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

Abstract

The spectral and luminescent characteristics of a solution of 10-phenyl-5,15-di(4,6-dichloropyrimidinyl)-corrole at 77 K were studied. Effective NH-tautomerization was found to occur in the lower T-1 triplet state of the long-wavelength T1-tautomer, resulting in phosphorescence being emitted only from the short-wavelength T2-tautomer. A shift of the acid-base equilibrium and deprotonation of a certain fraction of the molecules were observed at 77 K. The fluorescence and phosphorescence spectra of the deprotonated form were identified. The energy gap & UDelta;E(S-1-T-1) = 5570 cm(-1) for the deprotonated form was found to be as large as that for the free bases. The molecular conformations of NH-tautomers for a series of corroles with various peripheral substitution architectures were optimized and their electronic absorption spectra and energy gap & UDelta;E(S-1-T-1) were calculated by the density functional theory method. An increase in the energy gap & UDelta;E(S-1-T-1) was established to be due to an increase in the energy mismatch & UDelta;E(LUMO-LUMO+1). The observed trend was common for all types of studied molecular systems, i.e., both NH-tautomers of the free base and the deprotonated form. It was proposed that such a trend is an inherent property of the contracted corrole macrocycle, which has an excess of electron density as compared to the porphine system.