Reversible metachromasy of crystal violet on titanium dioxide: a new surface photophysical phenomenon
Crystal violet adsorbed on Degussa P-25 titanium dioxide, under certain conditions of dye loading and after evaporation of liquid solvent, exhibits a reversible color change from pink-violet to blue-violet when exposed to water vapor. The spectral changes, measured by reflectance spectroscopy, correspond to metachromasy of crystal violet that occurs in solution at different dye concentrations, due to aggregation of dye molecules. We propose a mechanism, reversible metachromasy, in which the extent of aggregation of the dye molecules in the surface water monolayers changes as water molecules adsorb or desorb. Specifically, as water adsorbs, the aggregates separate into monomers, and then as water desorbs, the molecules reaggregate.
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DOI of published version
Coon, S. R.; Zakharian, T. Y.; Littlefield, N. L.; Loheide, S. P.; Puchkova, E. J.; Freeney, R. M.; and Pak, V. N., "Reversible metachromasy of crystal violet on titanium dioxide: a new surface photophysical phenomenon" (2000). Faculty Publications. 3602.