Polyoxometalate-Based Photoactive Hybrid: Uncover the First Crystal Structure of Covalently Linked Hexavanadate-Porphyrin Molecule

Polyoxometalates (POMs)-porphyrin hybrids can serve as multifunctional materials with fascinating photocatalytic and photovoltaic properties. However, most previous POM-porphyrin hybrids are synthesized relied on electrostatic interactions to form ion pairs, which is not stable enough and subject to leaching and poor electronic communication. To our knowledge, no specific crystalline structure of direct covalently trisfunctionalized POM-porphyrin hybrids has been identified. Herein, we discover an unprecedented polyoxometalates (POMs)-based photoresponsive cluster, {V6O13[znC(61)H(58)N(5)O(4)](2)}(2-) (denoted as V-6 - Zn-2Por), which can be synthesized by covalently grafting two tris-functionalized Zn-porphyrin ligands onto Lindqvist-type hexavanadate cluster using decavanadates (TBA)(3)[H3V10O28] (denoted as VIO, TBA = tetrabutylammonium cation) as precursor. Additionally, using tetraphenyl phosphonium as counterion, for the first time, a high-quality single crystal structure of the hybrid hexavanadateporphyrin molecule is uncovered. Interestingly, the fluorescence emission spectra show that the fluorescence intensity of the organic-inorganic hybrid is partly quenched compared to pristine porphyrins, indicating possible energy/electron transfer between POMs cluster and porphyrin under light irradiation. Their UV-vis diffuse reflectance spectra show an extended absorption in the visible-light range. Finally, the as-prepared photoresponsive hexavanadate-porphyrin molecule is proved to exhibit effective photocatalytic activity toward removal of rhodamine B (an organic dye) under visible-light illumination.