A room-temperature heptazine core discotic liquid crystal

ABSTRACT

Heptazine is the fundamental structural and functional unit of graphitic carbon nitrides and has a π-conjugated planar symmetry with semiconducting properties. Molecular self-assembly is one of the key factors to drive the electronic behaviour of π-conjugated organic molecules. To enhance the semiconductivity, heptazine is decorated at its active sites with 2,3,5-tris(dodecyloxy)aniline to get well-organised columnar packing. A novel heptazine-core room-temperature discotic liquid crystal (HDLC) with hexagonal columnar geometry is discovered. The molecular structure and mesomorphic properties of HDLC are investigated by ¹H-NMR, ¹³C-NMR, IR, polarised optical microscopy, differential scanning calorimetry and X-ray diffraction. Photophysical and electrochemical properties of HDLC are studied by UV–vis/fluorescence spectroscopy and cyclic voltammetry (CV), respectively. The energy band gap of HDLC estimated from CV at room temperature is 1.63 eV, which is much narrower than the previously reported band gap for heptazine derivatives. This decrease in the energy band can be attributed to the particular designing of HDLC for columnar packing. As a columnar liquid crystal providing a smooth path to the charge transport, HDLC with such a narrow energy band gap may find applications in organic electronics.

Graphical Abstract

KEYWORDS:

• Heptazine
• discotic liquid crystals
• hexagonal columnar phase
• optical and electrochemical properties

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the National Natural Science Foundation of China: [Grant Number 21374016]; Jiangsu Provincial Natural Science Foundation of China: [Grant Number BK20170024]; Priority Academic Program Development of Jiangsu Higher Education Institutions and the Open Research Fund of State Key Laboratory of Bioelectronics and Southeast University.