Direct observation of the optical anisotropy of C$_{70}$ fullerene molecules in the Shpol’skii spectra

Linear optical absorption and emission spectra of C$_{70}$ fullerene molecules in single-crystal toluene are investigated. It is established that the lines of purely electronic $S_0$–$S_1$ transitions are significantly polarized. The degree of linear polarization of the spectral lines depends on the position of the fullerene molecule in the toluene matrix and can be as high as $100\%$. The polarization characteristics of the lines can be understood in the context of a model in which the $S_0\to S_1$ electronic transition is represented by the excitation of a planar oscillator whose axis is oriented along the principal axis of the C$_{70}$ molecule. The relationship between the polarization of the spectral lines and the position of the fullerene molecule in the matrix is consistent with the conclusions drawn from a theoretical analysis of different configurations possible upon the embedding of C$_{70}$ molecules into crystalline toluene.