Remarkable Enhancement in the Nonlinear Optical Responses of Porphyrins Realized by Combination with Polyoxometalates via Covalent Bonding: A Case Study

Integrating polyoxometalates into porphyrin moieties via covalent bond is expected to be a new approach to tune and enhance the nonlinear optical responses of porphyrins. The effectiveness and efficiency of this proposal has been examined and witnessed by studying two new hybrid compounds as a prototype, namely, (Bu₄N)₄K₂­[{C₅₂H₃₂N₅O₂Zn}­HNC­(CH₂O)₃­P₂V₃­W₁₅O₅₉]·2­(C₄H₉NO) (<b>1</b>) and (Bu₄N)₄K₂­[{C₅₂H₃₄N₅O₂}­HNC­(CH₂O)₃­P₂V₃­W₁₅O₅₉]·3­(C₄H₉NO) (<b>2</b>), in which porphyrins acting as electron donor and Dawson type polyoxometalate acting as electron acceptor are connected via short tether through covalent bond. The new compounds are systematically characterized by means of elemental analyses, FT-IR, ¹H NMR, ESI-MS, TG/DTA, UV–vis, fluorescence emission spectra, and cyclic voltammetry measurement. Remarkably, great enhancement in reverse saturation absorption is achieved in <b>1</b> and <b>2</b> which is ca. 1 order of magnitude greater than their individual reactants. Additionally, optical-limiting thresholds are obtained being 0.484 J/cm² for <b>1</b> and 0.501 J/cm² for <b>2</b>, respectively, implying their high potential as low-power optical-limiting materials