Chromogenesis of a black fluoran dye: Theoretical and spectral studies

Fluoran dyes are widely used as chromogenic reagents in thermochromic and photochromic materials due to their intrinsic halochromic properties. However, theoretical and spectral reports on fluoran-based chromic materials are still rare. This paper investigates the chromogenic mechanism of a black fluoran dye 2-(2,4-Dimethylphenylamino)-3-methyl-6-diethylaminofluoran (B-15) through spectral experiments and theoretical calculations. Computational chemistry was employed to optimize the geometry of B-15 and validate a chromogenic mechanism. The proposed chromogenic structure of B-15 was further verified by infrared spectra. The chromogenic performances of B-15 by four kinds of color developers were quantitatively analyzed using spectrometric methods. The study comprehensively examines the chromogenic mechanism of fluoran dyes and provides a valuable reference for practical chromogenic systems based on fluoran dyes.