Organic Charge Transfer Salts; Absorption Spectra of Salts between the Pyrylium or Thiopyrylium Cation and the 1,1,3,3- Tetracyanopropenide or Tricyanomethanide Anion

New organic charge transfer salts composed of an organic cation (pyrylium or thiopyrylium) and an organic anion (1,1,3,3-tetracyanopropenide or tricyanomethanide) were prepared. The absorption spectra were studied both in solution and in a solid. These salts have the charge transfer band in the visible region as a result of the electronic transition from the anion to the cation. The charge transfer bands of these salts in solution are sensitive to the nature of the solvent. The charge transfer band is observed in solvents with a low polarity; this band shifts toward a shorter wavelength in solvents with a high polarity. The increase in the polarity of the solvent causes a decrease in the apparent molar extinction coefficient. The charge transfer band in the solid shifts toward a shorter wavelength compared with that in the solution. In a single crystal, the polarized absorption spectrum shows a remarkable dichroism.