In search of the thermo/halochromism of the ET(30) pyridinium-N-phenolate betaine dye

The thermohalochromic behavior of Reichardt’s ET(30) betaine – the temperature-dependent variation of its halochromic band in the presence of a cation – was investigated for the first time in NaI solutions of HBD- (methanol, ethanol, 1-propanol, 1-butanol) and non-HBD-solvents (acetonitrile, dimethylformamide) at 15 and 55 °C. The solvent-dependent thermohalochromism of the pyridinium-N-phenolate betaine dye was interpreted in terms of the effect of the temperature on the dye–cation association in solution.

Figure optionsDownload as PowerPoint slideHighlights
► The halochromism of the ET(30) dye is affected by temperature in what is termed thermohalochromism.
► The phenomenon was studied for the first time in NaI solutions of the ET(30) dye in HBD- and non-HBD-solvents.
► A rise in temperature may increase or decrease halochromic shifts, leading to a positive or negative thermohalochromism.
► The effect depends on the solvent, reflecting salt–dye, solvent–salt and dye–solvent interactions.