Photodimerization of dibenz[b,f] azepine derivatives and their reaction intermediates

Abstract

It is clearly demonstrated that the photodimerization of 5-acyl dibenz[b,f]azepine (DBA) derivatives occurs via excited triplet intermediates. The excited triplet state of 5-acyl DBA derivatives is barely formed on direct excitation, but is formed efficiently by triplet—triplet (T—T) energy transfer from a triplet sensitizer. Benzophenone-sensitized photoexcitation gave a unique reaction product, the anti-cyclobutane dimer of DBA. Under the sensitized conditions, the quantum yield for the photodimerization was estimated to be 0.15 at 25°C ([DBA]=2.0×10⁻³ mol l⁻¹). The triplet intermediate of this reaction was detected by nanosecond laser photolysis and the kinetic parameters of the triplet species were determined.