The charge transfer complexes of 2,2′-bithienyl, 5,5′-dimethyl-2,2′-bithienyl, and some thiophene derivatives as donors with tetracyanoethylene as an acceptor have been studied spectrophotometrically. In addition, complexes of the first donor with chloranil and iodine have been studied. The formation constants and extinction coefficients of the molecular complexes formed have been determined by graphical as well as iterative methods. From measurements at different temperatures, the thermodynamic functions of the complex formation have been calculated. The ionization potentials of the donors have been obtained from the energies of the charge transfer transitions.

The electronic absorption spectra of 2,2′-bithienyl and a number of its derivatives have been investigated. The predominant conformer as well as the polarity of the molecule were predicted from the spectrum. Molecular orbital calculations were performed on different conformers of 5-formyl-2,2′-bithienyl and the s-trans geometry proved to be the predominant conformer of the molecule. A good agreement is observed between calculated and observed transition energy and intensity.