Conjugated electron donor–acceptor molecules with (E)-[4,4′-biimidazolylidene]-5,5′(1H,1′H)-dione for new organic semiconductors

Abstract

New conjugated D–A molecules BTBID, BFBID, TBID, 2BIDBDT and 2BIDBT with (E)-[4,4′-biimidazolylidene]-5,5′(1H,1′H)-dione (BID) moieties are reported. Based on the respective absorption spectra and redox potentials, their HOMO (−5.30 to −5.52 eV), LUMO (−3.81 to −3.86 eV) and bandgaps (1.46–1.68 eV) were estimated. The HOMO energies and bandgaps could be effectively modulated by extending the conjugation length. The crystal structure of BTBID was presented. Intermolecular electron donor–donor interactions are present, but the intermolecular electron donor–acceptor interactions do not exist within the crystal. OFETs with thin-films of these conjugated molecules were fabricated with conventional solution-processed techniques, and p-type semiconducting properties were observed. Compared to BTBID and BFBID, thin-films of TBID, 2BIDBDT and 2BIDBT exhibit relatively high hole mobilities, reaching 0.037 cm² V⁻¹ s⁻¹, 0.022 cm² V⁻¹ s⁻¹ and 0.020 cm² V⁻¹ s⁻¹ after thermal annealing, even though the thin-films of 2BIDBDT and 2BIDBT possess poor morphologies.