Fused H-shaped tetrathiafulvalene-oligothiophenes as charge transport materials for OFETs and OPVs

A series of hybrid tetrathiafulvalene-oligothiophene compounds has been synthesised, where the tetrathiafulvalene unit is fused at each side to an end-capped oligothiophene chain of varying length (terthiophene, quinquithiophene and septithiophene). Each hybrid structure (1-3) has been studied by cyclic voltammetry and triple EPR-UV-Vis-NIR spectroelectrochemistry in the case of the quinquithiophene compound (2). Comparison is made with the corresponding half-units, which lack the fulvalene core and contain just one oligothiophene chain. The highest hole mobility of quinquithiophene-TTF 2 was obtained from field effect transistors (8.61 × 10-3 cm 2 V-1 s-1); its surface morphology was characterised by tapping mode atomic force microscopy and a power conversion of 2.5% was achieved from a bulk heterojunction organic solar cell device using PC71BM as the acceptor. This journal is © the Partner Organisations 2014

Symmetrically Disubstituted Bithiophene Derivatives of 1,3,4-Oxadiazole, 1,3,4-Thiadiazole, and 1,2,4-Triazole – Spectroscopic, Electrochemical, and Spectroelectrochemical Properties

Electrochemical and spectroelectrochemical properties of a series of new penta-ring donor–acceptor compounds, comprising 1,3,4-oxadiazole, 1,3,4-thiadiazole, and 1,2,4-triazole central ring, symmetrically connected to substituted bithiophenes, were investigated. Aromaticity and electrophilic–nucleophilic traits of the aza-heterocyclic units, fostering inductive and resonance effects that translate to conjugation enhancement and electron (de)­localization, were found a major factor determining the key electron properties of ionization potential (IP) and electron affinity (EA) of these molecules. Replacing the alkyl thiophene substituent for an alkoxy one afforded certain control over the two parameters as well. All studied compounds were found to undergo electrochemical polymerization giving p- and n-dopable products, featuring good electrochemical reversibility of their oxidative doping process, as demonstrated by cyclic voltammetry and UV–vis–NIR, EPR spectroelectrochemistry. While electropolymerization of entities differing in the heterodiazole unit was found to conserve the EA value, the IP parameter of polymerization products was found to decrease by 0.6–0.7 eV, affording an asymmetric narrowing of the frontier energy levels gap. Aided by quantum chemical computations, the effects of structure tailoring of the investigated systems are rationalized, pointing to conscious ways of shaping the electronic properties of thiophene class polymers using synthetically convenient heterodiazole π-conjugated units