EXTRA-LIGATION AND SCREENING EFFECTS UPON INTERACTION OF PHOTOINDUCED EXCITED STATES OF MULTIPORPHYRIN ARRAYS WITH MOLECULAR OXYGEN IN SOLUTIONS

摘要

In this work we present the results showing how the extra-ligation, spacer properties and porphyrin macrocycle screening may influence on the conformational dynamics and photophysical properties of multiporphyrin arrays (chemical dimers, self-assembled triads and pentads) as well as on their interaction with molecular oxygen in solutions at 293 K. 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 does not influence essentially on fluorescence parameters but leads to an increase of T_1-states non-radiative decay (decrease of phosphorescence lifetimes and quantum yields by ～1.5/2.5 times at 77 K). At 293 K the T_1-state quenching by O_2 for Zn-dimer-pyridine complexes depends on the nature and flexibility of the spacer between macrocycles and donor-acceptor interactions with pyridine. In triads and pentads the dimeric subunit plays the role of screen weakening O_2 interaction with the second subunit (pyridyl substituted porphyrin). As a result, the T_1-state quenching by O_2 in triads and pentads is decreased by 50/70% with respect to that for the corresponding individual monomers.