Photoelectrochemical Characterization of Thin Films of Perylenetetracarboxylic Acid Derivatives

Thin films of six N,N′-disubstituted diimide and a bisarylimidazole derivatives of 3,4,9,10-perylenetetracarboxylic acid have been sublimed on SnO₂ conductive substrates. Films grown at the substrate temperature of 160 ± 20 °C and at the rate of 0.8 ± 0.2 Å s^-1 display essentially two morphologies: (i) long interwoven crystallites with their long axes being nearly parallel to the substrate surface and (ii) a more compact structure with, in some cases, the evidence of tight-packed crystallites growing in the direction perpendicular to the substrate surface. All perylene derivatives show a dominant photoanodic behavior. The photoactive interface is always between the perylene and the redox electrolyte (hydroquinone/benzoquinone). The nonporous or porous character of the films has been established electrochemically. The results of this study have been used for the interpretation of the presence or absence of a filtering effect in the action spectra and the differences in the quantum yield for electron collection with the direction of film illumination (front side vs back side).