Solution processable ter-anthrylene-ethynylenes semiconductors: thin film transistor properties and STM study on HOPG and Au(111)

The article reports the properties of new solution processable 9,10-ter-anthrylene-ethynylenes functionalised with n-butyl (B3A) n-octyl (O3A) and 2-ethyl-hexyl (E3A) functional groups. The characterization of the oligomers as organic semiconductors in solution processed top-contact bottom-gate OTFT devices reveal that E3A shows the best figures of merit (average μ of 1.1 ± 0.1 × 10⁻² cm² V⁻¹ s⁻¹ and on/off ratios of 10⁵). Spontaneous physisorption of all the molecules on both highly ordered pyrolytic graphite (HOPG) and reconstructed Au(111) surfaces allowed the study of their self assembling behaviour at the liquid–solid interface by scanning tunnelling microscopy. STM revealed a peculiar behaviour for B3A, bearing shorter n-butyl chains, that arranges in a quasi hexagonal packing on HOPG, differently from the other molecules showing the formation of lamellae rows on this substrate. Due to the stronger interactions with the ter-anthrylene-ethynylene cores, on Au(111) surfaces, all structures self assemble in closer lamellar rows with very similar geometric parameters, independently from the alkyl chain length that are assumed to be tilted off the surface.