Abstract
The optical absorption (OA) and photoluminescence (PL) spectra of pristine, oxygen-free films in the vicinity of the absorption edge across the highest-occupied-molecular-orbital to lowest-unoccupied-molecular-orbital (HOMO-LUMO) gap are studied to elucidate the nature of these electronic states. Structures observed in both the OA and PL spectra are identified with Herzberg-Teller vibronic coupling of the respective singlet electronic states to intramolecular vibrational modes. Similarities and differences among the PL and OA spectra of in solution, solid films, and single crystals are discussed. The larger linewidth of the film spectra is attributed to the presence of defects, presumably associated with numerous grain boundaries. Finally, the OA and PL spectra of photopolymerized solid films are presented. The features in both the OA and PL spectra are observed to broaden considerably. In addition, two of the OA bands blueshift slightly (400–800 ) and the PL features downshift by ∼330 upon polymerization. These results are consistent with the intermolecular oligomerization bond disorder and reduced symmetry of the shell imposed by the covalent bonds between molecules in the polymeric phase.
- Received 20 June 1994
DOI:https://doi.org/10.1103/PhysRevB.51.4547
©1995 American Physical Society