Synthesis, crystal structure, tropicity and charge transport properties of diindenothienothiophene derivatives

A set of pi-conjugated diindenothienothiophene derivatives (DITTs) which formally possess an extended as-indacene core with 16 pi-electrons has been synthesised and their closed-shell configuration has been confirmed by X-ray structure analysis. Bond lengths analysis provides insight into the peculiar bond lengths observed for diindenoacene diradicaloids. The annellation mode at the outer rings has a great impact on the tropicity, optoelectrochemical properties and molecular packing. The featured molecules exhibit low energy band gap with values up to 1.30 eV and have high electron affinities with LUMO energies up to 3.86 eV. Their optical properties are similar to those of benzo-fused indeno[2,1-c]-fluorene (BIFs) counterparts possessing formally the as-indacene core. Analysis of the molecule tropicity using NICS and ACID plot shows that the central rings of DITTs are weakly antiaromatic and should be regarded as quinoidal molecules bridged by two sulphur atoms. Three out of four molecules show ambipolar behavior in OFETs with moderate mobilities.