Electronic spectra of dithieno analogues of phenanthrene

The magnetic circular dichroism (MCD) spectra of some dithieno analogues of phenanthrene: benzo 2,1-b;3,4-b′] dithiophene (I) benzo 1,2-b;4,3-b′] dithiophene (II), benzo 1,2-c;3,4-c′] dithiophene (III) and benzo 1,2-b;3,4-b′] dithiophene (IV) are reported. For I–III the spectra corresponding to two different transition moment directions could be obtained from low-temperature linear dichroism spectra. The results compare well with theoretical energies, oscillator strengths, moment directions and MCD B-terms which were obtained from semi-empirical quantum mechanical calculations in the π-electron approximation.