The Effect of 蟺 Contacts between Metal Ions and Fluorophores on the Fluorescence of PET Sensors: Implications for Sensor Design for Cations and Anions

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• 作者：Joseph W. Nugent ; Hyunjung Lee ; Hee-Seung Lee ; Joseph H. Reibenspies ; Robert D. Hancock
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：September 2, 2014
• 年：2014
• 卷：53
• 期：17
• 页码：9014-9026
• 全文大小：607K
• ISSN：1520-510X

文摘

The idea that M路路路C 蟺 contacts between diamagnetic heavy metal ions such as Pb(II), Ag(I), Pd(II), or Hg(II) and the anthracenyl fluorophore of adpa ((N-(9-anthracenylmethyl)-N-(2-pyridinylmethyl)-2-pyridinemethanamine) are responsible for quenching the fluorescence of the complexes of these metal ions with adpa is explored crystallographically. The structures of [Pb(adpa)(NO₃)₂] (1), [Ag(adpa)NO₃] (2), [Pd(adpa)NO₃]NO₃ (3), [Zn(adpa)(NO₃)₂] (4), and [Cd(adpa)Br₂] (5) are reported. The 蟺 contacts with the fluorophore are for 1 are a Pb路路路C 蟺 contact of 3.178 脜; for 2, an Ag路路路C 蟺 contact of 3.016 脜; and for 3, a Pd路路路C 蟺 contact of 2.954 脜 on the axial site of the Pd(II) ion. The Zn(II) ion in 4 has no Zn路路路C 蟺 contact, with the anthracenyl fluorophore rotated completely away from the Zn(II) ion. These structures confirm that in the Pb(II), Ag(I), and Pd(II) complexes of adpa, which experience strong quenching of fluorescence, there are strong M路路路C 蟺 contacts, as expected if it is the 蟺 contacts that quench fluorescence. In contrast, for the Zn(II) adpa complex, which forms no 蟺 contact, there is a strong increase in fluorescence intensity. The structure of 5 shows a long Cd路路路C 蟺 contact at 3.369 脜, in contrast to a previously reported structure with two coordinated nitrates where the Cd路路路C 蟺 contact is 3.097 脜. The long Cd路路路C 蟺 contact in [Cd(adpa)Br₂] suggests how coordination of Br^{鈥?/sup>, as well as other more covalently bound ligands such as Cl鈥?/sup>, SCN鈥?/sup>, and S₂O₃2鈥?/sup>, cause an increase in fluorescence intensity, reported for the Cd(II)adpa complex in 50% CH₃OH/H₂O. Coordination of covalently bound ligands to the Cd(II) weakens the Cd路路路C 蟺 contact and so enhances fluorescence, whereas more ionically bound ligands such as SO₄2鈥?/sup>, NO₃鈥?/sup>, or H₂O produce a strong Cd路路路C 蟺 contact and weakened fluorescence. Complexes of the Cd(II)/adpa type may form the basis for a new type of anion/small molecule sensor. The tendency of metal ions to form 蟺 contacts with aromatic groups is analyzed in terms of the frequency of occurrence of 蟺 contacted structures in the literature, as well as by DFT calculations on the adpa complexes.}