Cholesteric Aggregation at the Quinoidal-to-Diradical Border Enabled Stable n-Doped Conductor

Molecular Kekulé diradicals have been demonstrated to show unique optoelectronic properties as a function of their diradical character. A series of thienoquinoidal oligothiophenes from dimer to pentamer and substituted with an odd and even number of pyrrolo-dione groups have been prepared and proven to be n-dopable materials showing outstanding ambient stability and excellent electrical and thermoelectric behavior. Going from dimer to pentamer, a progressive change in the diradical character and aggregation mode is observed, with the tetramer showing an optimal diradical character that allows favorable intermolecular contacts with π−π multi-bonding features, while the presence of the two dione groups promotes a cholesteric-like π−π stacking. Both features synergistically contribute to form a material with exceptional ambient stability for an n-doped system exhibiting high electrical conductivities and thermoelectric performance.