Direct observation of the energy gap in lutetium bisphthalocyanine thin films

The energies of the frontier electronic states of neutral radical lutetium bisphthalocyanine (LuPc2) thin films are reported based on direct observation by a combination of ultraviolet photoemission spectroscopy (UPS) and inversion photoemission spectroscopy (IPES) techniques. Quantum chemical calculations are used to identify the states derived from the singly occupied molecular orbitals (SOMO) and singly unoccupied molecular orbitals (SUMO). The energy gap defined by the threshold onset values of the broadened SOMO and SUMO states is found to be 0.4 ± 0.1 eV.