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Steady-state and time-resolved studies indicate that for a sequence of porphyrin or chlorin chemical dimers Zncyclodimer ! ðZnOEPÞ 2 Ph ! ðZnOEPÞ 2 ! ðZnHTPPÞ 2 ! ðZnOEChlÞ 2 with relative lowering of excited S 1-and T 1states, 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 2 P, followed by the effective population of H 2 P T 1state. For these systems, bimolecular constants of H 2 P 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.

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