Structural impacts on the photodissociation dynamics of aromatic endoperoxides in solution

Aromatic endoperoxides dissociate in general in two steps if excited to an upper Sn (π, π∗) state. The first reaction step means breaking of one CO bond, which competes with fast internal conversion. The second step is splitting off of singlet oxygen and does not depend on solvent but on temperature. Thus thue model of a 1,6-biradical (BR) as intermediate product is favored. The decay of BR is controlled by vibrations of the bridging substituents and by resonance effects. The flow of energy alters with symmetry. These assumptions are supported by the new experimental findings in the case of anthradichromene endoperoxide.