Optical properties of the ion‐radical salts of tetracyanquinodimethane in the solid state

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Abstract
Absorption spectra of TCNQ salts with different donors — metals, organic conjugated compounds, dyes in solid state‐are investigated. The study was carried out on thin films obtained by grinding of salt on quartz substrate. For the Cs(TCNQ) salt reflection and absorption spectra were investigated on single crystals. Salt spectra in the solid state differ greatly from the isolated anion‐radical spectrum. For simple salts there is a close resemblance between thin film spectra and the spectrum of the () dimer, which proves that in the solid state pair interaction of ion‐radicals predominates. Complex salt spectra are characterized by strongly smeared absorption bands, especially in the Qn+ (TCNQ) salt. The correlation between absorption spectra and electrical and magnetic properties of the salts is noted. For Cs(TCNQ) single crystals a stronganisotropy of reflection and absorption is found. Both intensity and character of the absorption spectra depend on the polarization direction. The obtained data are correlated with the strong intermolecular interaction along TCNQ molecule stacking directions and the translational symmetry of the crystal. Absorption spectrum changes during destruction of the crystalline structure are found. The absorption spectra of TCNQ derivatives of dyes in solution are the result of superposition of ion‐radical bands and the initial dye band. The character of the solid film spectrum is connected with the influence of the steric factor on the intermolecular interaction.