Induced cholesteric solutions of highly soluble bis-salicylaldiminate Cu(II) metallomesogens and their rheological behaviour

Copper(II) complexes containing chiral centres and functionalised with citronellyl end groups were synthesised. Isomerisation of citronellyl double bond was exploited to decrease the melting temperature of the complexes and improve their solubility in organic media. The chiral metallomesogens were successfully used to produce induced cholesteric solutions in commercial nematic liquid crystals also in high concentrations. Transparent and coloured thin films were easily obtained showing good reflective properties across the visible spectrum. The rheological behaviour of the nematic and the cholesteric phases was investigated. The nematic system showed the characteristics of a tumbling phase with a very peculiar transient behaviour. The cholesteric samples also showed a very unusual, flow-history-dependent transient behaviour. The viscosity trend presumably indicates a flow-induced orientation of the cholesteric superstructure, thus opening the way to the possibility of tuning the yield stress level of the material. The results support the potentiality of these compounds for applications in light reflecting technology.