From Simplicity to Complexity in Grafting Dawson-Type Polyoxometalates on Porphyrin, Leading to the Formation of New Organic–Inorganic Hybrids for the Investigation of Third-Order Optical Nonlinearities

• Published in: Inorganic chemistry Vol. 58; no. 13; pp. 8763 - 8774
• Main Authors: Iqbal, Arshad, Asif, Hafiz Muhammad, Zhou, Yunshan, Zhang, Lijuan, Wang, Ting, Khurum Shehzad, Farooq, Ren, Xiaoyu
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.07.2019
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.9b01163

Four new organic–inorganic hybrids, [N­(C4H9)4]5­H­[{HNC2O­(CH2O)3­P2V3W15O59}­C44N4H29O3] (TPPOH-1POM), [N­(C4H9)4]10­H2[{HNC2O­(CH2O)3­P2V3W15O59}2­C44N4H28O2] (TPPOH-2POM trans), [N­(C4H9)4]10­H2[{HNC2O­(CH2O)3­P2V3W15O59}2­C44N4H28O2] (TPPOH-2POM cis), and [N­(C4H9)4]15­H3[{HNC2O­(CH2O)3­P2W15V3O59}3­C44N4H27O] (TPPOH-3POM), have been synthesized by covalently grafting the Dawson-type polyoxometalate (POM) [N­(C4H9)4]5­[H4P2W15V3O62] onto new porphyrins N-[1,3-dihydroxy-2-(hydroxymethyl)­propan-2-yl]-4-[10,15,20-tris­(4-hydroxyphenyl)­porphyrin-5-yl]­benzamide (TPPOH-1Tris), 4,4′-[5,15-bis­(4-hydroxyphenyl)­porphyrin-10,20-diyl]­bis­[N-[1,3-dihydroxy-2-(hydroxymethyl)­propan-2-yl]­benzamide] (TPPOH-2Tris trans), 4,4′-[10,15-bis­(4-hydroxyphenyl)­porphyrin-5,20-diyl]­bis­[N-[1,3-dihydroxy-2-(hydroxymethyl)­propan-2-yl]­benzamide] (TPPOH-2Tris cis). and 4,4′,4″-[20-(4-hydroxyphenyl)­porphyrin-5,10,15-triyl]­tris­[N-[1,3-dihydroxy-2-(hydroxymethyl)­propan-2-yl]­benzamide] (TPPOH-3Tris), respectively, in N,N-dimethylacetamide under nitrogen. The hybrid compounds were thoroughly characterized by elemental analysis, FT-IR, NMR (1H, 2D NOESY, 31P, and 51V), ESI-MS, MALDI-TOF-MS, UV–vis, and fluorescence spectroscopy. All porphyrins and their corresponding hybrids exhibited remarkable third-order nonlinear-optical responses under laser irradiation, with the intensity of light at focus E 0 being 4.2 μJ at wavelength 532 nm, pulse duration τ = 6 ns, and repetition rate 10 Hz. The molecular second hyperpolarizability (γ) values of the hybrids (TPPOH-1POM, TPPOH-2POM trans, TPPOH-2POM cis, TPPOH-3POM) were calculated to be 8.48 × 10–28 esu, 8.94 × 10–28 esu, 10.16 × 10–28 esu, and 8.93 × 10–28 esu, while the molecular second hyperpolarizability (γ) of their corresponding porphyrin precursors (TPPOH-1Tris, TPPOH-2Tris trans, TPPOH-2Tris cis, and TPPOH-3Tris) were 7.19 × 10–28 esu, 8.09 × 10–28 esu, 9.07 × 10–28 esu, and 7.24 × 10–28 esu, respectively. The γ values of the cis forms were found to be superior to those of all other compounds, indicating the significant role of the greater dipole moment and low symmetry of the cis form compared to other compounds. It was also found that the fluorescence intensity was decreased by 81.52%, 90.37%, 93.93%, and 84.62% for the hybrids TPPOH-1POM, TPPOH-2POM trans, TPPOH-2POM cis, and TPPOH-3POM with respect to their corresponding precursors, respectively, which reveals the Dawson-type POM as a strong quencher. This quenching phenomenon not only indicates again unequivocally the formation of hybrid compounds but also may imply a photoinduced electron/energy-transfer process favored from a porphyrin moiety to a Dawson-type POM moiety.