Abstract
Abstract The triplet–triplet energy transfer between UV absorbers at room temperature has not been reported in scientific literature, although sunscreens are used at room temperature. In the present study, the bimolecular rate constants of the triplet–triplet energy transfer from a UV-A absorber, menthyl anthranilate (MA, tradename Meradimate), to typical UV-B absorbers, octocrylene (OCR, tradename Parsol 340) and octyl methoxycinnamate (OMC, tradename Parsol MCX), have been determined through the measurements of the triplet–triplet absorption of MA in solutions (acetonitrile, ethanol, and isododecane) at room temperature. These triplet–triplet energy-transfer processes are almost diffusion-controlled processes. The bimolecular rate constants of intermolecular triplet–triplet energy transfer from MA to OCR and OMC in acetonitrile were determined to be (0.9 ± 0.3) × 1010 mol−1 dm3 s−1 and (1.1 ± 0.2) × 1010 mol−1 dm3 s−1, respectively. The quenching rate constants of the triplet-state MA by OCR and OMC are comparable to that of the triplet-state MA by ground-state oxygen. There is a possibility that OCR and OMC reduce the generation of singlet oxygen by photosensitization with MA in fluid solutions. This is the first report of the direct observation of the intermolecular triplet–triplet energy transfer between UV absorbers at room temperature.
Published Version
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