Photoemission from Polycyclic Aromatic Crystals in the Vacuum Ultraviolet Region. III. Aromatic Crystals and Charge-transfer Complexes

Abstract

The photoemission from various types of charge-transfer complexes, quinolinium-tetra-cyanoquinodimethane Q(TCNQ₂ (I), dibenzophenothiazine (DBP)-dicyanodichloro-p-benzoquinone (DDQ)[(DBP)(DDQ)(II) and (DBP)₂(DDQ)(III)], trinitrobenzene (TNB)-coronene (IV), and TNB-perylene (V),and also large polycyclic aromatic hydrocarbons, violanthrene A (VI), violanthrene B (VII), coronene (VIII), pyranthrene (IX), and pyranthrone (X), was observed in the vacuum ultraviolet region. The experimental equation Y ∝(E–E^*)³, where Y is the quantum yield of photoemission; E, the incident photon energy, and E^*, the threshold energy, was used to determine the ionization potential. The E^*-values, as estimated from the experimental equation, were I=4.85 eV, II 4.99, III 4.75, IV 5.62, V 5.52, VI 5.06, VII 5.13, VIII 5.58, IX 5.04, and X=5.71 eV. A band structure scheme for these organic semiconductors was introduced to analyse the emission mechanism.