Polarized Absorption Spectra of Crystals of Indole and Its Related Compounds

Abstract The polarized absorption spectra of crystals of indole derivatives have been measured in order to confirm the presence of two types of electronic transitions, 1Lb and 1La, in the long-wavelength absorption region, and in order to determine the direction of their transition moments. The polarization spectra show that the 1A–1Lb electronic transition forms a sharp absroption band with vibrational structures lying below a broader absorption band of the 1A—1La transition. The transition memont direction of the 1Lb makes an angle of 54° to the long axis of the molecule, while that of the 1La lies at an angle of −38° to the same axis. These results were compared with the results of theoretical calculations of the P–P–P SCF MO–CI method.