Steady-state and laser flash photolysis studies on photochemical formation of 4-tert-butyl-4′-methoxydibenzoylmethane from its derivative via the Norrish Type II reaction in solution

A photochemical formation process of avobenzone (AB; 4-tert-butyl-4′-methoxydibenzoylmethane) from 1,1-(4-tert-butybenzoyl)(4′-methoxybenzoyl)butane (PrAB) is studied by steady-state and laser flash photolysis in solution. The quantum yield of the formation via the triplet state of PrAB is determined to be 0.23 in degassed acetonitrile at 295 K. The Arrhenius plots of the decay rate of triplet PrAB show that photoelimination proceeds with an activation energy of 6.0 kcal mol−1 and the frequency factor of 4.6 × 1010 s−1.