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

Abstract

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.

Deactivation of Excited States in Nanostructures Containing Cu-Porphyrin Subunit

“…[21,27,38,74,[77][78][79][80] The covalent stage includes the synthesis of Zn-porphyrin chemical dimers or trimers with a phenyl spacer in meso-position. The second stage presents itself the self-assembly of these dimers or trimers with meso-pyridyl substituted porphyrins (free bases or Cu-complexes) via non-covalent binding interactions (two-fold extra-ligation effect following the "key-lock" principle).…”

“…In toluene at ambient temperature, titration of the homodimer (ZnOEP) 2 Ph by tetra-meta-pyridyl containing molecules leads to the formation of pentads 2(ZnOEP) 2 Ph⊗CuР(mPyr) 4 containing two dimers bonded to the extra-ligand CuР(mPyr) 4 via non-covalent binding interactions [77][78][79][80] ( Figure 4A). Almost the same spectral position of the Soret band components and practically doubled extinction coefficients of the pentad compared to those of the triads [74] lead to the conclusion that the intense B-transitions of two dimers (ZnOEP) 2 Ph bound in the same pentad are not involved into strong coupling.…”

Molecular Interactions of Some Free Base Porphyrins with σ- and π-Acceptor Molecules

“…[45][46][47][48] Chemical properties that are known to be modified by nonplanar distortion include oxidation potentials, basicity of the inner nitrogen atoms, and axial ligand binding affinity, all of which can influence the biological function of porphyrin cofactors in proteins. A good result of nonplanar distortion of porphyrins appears in porphyrin metalation.…”

Effect of zinc substitution on molecular dynamics of protoporphyrin-IX

“…All porphyrins are intensely coloured and represent an important class of molecules that are found in nature in different forms [16][17][18][19][20]. The metalloporphyrin ring is found in many important biological systems where it represents the active site.…”