Ni-Bisdipyrrin Metalloligand as Potential Sensitizer in MOFs : Synthesis and Photoelectrochemical Characterization

A Ni-based 2,2’-bisdipyrrin molecule bearing peripheral benzoic acid groups (NibisdpmCOOH) have been synthesized and characterized. Electrochemical tests evidence a high LUMO energy on the molecule that, combined with its absorption properties extending up to the NIR region, may allow sensitization of thermodynamically uphill reactions, such as proton and carbon dioxide photoreduction. Therefore, a sensitized photo-anode was prepared by adsorbing Ni-bisdpmCOOH onto a TiO2 film, which showed an incident photon to current efficiency, measured at 0.61 V vs RHE, extending to visible light region. Thus, the photo-electronically excited Ni-bisdpmCOOH is effectively able to inject electrons into the conduction band of TiO2. Moreover, the Ni-bisdpmCOOH complex was successfully incorporated into the Zr-containing UiO-66 metal organic framework (MOF) through the one-pot mixed-ligands approach, thus obtaining a material that combines the visible light activity of Ni-bisdpmCOOH with the high chemical stability of UiO-66.