Liquid crystal-directed assembly and phase morphology of a squaraine dye

The squaraine (SQ) dye, 2,4-bis 4-(N,N-di-n-hexylamino)-2-hydroxyphenyl]squaraine was synthesised, and a series of SQ dye/cholesteryl pelargonate binary mixtures with varying dye concentrations (1%, 3%, 7.5%, 10.8%, 15% and 20% w/w) were prepared. Their phase transitions were investigated using differential scanning calorimetry, polarised light microscopy and X-ray diffraction. The SQ dye itself exhibited no liquid crystalline behaviour. The concentration of the dye in the cholesteric compound proved to have a significant effect on the dye aggregation behaviour and phase transitions in cholesteryl pelargonate, resulting in the appearance of new mesophases and the formation of J- and H-aggregates. The texture morphology, X-ray diffraction data and UV–vis absorbance spectra provide strong evidence of the viability of liquid crystal-directed assembly of the SQ dye.