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

• Published in: Journal of applied spectroscopy 2023-07, Vol.90 (3), p.507-514
• Main Authors: Knyukshto, V. N., Gladkov, L. L., Maes, W., Kruk, M. M.
• Format: Article
• Language: English
• Subjects: Absorption spectra; Analytical Chemistry; Atomic energy levels; Atomic/Molecular Structure and Spectra; Corticosteroids; Density functional theory; Density functionals; Electron density; Energy gap; Fluorescence; Phosphorescence; Photoexcitation; Physics; Physics and Astronomy; Tautomers
• ISSN: 0021-9037; 1573-8647
• DOI: 10.1007/s10812-023-01560-4

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 Δ 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 Δ E ( S 1 – T 1 ) were calculated by the density functional theory method. An increase in the energy gap Δ E ( S 1 – T 1 ) was established to be due to an increase in the energy mismatch Δ 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.