Polarized Absorption Spectra of Single Crystals of Ion Radical Salts. I. Molecular Compounds of 7,7,8,8-Tetracyano-p-quinodimethane with N,N,N′,N′-Tetramethyl-p-phenylenediamine and N,N-Dimethyl-p-phenylenediamine

Abstract

Abstract Polarized absorption spectra in the 10–40 kK region were observed on single crystals of the molecular compounds of tetracyano-p-quinodimethane(TCNQ) with tetramethyl-p-phenylenediamine (TMPD) and with dimethyl-p-phenylenediamine (DMPD). These molecular compounds possess an ionic structure in the ground state. A strong, broad absorption band appears in the near-infrared region of the crystal spectra with a polarization parallel to the crystal axis along which the component ions are alternately stacked making their molecular planes parallel to each other. The absorption maximum of this band is located at 7.7 kK in TMPD·TCNQ and at 8.5 kK in DMPD·TCNQ. These bands are assigned as a one associated with the charge transfer from TCNQ− ion to the positive ion of the donor. Other absorption bands found in the spectra can be assigned as local excitation bands associated with the intramolecular transitions of the component ions. However, they are found to be considerably broadened and appreciably shifted to higher energy as compared with the solution spectrum of each component ion.