Effect of π-conjugation units on the liquid crystal and photovoltaic performance of heterocyclic pyridine-based compounds

ABSTRACT

A series of new calamitic liquid crystals (LCs), 4-(5-((4-(2-(trans-4-n-alkyl- cyclohexyl)ethyl)phenyl)ethynyl)-thiophen-2-yl)pyridine comprising a cyclohexyl, a phenyl and two heterocyclic (pyridine and thiophene) ring core system, terminal alkyl chain, ethane and acetylene linkers were synthesised and characterised. Their structures were confirmed by infrared spectrometry (IR), nuclear magnetic resonance (NMR) and mass spectrometry (MS), and the LC properties were investigated through differential scanning calorimetry (DSC) and polarising optical microscopy (POM). Dye-sensitised solar cells (DSSCs) were assembled to evaluate the photovoltaic properties of these materials. Furthermore, three compounds 3 N, 3 N-1 and 3SN have successfully been utilised to study the effect of π-conjugation units on the LCs properties and photovoltaic performance. The results show that thienyl unit instead of phenyl unit benefits photovoltaic performance, while it is not favourable to the stability of the nematic mesophase and birefringence. Meanwhile, DFT calculations of molecular conformation, frontier molecular orbital and dipole moment were used to correlate the experimental findings.

Graphical abstract

KEYWORDS:

• Liquid crystals
• photovoltaic performance
• heterocyclic ring
• DFT calculations

Disclosure statement

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

Additional information

Funding

Research was supported by the National Science Foundation Committee of China [21673134], Program for Science & Technology Innovation Team of Shaanxi Province [2018TD-030], International Science and Technology Cooperation Project of Shaanxi Province [2021KW-20], and the Fundamental Research Funds for the Central Universities [GK202103054].