Abstract
Polarized optical conductivity spectra in the IR and visible range and variable-temperature photoluminescence spectra of the single crystals in the 4–300 K temperature range are reported. Density-functional theory (DFT) calculations of vibrational spectra and time-dependent DFT calculations of the excitation energies of the molecule are performed to interpret experimentally observed phenomena. Orientation of the -symmetric molecules in the single crystal is revealed by comparison of the experimental polarized IR spectra and vibrational DFT calculations. symmetry is assigned to the lowest energy singlet excited state of , and hence pure electronic excitation is found to be dipole forbidden. Fine vibronic structure found at low temperature is interpreted in terms of Herzberg-Teller and Franck-Condon mechanisms. Considerable similarity with vibronic spectra of is found and explained by presumable localization of the lowest energy electronic excitation of on the fullerenelike part of the molecule.
2 More- Received 26 August 2008
DOI:https://doi.org/10.1103/PhysRevB.79.045413
©2009 American Physical Society