Dibenzo[a,e]pentalene-embedded dicyanomethylene-substituted thienoquinoidals for n-channel organic semiconductors: Synthesis, properties, and device characteristics

Dibenzo[a,e]pentalene-embedded thienoquinoidals with dicyanomethylene termini were synthesized as new π-extended thienoquinoidals for n-type organic semiconductors. Single crystal X-ray analysis demonstrated that the target molecule has an all trans-polyene structure with reasonable bond-length alternation in the thienoquinoidal strand, indicative of effective extension of the π-conjugation system. Thanks to their π-extended structures, not just the low-lying LUMO energy levels (-4.2 to -4.3 eV) but also relatively high HOMO energy levels (∼-5.6 eV) were characterized by means of cyclic voltammetry. Interestingly, depending on the position of the solubilizing long alkyl groups, they formed H- or J-aggregate-like structures in the thin-film state testified by the thin film absorption spectra. These distinct intermolecular interactions in the thin film state could cause different behaviours in thin-film field-effect transistors; for the former ambipolar characteristics were observed, whereas only n-type response was detected for the latter.