Interaction of multiporphyrin systems with molecular oxygen in liquid solutions: extra-ligation and screening effects

Steady-state and time-resolved studies indicate that for a sequence of porphyrin or chlorin chemical dimers Zn-cyclodimer→(ZnOEP) 2Ph→(ZnOEP) 2→(ZnHTPP) 2→(ZnOEChl) 2 with relative lowering of excited S 1- and T 1-states, the extra-ligation by pyridine (PYR) does not influence essentially on fluores...

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Bibliographic Details
Published in:	Chemical physics Vol. 275; no. 1; pp. 211 - 230
Main Authors:	Sagun, Eugenii I., Zenkevich, Eduard I., Knyukshto, Valentin N., Shulga, Alexander M., Starukhin, Dzmitry A., von Borczyskowski, Christian
Format:	Journal Article
Language:	English
Published:	Elsevier B.V 2002
Subjects:	Excited states quenching by molecular oxygen Extra-ligation Pentads Porphyrin and chlorin dimers Screening Triads Screening Extra-ligation Excited states quenching by molecular oxygen Triads Pentads Porphyrin and chlorin dimers
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Summary:	Steady-state and time-resolved studies indicate that for a sequence of porphyrin or chlorin chemical dimers Zn-cyclodimer→(ZnOEP) 2Ph→(ZnOEP) 2→(ZnHTPP) 2→(ZnOEChl) 2 with relative lowering of excited S 1- and T 1-states, the extra-ligation by pyridine (PYR) does not influence essentially on fluorescence parameters but leads to an increase of T 1-states non-radiative decay (the most pronounced for dimers with higher lying T 1-levels). For pyridinated dimers at 293 K T 1-states quenching by molecular oxygen depends on the spacer flexibility and donor–acceptor interactions with PYR. In self-assembled triads and pentads energy and electron transfer (within a few ps) takes place from Zn-dimers to pyridyl substituted porphyrin extra-ligand, H 2P, followed by the effective population of H 2P T 1-state. For these systems, bimolecular constants of H 2P T 1-states quenching by O 2 decrease by 1.4–1.8 times with respect to those found for individual monomeric porphyrins. This effect is explained by the screening action of a strongly quenched Zn–porphyrin dimer subunit limiting the access of oxygen molecule to the excited extra-ligand.
ISSN:	0301-0104
DOI:	10.1016/S0301-0104(01)00517-1