Solution Properties and Effect of Anions on Third-Order Optical Nonlinearity of Porphyrin鈥揌eteropolyoxometalate Hybrid System

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• 作者：Zonghai Shi ; Yunshan Zhou ; Lijuan Zhang ; Sadaf ul Hassan ; Ningning Qu
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：March 27, 2014
• 年：2014
• 卷：118
• 期：12
• 页码：6413-6422
• 全文大小：478K
• 年卷期：v.118,no.12(March 27, 2014)
• ISSN：1932-7455

文摘

The investigation on interactions between tetraphenylporphyrin (TPP) and 伪-Keggin-type heteropolyoxometalates (POMs) (POMs sequentially refer to H₅PMo₁₀V₂O₄₀路36H₂O (PMoV), H₃PMo₁₂O₄₀路14H₂O (PMo), H₄SiMo₁₂O₄₀路xH₂O (SiMo), and H₄SiW₁₂O₄₀路xH₂O (SiW)) in THF reveals that TPP evolves into a monosalt and successively into a disalt by accepting protons from POMs and that the 2:1 hybrid between PMoV and TPP and the 1:1 hybrids between TPP and PMo, SiMo, and SiW are formed in the THF solution. The reaction equilibrium constants calculated for the 1:1 complexes are quite large, indicative of strong interaction between TPP and POMs. When the concentration of the reactants were simply increased, four hybrids [H₂TPP][H₄PMo₁₀V₂O₄₀]₂路6C₄H₄O路H₂O (1), [H₂TPP][HPMo₁₂O₄₀]路5C₄H₈O路5H₂O (2), [H₂TPP][H₂SiMo₁₂O₄₀]路3C₄H₈O路3H₂O (3), and [H₂TPP][H₂SiW₁₂O₄₀]路4C₄H₈O路8H₂O (4) were isolated and characterized. Z-scan measurement showed that POMs themselves had negligible nonlinear optical response, whereas they imposed remarkable effect on the third-order nonlinear optical properties of resulting TPP鈥揚OM hybrid systems. It is found that the second hyperpolarizability values of compounds 1鈥?b>4 are inversely proportional to the highest occupied molecular orbital鈥搇owest unoccupied molecular orbital (HOMO鈥揕UMO) gaps of these compounds and directly proportional to the discrepancy between the LUMO levels of TPP and POMs, i.e., the low-lying LUMO level of the POMs is important for the improved second hyperpolarizability value of the compounds.