We measured occupied and unoccupied energy levels of half-fluorinated and perfluorinated rubrenes (C42F14H14, F14-RUB, and C42F28, PF-RUB) thin films prepared on a highly oriented pyrolytic graphite substrate by a combination of one- and two-photon photoemission spectroscopies. It is revealed that the energy levels near the Fermi level (EF) decrease when the fluorination degree increases, where the energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are located at EF - 1.83 eV and EF + 0.9 eV for F14-RUB and EF - 2.51 eV and EF + 0.6 eV for PF-RUB, respectively. The HOMO-LUMO gaps corresponding to the energy for the creation of free photocarriers in molecular films - known as "transport gaps"- are evaluated by 2.7 eV for F14-RUB and 3.1 eV for PF-RUB.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films