STM and DFT examination of self-assembled 5,6,7-trithiapentacene-13-one on vicinal gold (788)*

The novel pentacene derivative 5,6,7-trithiapentacene-13-one (TTPO) is a robust electron donor candidate for use in high temperature photovoltaic devices. STM imaging has revealed interesting nanoscale surface structures of TTPO molecular chains as well as an ordered self-assembled monolayer on 3.9nm wide gold (788) surface terraces. TTPO is a polar species of pentacene with centered oxygen and sulfur bridge substituents. It is along this sulfur bridge that TTPO arranges itself laterally with a small cant angle between the molecule and the gold surface. This lateral assembly varies from the common flat-lying and standing-up phases of pentacene on surfaces. Combining imaging with density functional theory calculations allows for classification of these self-assembled structures with particular interest being directed toward the interaction between TTPO and gold at this organic-metallic interface. Understanding the structure of organic-metal interfaces with molecular precision potentially allows for the tailoring of those interfaces in order to maximize charge carrier transport.