Role of central metal ions in hematoporphyrin-functionalized titania in solar energy conversion dynamics

In this study, we have investigated the efficacy of electron transfer processes in hematoporphyrin (HP) and iron hematoporphyrin ((Fe)HP) sensitized titania as potential materials for capturing and storing solar energy. Steady-state and picosecond-resolved fluorescence studies show the efficient photoinduced electron transfer processes in hematoporphyrin-TiO₂ (HP-TiO₂) and Fe(iii)-hematoporphyrin-TiO₂ (Fe(iii)HP-TiO₂) nanohybrids, which reveal the role of central metal ions in electron transfer processes. The bidentate covalent attachment of HP onto TiO₂ particulates is confirmed by FTIR, Raman scattering and X-ray photoelectron spectroscopy (XPS) studies. The iron oxidation states and the attachment of iron to porphyrin through pyrrole nitrogen atoms were investigated by cyclic voltammetry and FTIR studies, respectively. We also investigated the potential application of HP-TiO₂ and Fe(iii)HP-TiO₂ nanohybrids for the photodegradation of a model organic pollutant methylene blue (MB) in aqueous solution under wavelength dependent light irradiation. To further investigate the role of iron oxidation states in electron transfer processes, photocurrent measurements were done by using Fe(iii) and Fe(ii) ions in porphyrin. This work demonstrates the role of central metal ions in fundamental electron transfer processes in porphyrin sensitized titania and their implications for dye-sensitized device performance.