Design of novel copper(I) metallomesogens with benzoylthiourea ligands having peripherally connected cyano or fluoro groups

Abstract

A new set of liquid crystals based on copper(I) complexes with a cyano or fluoro group attached at the para position of an aromatic ring in a benzoyl thiourea ligand was prepared and studied for their liquid crystalline properties. Incorporating electron-withdrawing fluoro or cyano groups into the structural matrix can enhance their thermal stability, phase transition temperatures, and optical properties. The prepared Cu(Ln)2X compounds, where X = Cl, Br, or I, and 4-(dodecyloxy)-N-((4-fluorophenyl)carbamothioyl)benzamide (L1), N-((4-cyanophenyl)carbamothioyl)-4-(dodecyloxy)benzamide (L2), N-((4-fluorophenyl)carbamothioyl)-3,4-bis(octyloxy)benzamide (L3), and N-((4-cyanophenyl)carbamothioyl)-3,4-bis(octyloxy)benzamide (L4) displayed a SmA mesophase depending on the type of the attached terminal group (F or CN), number of alkoxy chains (one or two) and the nature of the halide ion coordinated to the metal center (Cl, Br or I). The structures of the compounds were characterized by 1H and 13C NMR, ESI-MS and IR studies, and their mesomorphic properties were investigated via a combination of polarising optical microscopy (POM), differential scanning calorimetry (DSC), and powder X-ray diffraction studies. These compounds were stable throughout the temperature range of the mesophases. This study further reiterates the consequential effect of incorporating cyano or fluoro groups on the mesomorphic and the size of the halide ions of the studied compounds.