Acid‐Responsive Absorption and Emission of 5‐N‐Arylaminothiazoles: Emission of White Light from a Single Fluorescent Dye and a Lewis Acid

Solutions of 5‐N‐arylaminothiazoles containing pyridyl groups exhibited clear halochromism and halofluorism upon addition of Brønsted and Lewis acids. The addition of triflic acid to solutions of 5‐N‐arylaminothiazoles in Et(2)O induced bathochromic shifts of the absorption and emission bands. DFT calculations suggested that the spectral changes arise from the protonation of the pyridyl group of the thiazoles in Et(2)O. Single‐crystal X‐ray diffraction analysis of a thiazole and its protonated form revealed the change of the conformation around the thiazole ring. The emission of white light was accomplished from a single fluorescent dye by adjusting the ratio of dye and B(C(6)F(5))(3), whereby the International Commission on Illumination coordinates showed a linear change from blue to orange.