Structural Control of the Excited-State Dynamics of Bis(dipyrrinato)zinc Complexes:  Self-Assembling Chromophores for Light-Harvesting Architectures

The replacement of the phenyl rings at the 5,5‘-positions of a bis(dipyrrinato)zinc complex with mesityl groups transforms the molecule from a very weak emitter that deactivates rapidly after photoexcitation (Φf = 0.006; τ ≈ 90 ps) to a highly fluorescent chromophore with a long-lived singlet excited state (Φf = 0.36; τ ≈ 3 ns). The results demonstrate that steric constraints on aryl-ring internal rotation dramatically alter the excited-state properties of 5,5‘-substituted bis(dipyrrinato)metal complexes. The insights establish the foundation for tuning the photophysical properties of these chromophores for use in diverse photochemical applications.