Photoinduced Electron Transfer Reactions of Water Soluble Porphyrins in Zeolite Environment

Abstract

Excited state interactions of zeolite adsorbed porphyrins have been investigated by steady state luminescence quenching technique with certain antioxidants such as reduced glutathione, ascorbic acid and L-cysteine. The zeolite supported porphyrins, meso-tetra (N-methyl-4-pyridyl) porphyrin (H2TMPyP 4+ ) and zinc tetra(N-methyl-4-pyridyl) porphyrin (ZnTMPyP 4+ ) was prepared and characterized by various techniques such as Diffuse Reflectance Spectra (DRS), Scanning Electron Microscope (SEM), powder X-Ray Diffraction (XRD) and BET surface area. The interaction of zeolites with porphyrins are shown to increase the lifetime of the singlet excited state of porphyrins and decays are biphasic in nature. The splitting of the emission band of porphyrins occurs in 1:1 glycerol: water solution due to the changes in the dielectric of the solvation sphere associated with porphyrin. The Stern-Volmer plots of I0/I vs quencher total concentration [Q] were linear in the whole range of [Q] used. This study revealed effective quenching for zinc porphyrin compared to free base porphyrin. The effect of quenchers and zeolite acidity has also been studied. Quenching rate constant (kq) is on the order of 10 9 M −1 s −1 . The quenching reaction obeys Rehm-Weller Equation and is shown to be due to thermodynamically favoured electron transfer from quenchers to the excited singlet state of porphyrins (reductive quenching).

A divergent one-pot thiol-Michael strategy to create β-thiophene-fused porphyrins

“…Porphyrins with extended π-conjugation have received considerable attention in recent years due to their numerous applications in diverse research areas such as catalysis, 1 optoelectronics, 2 supramolecular chemistry, 3 chemical sensors, 4 photovoltaic applications, 5 electron transfer 6 and photomedicine. 7 Fascinatingly, these tetrapyrrolic macrocycles have played pivotal roles in several biomimetic processes, 8 photodynamic therapy, 9 and dye-sensitized solar cells.…”