Controlling the Fluorescence Response of PET Sensors via the Metal-Ion 蟺-Contacting Ability of the Fluorophore: Coumarin, a Weaker 蟺 Contacter

详细信息    查看全文

• 作者：Joseph W. Nugent ; Joseph H. Reibenspies ; Robert D. Hancock
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：October 19, 2015
• 年：2015
• 卷：54
• 期：20
• 页码：9976-9988
• 全文大小：741K
• ISSN：1520-510X

文摘

The 蟺-contact hypothesis, that quenching of the fluorescence of complexes of photoinduced electron transfer sensors with heavy diamagnetic metal ions may be caused by 蟺 contacts between the metal ion and the fluorophore of the sensor, is examined with a study of the fluorescent properties of the sensor 4-[[bis(2-pyridinylmethyl)amino]methyl]-6,7-dimethoxy-1-benzopyran-2-one (cdpa) and the structures of its complexes with some metal ions. The coumarin-type fluorophore of cdpa is a weaker 蟺-contact former than the anthracenyl fluorophore of the analogue adpa (Inorg. Chem. 2014, 53, 9014): only Ag^I, the strongest 蟺 contact former, quenches the fluorescence of cdpa, apart from paramagnetic Cu^II and Ni^II, which quench fluorescence by a redox mechanism not requiring 蟺 contacts. The structures of [Ag(cdpa)NO₃] (1), [Pb(cdpa)(NO₃)₂] (2), [Zn(cdpa)(NO₃)₂] (3), [Cd(cdpa)Cl₂]₂ (4), [Cd(cdpa)₂H₂O](NO₃)₂ (5), and [Hg(cdpa)₂H₂O](NO₃)₂ (6) are reported. Structure 1 shows that Ag^I is the only metal ion studied that forms 蟺 contacts with the fluorophore of cdpa in the solid state: Ag路路路C 畏² 蟺 contacts of 3.083 and 3.095 脜, in line with quenching of the fluorescence of the Ag^I(cdpa) complex. In contrast, Pb^II, Zn^II, and Cd^II show chelation-enhanced fluorescence in their cdpa complexes, and the structures of 2鈥?b>4 show that the fluorophore of cdpa in each case forms no 蟺 contacts. By contrast, the adpa complexes of Pb^II and Cd^II show 蟺 contacts with its more strongly 蟺-contacting fluorophore (Inorg. Chem. 2014, 53, 9014). The structures of 5 and 6 show bis-complexes of cdpa: the coordination geometries of Cd^II and Hg^II are discussed in relation to the number of covalently bound donor atoms present. The preferred hapticity of 蟺-contacted metal ions is evaluated from the literature structures, suggesting that d¹⁰ metal ions such as Ag^I and Hg^II, and tetragonally distorted Cu^II and Pd^II, prefer 畏¹ and 畏² 蟺 contacts, while more ionically bound metal ions such as K^I, Ba^II, and La^III, as well as d¹⁰s² metal ions such as Tl^I, Pb^II, and Bi^III, prefer 畏⁶ contacts.