Corrole basicity in the excited states: Insights on structure–property relationships

Abstract

Steady-state fluorescence measurements and quantum-chemical DFT geometry optimizations are applied to extend the structure-property relationships between the free-base corrole macrocycle conformation and its basicity to the lowest excited S-1 and T-1 states. Direct basicity estimation in the lowest excited S-1 state is demonstrated by means of fluorescence quantum yield measurements. The long wavelength T1 tautomer is found to retain its basicity in the S(1 )state, whereas the short wavelength T2 tautomer shows a noticeable decrease in basicity in the S-1 state, which is related to the in-plane tilting of the pyrrole ring to be protonated. The conformational changes upon going from the ground to the lowest excited T-1 state and the influence of the meso-aryl substitution pattern on the overall degree of distortions and tilting of the pyrrole ring to be protonated are also discussed from the point of view of macrocycle basicity.