OpticalIy Pumped Chemiluminescence of Indole-3-Acetic Acid

Optically pumped chemiluminescence of indole-3-acetic acid (IAA) was observed and studied. Rose Bengal (RB) was used as a photosensitizer. Long-lived chemiluminescence (CL) appeared after irradiation of the IAA/RB reaction mixture by monochromatic light at 550 nm (the maximum of RB absorption) or by visible light. The CL spectrum had a maximum at 480 nm. The kinetics of the CL decay were single exponential. Single-exponential kinetics were characterized by two experimentally measured values: initial CL intensity and exponential lifetime of the CL decay. We studied the influence of five parameters: (1) the rate of irradiation fluence, (2) the time of irradiation, (3) RIB concentration, (4) IAA concentration and (5) buffer pH on the initial CL intensity and the CL lifetime. Initial CL intensity was proportional to the rate of irradiation fluence and the concentration of RB. Saturation was observed in dependencies of initial CL intensity on the time of irradiation, the concentration of IAA and the buffer pH. The lifetime of the CL decay decreased with increasing pH and did not depend on the other four parameters. The mechanism explaining the experimental results was suggested and detailed kinetic analysis was performed to prove the proposed mechanism. Quantum yield of the CL and five rate constants that are involved in the mechanism were determined.