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Selective reduction of an anthracenone-quinoline imine derivative, 2, using 1.0 equiv of NaBH(4) in 95% ethanol affords the corresponding anthracen-9-ol derivative, 3, as confirmed by (1)H NMR, (13)C NMR, ESI-MS, FTIR, and elemental analysis results. UV-vis and fluorescence data reveal dramatic spectroscopic changes in the presence of Zn(II) and Cu(II). Zinc(II) coordination induces a 1,5-prototropic shift resulting in anthracene fluorophore formation via an imine-enamine tautomerization pathway. Copper(II) induces a colorimetric change from pale yellow to orange-red and results in imine hydrolysis in the presence of water. Spectroscopic investigations of metal ion response, selectivity, stoichiometry, and competition studies all suggest the proposed mechanisms. ESI-MS analysis, FTIR, and single-crystal XRD further support the hydrolysis phenomenon. This is a rare case of a single sensor that can be used either as a chemosensor (reversibly in the case of Zn(II)) or as a chemodosimeter (irreversibly in the case of Cu(II)); however, the imine must contain a coordinating Lewis base, such as quinoline, to be active for Cu(II).

Site-selective imination of anthraquinone-based macrocyclic crown ethers using titanium tetrachloride as the catalyst yields imines where only the external carbonyl group of the anthraquinone forms Schiff-bases. The following aromatic amines yield monomeric compounds (aniline, 4-nitroaniline, 4-pyrrolaniline, and 1,3-phenylenediamine). Reaction of 2 equiv of the macrocyclic anthraquinone host with 1,2- and 1,4-phenylenediamine yields dimeric imine compounds. The 1,2-diimino host acts as a luminescence sensor, exhibiting enhanced selectivity for Ba(II) ion. Spectroscopic data indicate that two barium ions coordinate to the sensor. Due to E/Z isomerization of the imine, the monomeric complexes are nonluminescent. Restricted rotation about the 1,2 oriented C═N groups or other noncovalent/coordinate-covalent interactions acting between neighboring crown ether rings may inhibit E/Z isomerization in this example, which is different from current examples that employ coordination of a metal cation with a chelating imine nitrogen atom to suppress E/Z isomerization and activate luminescence. The 1,4-diimino adduct, where the crown rings remain widely separated, remains nonluminescent.