The Charge-transfer Bands in the Crystal Spectra of Molecular Compounds of Tetramethylbenzidine and Those of Benzidine

Abstract

Abstract The polarized absorption spectra in the 280–1100 mμ region have been observed for the single crystals of eight molecular compounds which involve N,N,N′,N′-tetramethylbenzidine and benzidine as the electron donor and p-chloranil, TCNQ, 1,3,5-trinitrobenzene, and p-benzoquinone as the electron acceptor. The donor and acceptor molecules are not in the ionic states in the ground states of these molecular compounds, in spite of the low ionization potentials of tetramethylbenzidine and benzidine. The observed spectra are composed of absorption bands associated with intramolecular transitions in the constituent molecules and those associated with the charge transfer from the donor to the acceptor. It was found that the polarization of the second charge transfer band is almost perpendicular to that of the first one in the case of chloranil and TCNQ, compounds of benzidine and tetramethylbenzidine. In other cases, the first and second charge transfer bands were confirmed to be polarized nearly parallel to each other as in a usual charge transfer molecular compound.