NDLI: Relaxation processes with participation of excited S $_{1}$ and T $_{1}$ states of spatially distorted meso-phenyl-substituted octamethylporphyrins

Content Provider	Springer Nature Link
Author	Sagun, E. I. Zenkevich, E. I. Knyukshto, V. N. Panarin, A. Yu. Semeikin, A. S. Lyubimova, T. V.
Copyright Year	2012
Abstract	We have performed comparative analysis of the spectral properties and photophysical parameters of spatially distorted octamethylporphyrins (OMPs) upon varying the number (from one to four) and position of bulky meso-phenyl substituents in liquid solutions at 293 K and in solid media at 77 K. It has been substantiated that, for the series of studied compounds, which are characterized by a high degree of nonplanar distortions, considerable changes in the spectral-kinetic properties of singlet and triplet states at 293 K in liquid solutions are determined by the dynamic relaxation of the tetrapyrrole macrocycle that is caused by steric interactions of meso-phenyls with neighboring bulky groups β-CH$_{3}$. The decay of T $_{1}$ states of mono- and di-meso-phenyl-substituted (trans) OMP molecules in liquid solutions has a biexponential character, which is indicative of conformational rearrangements of the macrocycle in the T $_{1}$ state. We are the first to measure the phosphorescence of spatially distorted metal-free OMP molecules in solid solutions at 77 K. It has been sub-stantiated that the decrease in the phosphorescence lifetime and quantum yield observed in the series of studied compounds with increasing number of meso-phenyl substituents at 77 K is related to a gradual increase in the probability of the nonradiative intersystem crossing, caused by the lowering of the energy of the T $_{1}$ level. We have revealed that spatially distorted tetrapyrrole macrocycles in rigid media at 77 K in the ground state are represented by two conformations. It has been found that the oxygen quenching rate constants of excited S $_{1}$ and T $_{1}$ electronic states of planar and spatially distorted porphyrin molecules are close to each other and depend weakly on the character distortion of the macrocycle. We have shown that the singlet oxygen generation quantum yield (γ$_{δ}$) of studied compounds depends on the number of meso-phenyl substituents in the OMP molecule and is determined by the character of the conformational dynamics of the tetrapyrrole macrocycle at 293 K.
Starting Page	388
Ending Page	400
Page Count	13
File Format	PDF
ISSN	0030400X
Journal	Optics and Spectroscopy
Volume Number	113
Issue Number	4
e-ISSN	15626911
Language	English
Publisher	SP MAIK Nauka/Interperiodica
Publisher Date	2012-10-25
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Optics, Optoelectronics, Plasmonics and Optical Devices
Content Type	Text
Resource Type	Article
Subject	Atomic and Molecular Physics, and Optics Electronic, Optical and Magnetic Materials

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