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- Title
Comparative analysis of the influence of bulky β-alkyl substituents on fluorescent properties of some series of spatially distorted <i>meso</i>-phenyl substituted porphyrins.
- Authors
Sagun, E. I.; Zenkevich, E. I.
- Abstract
We present results of our systematic investigation and comparative analysis of the spectral-kinetic properties of absorption and fluorescence of two series of related planar porphyrins in liquid media at 293 K, in which deviations from the planarity are caused by contact steric interactions of eight peripheral β-pyrrole methyl (−CH 3) or ethyl (−C 2H 5) groups with a successively increasing number (from one to four) and varying position of meso-phenyl (Ph) substituents in the porphyrin macrocycle. It is substantiated that considerable differences between the spectral-kinetic properties of absorption and fluorescence of the octaethyl- and octamethylporphyrin molecules, which have the same number of meso-phenyl substituents, are caused by fundamentally different roles played by β-ethyl and β-methyl groups, which differ in volume and which determine differences in the character of steric interactions and the efficiency of the dynamic relaxation of the tetrapyrrole macrocycle. It is revealed that there is a difference between calculated ftheor and experimentally determined fexp values of the fluorescence probability, which is caused by conformational rearrangements of spatially distorted porphyrin macrocycles in the S1 excited state, which reduce the oscillator strength and lower the energy of the long-wavelength transition S0 → S1. It is found that the chemical nature, the size, and the number of bulky -CH 3 or -C 2H 5 β-pyrrole groups affect weakly rate constants of fluorescence quenching by molecular oxygen and do not create noticeable steric hindrances for contact interactions of the oxygen molecule with the π-conjugated system of the tetrapyrrole macrocycle.
- Subjects
ALKYL compounds; COMPARATIVE studies; SUBSTITUENTS (Chemistry); PHENYL compounds; PORPHYRINS; ABSORPTION spectra; FLUORESCENCE spectroscopy
- Publication
Optics & Spectroscopy, 2013, Vol 115, Issue 5, p727
- ISSN
0030-400X
- Publication type
Article
- DOI
10.1134/S0030400X13110210