Structural and optical properties of 6,13-pentacenequinone thin films

We report on the structural and optical properties of 6,13-pentacenequinone thin films deposited on n -Si substrates by thermal evaporation at room temperature. X-ray diffraction data indicate excellent crystallinity but the films have two crystalline phases mixed. Photoluminescence (PL) spectra exhibited double peaks at 1.97 and 2.09 eV while the corresponding (double) peaks, associated with the highest occupied molecular orbital-lowest unoccupied molecular orbital transition, were also observed from direct absorption spectra at 2.94 and 3.11 eV. The yellow PL band was quite intense under UV illumination; the intensity was comparable to that from Tris-(8-hydroxyquinoline) aluminum ( Al q 3 ) thin films. A large Stokes shift of ∼ 1 eV found in our 6,13-pentacenequinone thin films suggests potential applications to UV-detectors and UV-detecting cards.