Measurement of the lowest unoccupied molecular orbital energies of molecular organic semiconductors

The lowest unoccupied molecular orbital (LUMO) energies of a variety of molecular organic semiconductors have been evaluated using inverse photoelectron spectroscopy (IPES) data and are compared with data determined from the optical energy gaps, electrochemical reduction potentials, and density functional theory (DFT) calculations. A linear fit to the electrochemical reduction potential (relative to an internal ferrocene reference) vs. the LUMO energy determined by IPES gives a slope and intercept of −1.19 ± 0.08 eV/V and −4.78 ± 0.17 eV, respectively, and 0.92 ± 0.04 and −0.44 ± 0.11 eV, respectively, based on the DFT calculated LUMO energies. From these fits, we estimate the LUMO and exciton binding energies of a wide range of organic semiconductors.