Asif Hafiz Muhammad, Zhou Yunshan, Zhang Lijuan, Shaheen Nusrat, Yang Di, Li Jiaqi, Long Yi, Iqbal Arshad, Li Yanqin
State Key Laboratory of Chemical Resource Engineering, Institute of Science, Beijing University of Chemical Technology , Beijing 100029, P. R. China.
Inorg Chem. 2017 Aug 21;56(16):9436-9447. doi: 10.1021/acs.inorgchem.6b03155. Epub 2017 Aug 10.
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.
合成了两种新型卟啉 - 多金属氧酸盐杂化物，即含有两个共价键合的Wells - Dawson型多金属氧酸盐（POMs）的[(CH)N]H[{COHNC(CHO)PVWO}CNH]·CHCN 1和含有一个共价键合的POM的[(CH)N)]H[COHNC(CHO)PVWO{CHN}]·CHCN 2，并通过元素分析、粉末XRD、FT - IR、H (P, V) NMR、MALDI - TOF - MS、紫外 - 可见光谱和循环伏安法测量对其进行了全面表征。实验结果表明，虽然所有化合物都表现出显著的三阶光学非线性，但杂化物1和2优于其相应的卟啉前体（对于54 - N - N'(1,3 - 四羟基 - 2 - (二羟甲基)丙烷 - 4 - 二基)苯 - 二酰胺，10,15,20 - 三苯基卟啉，其为杂化物1的前体，分子二阶超极化率γ = 8.0 × 10 esu；对于54 - N - (1,3 - 二羟基 - 2 - (羟甲基)丙烷 - 2 - 基)苯 - 酰胺，10,15,20 - 三苯基卟啉，其为杂化物2的前体，γ = 2.6 × 10 esu），并且杂化物1（γ = 12.9 × 10 esu）优于杂化物2（γ = 12.2 × 10 esu），这反映出更多与卟啉部分共价键合的POM部分对三阶光学非线性产生更显著的影响。同时，POMs连接到卟啉上导致显著的荧光猝灭（相对于其相应的卟啉前体，杂化物1的荧光强度降低了97%，杂化物2降低了80%），表明从卟啉部分到多金属氧酸盐部分有强烈的电子转移。杂化物较低的跃迁能量、单重态和三重态激发态之间较小的能量差以及更快的系间窜越（ISC）过程有利于增强杂化物1和2的非线性光学响应，这是由于当杂化物受到激光照射时，从卟啉部分到Dawson型POM部分的电子转移很容易发生，这也被认为是杂化物1优于杂化物2以及杂化物优于其相应卟啉前体的原因。
