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Amphiphilic Cationic Porphyrins: Photophysical and Photochemical Properties of Their Manganese and Cobalt Complexes

Metalloporphyrins play important roles in nature, due to their special spectral, coordination and redox features. Their advantageous photoinduced properties can also be exploited in various photocatalytic procedures. Water-soluble manganese and cobalt porphyrins offer good opportunities for their use in photocatalytic cycles in which the starting metalloporphyrins are in-plane complexes with a Mn(III) or Co(III) ion placed in the ligand center. In the presence of a suitable electron donor, photoreduction of the metal center can be achieved in these systems. In the presence of a suitable electron donor, photoreduction of the metal center can be achieved in these systems. The Mn(II) and Co(II) centers thus formed, due to their bigger radius, are located out of the ligand plane, forming sitting-a-top (SAT) or out-of-plane (OOP) complexes. These reactive SAT metalloporphyrins can be oxidized with an appropriate electron acceptor in a thermal or light-driven mode, regenerating the starting photocatalyst and producing a reactive reductant and subsequently an energy storing final product. We prepared amphiphilic derivatives of cationic TMPyP2+ (H2TMPyP4+ = 5, 10, 15, 20-tetrakis(1-methyl-4-pyridinium)porphyrin) with hexyl or dodecyl groups as the substitutions for the methyl groups. Thus we could study the effect of the length of the hydrocarbon chain on the photoinduced behavior of these manganese and cobalt complexes both in homogeneous aqueous solutions and in micellar systems involving cetyltrimethylammonium surfactants. This structural change significantly affected the electronic spectra of these complexes, their photoredox reactions and their stability in catalyses.

Amphiphilic Cationic Porphyrins; Manganese and Cobalt Complexes; Photophysical and Photochemical Properties

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