Photochemical Reactions in Rigid Media‐i. The Effect of Gelatin on the Aerobic Photochemistry of Riboflavin in Aqueous Solution

The addition of potassium iodide to dilute aqueous solutions of riboflavin reduced both the rate of the aerobic photolysis and the fluorescence quantum yield of riboflavin in the same proportions. This indicated that under these conditions the photolysis proceeded from the singlet excited state. The addition of gelatin to aqueous solutions of riboflavin also reduced the rate of the aerobic photolysis but increased slightly the quantum yield of fluorescence. The rates and the fluorescence of solutions of riboflavin to which gelatin had been added were also reduced by the addition of potassium iodide but in this case the effect on the rate was proportionately greater than the effect on the fluorescence. The data suggests that in the presence of gelatin the mechanism of the reaction is changed and that the triplet state becomes more important.