Barbiturates are known to have hypnotic properties and are used as active moiety on central nervous system. Depends up on the experiments conditions and functional group present on the drugs, make the drugs labile to photodecomposition. The photosensitized reaction of 2-thiobarbituric acid (2TBA) with methylene blue (MB) in alkaline medium using visible light has been studied. 2TBA exists in protonated and deprotonated form in equilibrium in alkaline medium. Photosensitized electron transfer from the deprotonated 2TBA to excited state MB takes place and the energy is transferred to 2TBA molecule which undergoes chemical reaction. The interconversion of protonated form to deprotonated form during the reaction is observed. The rate of the reaction has been calculated and the effect of pH, concentration of the sensitizer, the light intensity on the rate of the reaction has been studied. The quantum efficiency of the photo chemical reaction is calculated using potassium ferrioxalate actinometer and the effect of the concentration of the substrate on the quantum efficiency is calculated. The reaction mechanism and the excited states involved have been suggested.
2-Thiobarbituric Acid, Photosensitized reaction, Electron transfer reaction, Singlet - singlet energy transfer, Exciplex formation