S-Heterocyclic s-Indacenodifluorene: Synthesis, Properties and Thermally Tunable Ambipolar Field-Effect Mobility.

Design of semiconducting materials with facile control of charge transport and the nature of charge carriers is essential for realizing niche applications with organic electronics. Described herein are the synthesis, crystal structure, and analysis of the electronic properties of a four-stage redox amphoteric S-heterocyclic s-indacenodifluorene 6, including the study of its ambipolar charge carrier mobility (μh and μe) in organic field-effect transistor (OFET) devices. Despite being electron-rich, our investigation revealed reversible reduction potentials for 6 in the cyclic voltammetry, which is attributed to the recovery of locally aromatic thiophene and cyclopentadienyl anion units upon electron injection for the two antiaromatic S-heterocyclic as-indacene units in accordance to the Glidewell-Lloyd rule of aromaticity. In line with this, we observed an interesting thermal tunability of the nature of charge carriers from p-type to balanced ambipolar to n-type charge transport with reasonable semiconductor mobility in all regimes of transport. This behaviour is correlated with the modification of the transport levels upon annealing of the semiconductor and possible increase in the extent of π-electron delocalization with temperature. This proof-of-concept tunability of the nature of charge transport indicates the efficacy of our molecular design.