Photoexcitation Energy Deactivation in the Solution of the 10-Phenyl-5,15-Di-(4,6-Dichloropyrimidinyl)-Corrole at 77 K

Abstract

Spectral-luminescent characteristics of the solution of 10-phenyl-5,15-di-(4,6-dichloropyrimidinyl)-corrole at 77 K have been studied. It has been found that in the lowest T₁ triplet state of the long-wavelength T1-tautomer, the effective NH-tautomerization occurs, resulting in the phosphorescence being emitted from the short-wavelength T2-tautomer only. It has been found that at 77 K the acid-base equilibrium shifted and a certain fraction of the molecules has been deprotonated. The fluorescence and phosphorescence spectra of the deprotonated form have been identified, and it has been found that the energy gap for the deprotonated form DE(S₁ - Т₁) = 5570 cm^-1 is as large as that one for the free bases. The molecular conformation of NH-tautomers for the series of corroles with different peripheral substitution architecture has been optimized by the density functional theory method, their electronic absorption spectra and the energy gap DE(S₁-T₁) have been calculated. It has been established that an increase in the energy gap DE(S₁-T₁) is due to the increase in the energy mismatch DE(LUMO-LUMO+1), and the observed trend is common for all the types of studied molecular systems: both NH-tautomers of the free base and the deprotonated form. It has been proposed that such a trend is the inherent property of the contracted corrole macrocycle, which has an excess of electron density compared to the porphine.