Uranyl-Organic Coordination Compounds Incorporating Photoactive Vinylpyridine Moieties: Synthesis, Structural Characterization, and Light-Induced Fluorescence Attenuation

• Published in: Inorganic chemistry 2018-12, Vol.57 (23), p.14772-14785
• Main Authors: Wu, Si, Mei, Lei, Li, Fei-ze, An, Shu-wen, Hu, Kong-qiu, Nie, Chang-ming, Chai, Zhi-fang, Shi, Wei-qun
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b02523

The fluorescence of uranyl originated from electronic transitions (S11–S00 and S10–S0v, v = 0–4) of the ligand-to-metal charge transfer (LMCT) process is an intrinsic property of many uranyl coordination compounds. However, light-induced regulation on fluorescence features of uranyl hybrid materials through photoactive functional groups is less investigated. In this work, the photoactive vinyl group-containing ligands, (E)-methyl 3-(pyridin-4-yl)­acrylate and (E)-methyl 3-(pyridin-3-yl)­acrylate, have been used in the construction of uranyl coordination polymers in the presence of 1,10-phenanthroline (phen). Five compounds (UO2)3(μ3-O)­(μ2-OH)2(L1 )2(phen)2(1), (UO2)3(μ3-O)­(μ2-OH)3(L1 )­(phen)2 (2), (UO2)3(μ3-O)­(μ2-OH)3(L2 )­(phen)2 (3), [(UO2)2(μ2-OH)2(L2 )2(phen)2]·2H2O (4), and (UO2)­Zn­(SO4)­(phen)­(H2O)­(OH)2(5) were obtained under hydrothermal conditions. Compounds 1–4 are polynuclear uranyl structures with abundant π–π interactions and hydrogen bonds contributed to the 3D crystal packing of them. As model compounds, 1 and 3 are selected for exploring photoresponsive behaviors. The emission intensities of these two compounds are found to decrease gradually over the exposure time of UV irradiation. X-ray single crystal structural analysis suggests that the fluorescence attenuation can be explained by the slight rotation of pyridinyl groups around the carbon–carbon double bond during UV irradiation, which is accompanied by the change of weak interactions, i.e., π–π interactions and hydrogen bonds in strength and density. This feature of light-induced fluorescence attenuation may enable these two compounds to act as potential photoresponsive sensor materials.