Extra-ligation and screening effects upon interaction of photoinduced excited states of multiporphyrin arrays with molecular oxygen in solutions

Abstract

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 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 yields (ZnOEP)<SUB>2</SUB>Ph yields (ZnOEP)<SUB>2</SUB> yields (ZnOEChl)<SUB>2</SUB> with relative lowering of excited S<SUB>1</SUB>- and T<SUB>1</SUB>-states, the extra-ligation by pyridine does not influence essentially on fluorescence parameters but leads to an increase of T<SUB>1</SUB>-states non-radiative decay. At 293 K the T<SUB>1</SUB>-state quenching by O<SUB>2</SUB> 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<SUB>2</SUB> interaction with the second subunit. As a result, the T<SUB>1</SUB>-state quenching by O<SUB>2</SUB> in triads and pentads is decreased by 50 divided by 70 percent with respect to that for the corresponding individual monomers.