ELECTRONIC-STRUCTURE OF OLIGORYLENES IN THIN SOLID FILMS

A series of oligorylenes with 2, 3, and 4 naphthalene units, symmetrically substituted by tert-butyl groups, was investigated in thin solid films by ultraviolet photoelectron spectroscopy, UV/vis absorbance, and fluorescence spectroscopy. The electronic structure of these oligorylenes was determined from these measurements and compared to theoretical and experimental data available for this class of materials. The ionization energy decreases with increasing length of the aromatic system from 5.46 to 4.59 eV, while the apparent electron affinity increases, from 2.77 to 3.01 eV. We predicted from this series the values for the polymer poly(peri-naphthalene) (PPN) and obtained an ionization energy of 3.69 eV. The fit for the predicted band gap of PPN was ca. 0.45 eV; therefore, the electron affinity should reach 3.24 eV. The polarization energy is 1.5 eV for all oligorylenes. There is a linear relation between the solid-state ionization potential and the electrochemical first oxidation potential. The slope is larger than 1, however, which may be explainable as arising from a solution solvation effect.