title: Site-selective imination of an anthracenone sensor: selective fluorescence detection of barium(II).
abstract: 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.
authors.affiliation: Department of Chemistry, University of South Dakota, Vermillion, South Dakota 57069, United States.
authors.forename: Prem N
authors.initials: PN
authors.lastname: Basa
authors.forename: Arundhati
authors.initials: A
authors.lastname: Bhowmick
authors.forename: Mariah M
authors.initials: MM
authors.lastname: Schulz
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Sykes
mesh_terms: D000873:Anthracenes / Q000138:chemical synthesis / Q000737:chemistry*; D001464:Barium / Q000032:analysis* / Q000737:chemistry; D001665:Binding Sites; D002623:Chemistry Techniques, Analytical / Q000295:instrumentation*; D007097:Imines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013379:Substrate Specificity
chemical_list: D000873:Anthracenes; D007097:Imines; D001464:Barium