Organic electronic applications and charge transport mechanism in novel discotic liquid crystals

Abstract

ABSTRACTTriphenylene-based pentaalkynylbenzene dyads and naphthophenanthridine derivativediscotic mesogens have been proven a backbone-like utility for modern optoelectronic applications. Herein, we present the charge transport and organic electronic applications of naphthophenanthridine derivatives and a dimer composed of pentaalkynylbenzene (PA) and triphenylene (TP) discotic liquid crystals (DLCs). Naphthophenanthridine derivatives exhibit a hexagonal columnar (Colh) phase; whereas, triphenylene-pentaalkynylbenzene dyads show a columnar centred rectangular (Colr) phase and transform into Colh phase on doping the pure compounds with an electron-acceptor 2,4,7-trinitrofluorenone (TNF) in a 2:1 TNF/compound ratio. The ambipolar charge transport behaviour of the compounds mentioned above has been investigated by the time-of-flight technique. Naphthophenanthridine derivative renders an ambipolar charge transport, showing temperature-independent electron and hole mobility of the order of 3 × 10−4 cm2/Vs; whereas, TP-PA dimer yields an ambipolar charge carrier mobility of order 10−3 cm2/Vs. The phenazine-fused triphenylene DLC shows unipolar hole mobility of the order of 10−4 cm2/Vs; whereas, hydrogen-bonded Hpz-C9-TP DLCs exhibit ambipolar charge mobility of the order of 10−2 cm2/Vs. The high ambipolar charge carrier mobility in the investigated DLC compounds makes them suitable for fabricating organic semiconducting electronic devices.