The relation between colour and structural changes in thermochromic systems comprising crystal violet lactone, bisphenol A, and tetradecanol

Abstract

The aim of the paper was to find a direct connection between dynamic colour changes, phase changes and chemical interactions in model three-component leuco dye based thermochromic systems. The model systems, containing crystal violet lactone as a colour former, bisphenol A as a developer and 1-tetradecanol as a co-solvent, were analysed by DSC and FTIR spectroscopy and the results were related to the characteristics of the dynamic colour change. The ternary thermochromic systems were also compared with binary mixtures of the co-solvent with the developer and colour former, respectively. The temperatures characterizing the dynamic colour change at decolouration limits were directly related to the solid–liquid transition on heating and liquid–solid transition on cooling, regardless the concentration of bisphenol A. In ternary thermochromic systems, an indistinctive phase transition at the temperatures below the solid–solid (crystal–rotator) transition was observed. The straight connection between the phase transitions and temperatures characterizing the dynamic colour change at colouration limits was not proved. The colour contrast of thermochromic systems was found to be directly related to the ratio of integrated intensity of lactone ring opened (solid) and lactone ring closed (liquid) carbonyl vibration characterized by infrared spectroscopy.