Kinetics of photochemical reactions in optically dense media with reagent diffusion

The kinetics of photochemical reactions in optically dense media with reagent diffusion is considered. It is shown, by example of the photochromic isomerization A ↔ B, that if the diffusion coefficient of A differs from the diffusion coefficient of B the disturbance of the initial uniform distribution of the total photochrome concentration (A + B) along the light irradiation direction is observed. The greater the difference in diffusion coefficients, the greater the observed change in the total concentration distribution. The effect of change in total concentration along the light irradiation direction is found experimentally by the example of azobenzene dissolved in hydrogel and irradiated by UV light.