PHOTOCHEMICAL-TRANSFORMATIONS OF SULFOPHTHALEINE DYES IN THIN-FILM STATE

Photochemical transformations of phenol red, thymol blue, bromthymol b lue, bromcresol purple and bromphenol blue were studied in a thin film state by spectroscopy techniques. Sulfophthaleines in thin film state have been shown to be a mixture of three associated tautomeric forms, lactone, quinone and zwitterion, which differ in their stability in v acuum and in air, the ratio of concentrations of the tautomers being d ependent on the chemical structure of the dyes. Reactions in the dark in sulfophthaleine films led to new equilibrium tautomer concentration s, the stable forms being predominant; the dark reactions are accelera ted with an increase in temperature. Simultaneous photochromic transfo rmations (equilibrium first-order reaction) and photobleaching and pho toetching (non-equilibrium zero-order reactions) occur during photoirr adiation of sulfophthaleine films. The concentration of paramagnetic c enters (PMCs) in unexposed film is practically equal to that in powder s and substantially higher than that in UV-exposed films. A synchronou s change in concentration of the zwitterion form, in the quantity of o xygen consumed, and in the concentration of PMCs is observed in photoi rradiated sulfophthaleine layers.