Carboxyphenyl Metalloporphyrins as Photosensitizer of Semiconductor Film Electrodes. A Study of the Effect of Different Central Metals

MIGUEL GERVALDO, FERNANDO FUNGO, EDGARDO N. DURANTINI, JUANA J. SILBER, LEONIDES SERENO AND LUIS OTERO

JOURNAL OF PHYSICAL CHEMISTRY B

American Chemical Society

Año: 2005 vol. 109 p. 20953 - 20962

1089-5647

Abstract               Free-base (P), Zn(II) (PZn), Cu(II) (PCu), Pd(II) (PPd), Ni(II) (PNi) and Co(II) (PCo)  5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl) porphyrins were designed and synthesized to be employed as spectral senzitizers in photoelectrochemical cells. The dyes were studied adsorbed on SnO2 nanocrystalline semiconductor and also in Langmuir-Blodgett films ITO electrodes in order to disclose the effect of molecular packing on the studied properties. Electron injection yields were obtained by fluorescence quenching analysis comparing with the dyes adsorbed on SiO2 nanocrystalline insulator. Back electron transfers kinetic were measured by using laser flash photolysis. The unmetallized and metallized molecules have different singlet state energies, fluorescence quantum yields and redox properties. The quantum yields of sensitized photocurrent generation showed to be highly dependent on the identity of the central metal. It shown that PNi and PCo do not present photoelectric effect. The other porhyrins present reproducible photocurrent being PPd the one that gives highest quantum yield even in closely packet ITO\LB films. Photocurrent quantum yields increase as the dye ground state oxidation potential becomes more anodic, which is in agreement with the observation, obtained by laser flash photolysis, that back electron transfer kinetic decrease with the increase in the driving force for the recombination process. This effect could be exploited as a design element in the development of new and better sensitizers for high efficiency solar cells involving porphyrins and related dyes.