Photochemical studies of 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM)

Kinetic UV-VIS absorption data following 355 and 266 nm nanosecond laser flash photolysis of 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM) solutions is presented. The kinetics of the decay of the non-chelated enol (NCE) produced following 355 nm excitation of BM-DBM solutions are analysed in terms of mixed 1st- and 2nd-order kinetics. The temperature dependences of the component rate constants are unusual and both 1st- and 2nd-order components display negative activation energies, which are explained by invoking pre-equilibria. In addition, it is shown for the first time that 266 nm laser photolysis of BM-DBM solutions leads to formation of the triplet state of the keto (K) form with a lifetime of approximately 500 ns. Under these conditions the triplet state of the K form is quenched by oxygen.