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

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).)