of Ion Radical Salts. II. K(TCNQ) and Cs2(TCNQ)3

Polarized absorption spectra in the 10–40 kK region were observed on single crystals of the ion radical salts of tetracyano-p-quinodimethane (TCNQ), potassium·(TCNQ) and cesium2·(TCNQ)3. The crystal spectra are shown to be markedly different from the solution spectra of the monomer and dimer of TCNQ ion. It is shown that the 7.8 kK band of K(TCNQ) and the 11.1 kK band of Cs2(TCNQ)3 are charge-transfer bands associated with the transfer of an electron from a TCNQ− ion to the neighboring TCNQ− ion. The first-order and second-order effects were calculated on the local-excitation bands in order to explain the general feature of the observed spectra.