A combined theoretical and experimental investigation on the influence of the bromine substitution pattern on the photophysics of conjugated organic chromophores.

A large series of structurally related two-photon photosensitizers with heavy atom substitution were synthesized and evaluated through a combined spectroscopic (steady-state and time resolved), photophysical and computational study. Our aim was to identify some relevant parameters related to their excited state dynamics including photo-induced singlet oxygen generation. Although these dynamics result from the interplay of many factors, we show that the triplet excited state generation kinetics can generally be correlated with the calculated values of both the spin-orbit coupling and the energy gap between S-1 and T-1 states, which themselves mostly depend on the positioning of the heavy atoms along the pi-conjugated structure rather than their number.