The Reflection Spectra of Complex Salts of the Tetracyanoquinodimethane Anion Radical

Reflection measurements of the pressed pellets of two 2 : 3 complex salts and six 1 : 2 complex salts of the tetracyanoquinodimethane (TCNQ) anion radical were carried out over the 5000–43000 cm−1 range by the use of Avery’s method. The polarized normal-incidence reflection was measured for the Ph3PCH3(TCNQ)2single crystal. The observed results were examined on the basis of the composite-system method. For 2 : 3 salts, the transition energy and the oscillator strength are interpreted by the use of the N-A-A model (N: TCNQo and A-A: TCNQ anion dimer); it is concluded that the interaction between the two components, N and A-A, is weak. In the solid-state spectra of 1 : 2 salts, the assignments were made by the use of the polarization results of the normal-incidence reflection of the Ph3PCH3(TCNQ)2 crystal. Besides the four transitions corresponding to those of 2 : 3 salts, two new CT bands with weak intensities were observed and assigned. Except for quinolinium(TCNQ)2, a spectral change correlative to the electrical conductivity was found in the 1 : 2 salts and discussed in relation to the extent of the delocalization of the negative charge of (TCNQ)2−. The spectrum of quinolinium(TCNQ)2 exhibits a remarkable intensity decrease compared with those of the other 1 : 2 salts.