Evidence for Temperature-Dependent Electron Band Dispersion in Pentacene

Evidence for temperature-dependent electron band dispersion in a pentacene thin film polymorph on graphite is provided by angle- and energy-dependent ultraviolet photoelectron spectroscopy. The bands derived from the highest occupied molecular orbital exhibit dispersion of $\sim 190\mathrm{meV}$ at room temperature, and $\sim 240\mathrm{meV}$ at 120 K. Intermolecular electronic coupling in pentacene thin films is thus confirmed to be dependent on temperature and possibly crystal structure, as suggested by additional infrared absorption measurements.