Alkoxybiphenyl isothiocyanate liquid crystals: synthesis, mesomorphic properties and surface interactions

The chemically responsive properties of surface-anchored isothiocyanate-terminated (−NCS) liquid crystal compounds (LCs) have not been investigated before. Therefore, a novel series of terminal alkoxy and fluoroalkoxy tail isothiocyanate liquid crystal compounds was developed that exhibit nematic liquid crystal phase properties near ambient temperature. In order to achieve a low-melting liquid crystal compound, another series of alkoxy isothiocyanate terminal liquid crystal compounds with lateral fluorine substitution was synthesised and analysed. These lateral fluorine-substituted alkoxy isothiocyanate compounds not only lower the melting point but also show improved mesogenic behaviour compared to their non-fluorinated alkoxy isothiocyanate analogues. To investigate their potential application as chemoresponsive sensor materials, the surface anchoring behaviour of NCS-terminated LCs was investigated on metal-salt-decorated surfaces using density functional theory (DFT) calculations and experimental studies. DFT-based analysis, combined with experimental observations, revealed that mesogens bearing an isothiocyanate (−NCS) terminal group exhibit surface interactions that differ from those of mesogens with a nitrile (−CN) terminal group. We use these surface interactions to demonstrate the design of an NCS-terminated LC that responds to ozone gas.