The Polarized Absorption Spectra of Solid Molecular Compounds of Chloranil and Aromatic Amines

The polarized absorption spectra of the single crystal were observed for six molecular compounds which involve chloranil as the electron acceptor and aromatic amines as the electron donor. The molecular compounds of N,N-dimethylaniline, 1-naphthylamine, and N,N-dimethyl-2-naphthylamine have a non-ionic ground state. In these cases, the locations of the charge-transfer bands in the crystal spectra are similar to those of the corresponding bands of the 1 : 1 molecular complexes formed in the solution. The solid molecular compounds of p-phenylenediamine, N,N,N′,N′-tetramethyl-p-phenylenediamine, and diaminodurene can be regarded as ionic crystals composed of the positive ion of the donor and the negative ion of the acceptor. In these cases, the absorption bands associated with the component ions are observed in the crystal spectra, but they are broadened and appreciably shifted to a higher energy as compared with the case of the solution spectra of the ions. The absorption band associated with the charge transfer between ions is observed in the near-infrared region of the crystal spectra of these molecular compounds.