Compounds composed of [SW12−nVnO40](2+n)− and [H2TPP]2+ show significant nonlinear absorption, self-defocusing behavior and excellent optical limiting performance.

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, (, 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, 1 H NMR, ESI-MS, TG/DTA, UV−vis, fluorescence emission spectra, and cyclic voltammetry measurement. Remarkably, great enhancement in reverse saturation absorption is achieved in 1 and 2 which is ca. 1 order of magnitude greater than their individual reactants. Additionally, optical-limiting thresholds are obtained being 0.484 J/cm 2 for 1 and 0.501 J/cm 2 for 2, respectively, implying their high potential as low-power optical-limiting materials.

A family of covalently bonded hybrid compounds composed of Anderson type polyoxometalate (POM) moiety and porphyrin moiety have been synthesized and thoroughly characterized. The compounds all show remarkable nonlinear reverse saturable absorption and self-defocusing effect at 532 nm with a pulse duration τ = 6 ns, rendering them promising candidate materials for device applications in photonics and optoelectronics. More importantly, it is found that the hybrid wherein POM is coupled covalently to porphyrin through shorter bridge has an NLO response superior to the hybrid wherein POM is bonded via longer bridge to porphyrin, and the hybrid having two porphyrins connected to POM shows more enhancement than the hybrid having single porphyrin fused to POM. Disclosure of the inherent structure–property relationship is expected to be instructive for exploration of new porphyrin-POM based NLO materials. Meantime, the hybrid compounds have optical-limiting thresholds lower than 1.0 J/cm2, implying their high potential as lower power OL materials.

Two new porphyrin-polyoxometalate hybrids, namely, [(CH)N]H[{COHNC(CHO)PVWO}CNH]·CHCN 1, bearing two covalent-bonded Wells-Dawson-type polyoxometalates (POMs), and [(CH)N)]H[COHNC(CHO)PVWO{CHN}]·CHCN 2, bearing one covalent-bonded POM, have been synthesized and thoroughly characterized by means of elemental analysis, powder XRD, FT-IR, H (P, V) NMR, MALDI-TOF-MS, UV-vis spectra, and cyclic voltammetry measurement. Experimental results demonstrate that while all the compounds show remarkable third-order optical nonlinearities, the hybrids 1 and 2 are superior to their corresponding porphyrin precursors (molecular second hyperpolarizability γ = 8.0 × 10 esu for 54-N-N'(1,3-tetrahydroxy-2-(dihydroxymethyl)propan-4-diyl)benz-diamide,10,15,20-triphenyl porphyrin that is the precursor for the hybrid 1, γ = 2.6 × 10 esu for 54-N-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)benz-amide,10,15,20-triphenyl porphyrin that is the precursor for the hybrid 2), and the hybrid 1 (γ = 12.9 × 10 esu) is superior to the hybrid 2 (γ = 12.2 × 10 esu) reflecting more POM moieties covalently bonded to the porphyrin moiety exerting more significant influence on the third-order optical nonlinearities. Meanwhile, attachment of POMs on the porphyrin results in significant fluorescence quenching (fluorescence intensity is decreased 97% for the hybrid 1 and 80% for the hybrid 2 with respect to that of their corresponding porphyrin precursors) indicating strong electron transfer from porphyrin moiety to the polyoxometalate moiety. Lower transition energy, small energy difference between singlet and triplet excited states, and faster intersystem crossing (ISC) process of the hybrids are favorable to enhance the NLO responses of hybrids 1 and 2 resulting from the facile electron transfer from the porphyrin moiety to the Dawson POM moiety when the hybrids are subjected to laser irradiation, which is thought to be responsible to the superior of the hybrid 1 to hybrid 2 and the superior of the hybrids to their corresponding porphyrin precursors as well.