Unexpected chromogenic properties of 1,3,3-trimethylspiro(indoline-2,3′-[3H]naphtho [2,1-b][1,4]oxazine) in the solid phase: photochromism, piezochromism and acidichromism

Abstract

New chromogenic properties of a spirooxazine {1,3,3-trimethylspiro(indoline-2,3 0 -[3H]naphtho[2,1-b][1,4]-oxazine), SO} are presented in this work. This molecule was found to be photochromic and piezochromic in the pure microcrystalline solid phase and also exhibited acidichromism when kept in contact with a hydrogen-donating solid phase. Photochromism was observed under continuous UV irradiation. Biexponential thermal bleaching followed the interruption of irradiation. Piezochromism was detected by applying a mechanical force to the solid powder, using either a hydraulic press or manual crushing. After discontinuing pressure, biexponential bleaching kinetics were observed. The biexponential nature of the fading processes is interpreted in terms of merocyanine (M) micro-spot formation inside the crystalline phase. The third chromogenic property of the solid spirooxazine, acidichromism, is due to the extraction of protons from an acidic solid matrix, alpha zirconium phosphate [a-Zr(HPO 4 ) 2 ÁH 2 O]. Proton transfer to SO in the solid phase causes the appearance of a purple colour. The spectral evolution is qualitatively similar to that observed in CH 3 CN solution when HClO 4 is added at room temperature and in the dark. Temporal evolution of the colour bands, in both solid and liquid phases, is interpreted in terms of an initial protonation, inducing ring-opening, and a second protonation, leading to a colourless product.

Novel Photoactive Spirooxazine Based Switch@MOF Composite Materials

“…To investigate the light induced isomerization processes and to determine the type of photochromism, UV/vis absorbance spectra before and after irradiation with UV light (λ=365 nm, 30 min) of all compounds 1 to 4 were recorded under inert conditions. Switching of pure SP−O is only possible, when deposited as thin films, in single‐crystalline phase at very low temperatures or by irradiation with intense UV light (high pressure Hg lamp) . Here, photoswitching of SP−O embedded into the different MOF frameworks was achieved by a common UV lamp at room temperature.…”

Solvent-dependent fluorescence enhancement and piezochromism of a carbazole-substituted naphthopyran

“…This finding showed that the pressure induced the cleavage of the C-O bond in pryan ring and resulted in the piezochromic reaction of solid CzNP accompanied by the change of the color. Meanwhile the absorption band was broadened and obviously red-shifted compared with that in solution caused by the compact aggregation of the ring-open isomers, due to the compression of sample [45,46].…”

Industrial organic photochromic dyes

“…be soluble in its immediate environment to give a true solution rather than a dispersion as most commercial classes do not exhibit useful photochromism as solids [21,22].…”