American Chemical Society
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Luminescence Detection of Transition and Heavy Metals by Inversion of Excited States:  Synthesis, Spectroscopy, and X-ray Crystallography of Ca, Mn, Pb, and Zn Complexes of 1,8-Anthraquinone-18-Crown-5

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posted on 2006-01-23, 00:00 authored by Mariappan Kadarkaraisamy, Andrew G. Sykes
A lumophore composed of anthraquinone attached to a macrocyclic polyether ring containing an intraannular carbonyl is capable of selectively detecting Pb2+ ion in solution using an alternative photophysical detection mechanism. Of the various methods available for detection of ions in solution, a mechanism involving inversion of excited states has not been previously employed for the detection of transition and heavy metals. In this mechanism, nonradiative n−π* transitions are replaced by radiative π−π* transitions upon complexation by a suitable guest cation. Optimum fluorescence enhancement is achieved using cations of high charge, large cations that form long bonds within the host, and cations which do not coordinate solvent or the counteranion, all of which are necessary for inversion of excited states to occur. Photophysical properties and binding constants of this new class of luminescence sensors are provided, as well as the X-ray crystallographic results for Pb2+, Mn2+, and Zn2+ complexes of 1,8-oxybis(ethylene-oxyethyleneoxy)anthracene-9,10-dione (1), referred to as 1,8-anthraquinone-18-crown-5. ([1·Pb](ClO4)2 (2) (monoclinic, P21/n, a = 8.0303(6) Å, b = 25.976(2) Å, c = 12.1616(9) Å, β = 94.956(1)°, Z = 4, 4980 reflections [I ≥ 2σ(I)], R1 = 0.0266, wR2, 0.0500, 173(2) K). [1·Mn(H2O)(NCCH3)](ClO4)2 (5) (monoclinic, P21/c, a = 10.132(2) Å, b = 11.8030(4) Å, c = 23.999(7) Å, β = 95.75(2)°, Z = 4, 3000 reflections [I ≥ 2σ(I)], R1 = 0.0488, wR2, 0.0938, 203(2) K). [1·Zn(H2O)(NCCH3)](ClO4)2 (6) (monoclinic, P21/c, a = 10.177(10) Å, b = 11.977(6) Å, c = 24.166(4) Å, β = 95.83(4)°, Z = 4, 3061 reflections [I ≥ 2σ(I)], R1 = 0.0673, wR2, 0.1729, 295(2) K).)