Photokinetics of oil soluble 1,3,5-Triazine UV filters in combination with Butyl Methoxydibenzoylmethane or with Diethylamino Hydroxybenzoyl Hexyl Benzoate

Abstract

Bis-ethylhexyloxyphenol Methoxyphenyl Triazine (BEMT) was previously shown to efficiently quench the excited state of Butyl Methoxydibenzoylmethane (BMDBM) and to prevent its photodegradation. However, little is known on the consequences for the quenching molecule in this process. In this study we examined the impact of BMDBM on the photokinetics of the quencher BEMT by HPLC measurements and determination of the rate constant. We extended the investigation to Ethylhexyl Triazone (EHT) and Diethylhexyl Butamido Triazone (DBT), two 1,3,5-Triazine filters that became standardly used UVB filters in systems with BMDBM and without Octocrylene (OCR). We performed DFT computations on each studied UV filter to identify possible photostabilization mechanisms within the binary systems. Additionally, we evaluated the number of free radicals formed in formulations containing the studied mixtures. The same investigation was carried out with Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB) as an alternative UVA filter to BMDBM. Our experiments showed that EHT and DBT own no capability in photostabilizing BMDBM but confirmed the photostabilization effect of BEMT on BMDBM. At the same time, our work revealed a photodestabilization effect of BMDBM on BEMT, EHT and DBT as well as an increased UV-induced number of free radicals in the formulations containing the binary mixture of the 1,3,5-Triazine UV filters and BMDBM. This is hypothesized to be the consequence of chain reactions following the production of free radicals of destabilized BMDBM. In contrary to BMDBM, DHHB photostabilized the three 1,3,5-Triazine filters BEMT, EHT and DBT completely. Corresponding results of quantum computations predicted efficient triplet-triplet energy transfer to DHHB. No free radicals could be detected after UV exposure in the formulations containing the binary combination of BEMT, EHT, DBT with DHHB in contrast to formulations containing binary combinations with BMDBM.