Electronic absorption spectra of neutral perylene (C20H12), terrylene (C30H16), and quaterrylene (C40H20) and their positive and negative ions:: Ne matrix-isolation spectroscopy and time-dependent density functional theory calculations

We present an experimental and theoretical study of an interesting series of polycyclic aromatic hydrocarbons, the oligorylenes. The absorption spectra of perylene, terrylene, and quaterrylene in neutral, cationic, and anionic charge states are obtained by matrix-isolation spectroscopy in Ne. The experimental spectra are dominated by a bright state that red shifts with growing molecular size. Excitation energies and state symmetry assignments for this state are obtained by calculations using time-dependent density functional theory methods. These calculations also provide additional information and insight into the trends in oscillator strength and excitation energy for the bright states: in particular, the oscillator strength per unit mass of carbon increases along the series.