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

ABSTRACT

Triphenylene-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 (Col_h) phase; whereas, triphenylene-pentaalkynylbenzene dyads show a columnar centred rectangular (Col_r) phase and transform into Col_h 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.

GRAPHICAL ABSTRACT

KEYWORDS:

• Discotic liquid crystal
• charge transport
• charge carrier mobility
• time-of-flight technique

Acknowledgments

DPS and AKS, respectively, are thankful to Campus France and the Research Grants Council (RGC) Hong Kong. SKP acknowledges the Science and Engineering Research Board (SERB), India for funding.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

DPS and AKS, respectively, are thankful to Campus France and the Research Grants Council (RGC) Hong Kong for financing the PHC PROCORE mobility project 46846TK (France)/F-HKUST602/20 (Hong Kong). SKP acknowledges SERB Project (CRG/2019/000901/OC).