Effect of <i>π-</i>conjugation units on the liquid crystal and photovoltaic performance of heterocyclic pyridine-based compounds
Ran Chen, Lu Wang, Zhongwei An, Xinbing Chen, Pei Chen
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.