Hysteresis of Corrole Fluorescence in Acid–Base Equilibria

The effect of sequential formation of protonated and deprotonated forms of 2,3,7,13,17,18-hexamethyl-8,12-di-n-butylcorrole in solution on their photophysical characteristics and spectral-luminescent properties was studied. The spectral characteristics of each of the two forms in the ground electronic state were found to be the same when they formed from the free base and from the antipodal form, while the fluorescence spectra of the two forms differed depending on the method of formation. Based on an analysis of spectral shifts in fluorescence spectra and fluorescence quantum yields, it was concluded that the protonated and deprotonated forms of corroles underwent specific interactions in the lower excited singlet S₁ state due to the formation of a complex solvation shell. These specific interactions were shown to lead to hysteresis of the fluorescence characteristics of the protonated and deprotonated forms of corroles with their mutual transitions caused by (cyclic) changes in the acid–base equilibrium.