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A new fluorescent sensor 6-(2,3-dihydroxyphenyl)-5,6-dihydrobenzoimidazo[1,2-c] quinazoline (H 2 L) and the Zn(II) complex [Zn 2 L 1 2 ]∙C 2 H 5 OH (H 2 L 1 = 3-{[2-(1 H -benzoimidazol-2-yl)-phenylimino]-methyl}-benzene-1,2-diol) ( 1 ) were synthesized and characterized by single-crystal X-ray diffraction. H 2 L can be used to recognize Cu 2+ in aqueous media as an on–off fluorescent sensor, forming the Cu(II) Schiff-base complex (CuL 1 ). Furthermore, CuL 1 can serve as an off–on fluorescent sensor to detect histidine (His) via the ligand displacement approach. The sequential detection of Cu(II) and histidine shows on–off–on phenomenon. The crystal structure of the dinuclear Zn(II) complex indicates that the coordination of H 2 L with Zn(II) promotes C N bond breakage, resulting in the quinazoline ring-opening of H 2 L to form the Zn(II) Schiff-base complex ( 1 ). The experimental results proved that H + can also assist the ring-opening of H 2 L to form a Schiff base, H 2 L 1 . H 2 L is stable in neutral and weak basic solutions. This is further confirmed by the theoretical calculations. The cell imaging studies indicated that H 2 L and CuL 1 can be used to detect the intracellular Cu 2+ ion and His under physiological conditions, respectively. CuL 1 can also be used to determine His in urine. [ABSTRACT FROM AUTHOR]

A chemosensor 3-[(2-hydroxybenzylidene)-amino]-1H-pyridin-2-one (HL) for multi-ions was synthesized and characterized by single-crystal X-ray diffraction. HL is a turn-on fluorescence chemosensor for Al 3+ , F − , and CN − ions in DMSO. F − and CN − anions could be further distinguished by the ratiometric absorption spectrometry method. Job plot and 1 H NMR data showed that the binding stoichiometries of HL with Al 3+ , F − , or CN − all were 1:1. Further observations of 1 H NMR titration and ESI-MS showed that the possible fluorescent species of Al 3+ with HL was [AlL(OH)(DMSO) 2 ] + in DMSO. The spectroscopic observations of the Al(III) complex showed that the two oxygen atoms and one imine nitrogen atom of HL were coordinated to the Al(III) ion. While the crystal structure of the Ni(II)-L complex confirmed the tridentate coordination mode of HL in the complexes. The experimental results revealed that HL and F − ion formed hydrogen bond in DMSO, while CN − attacked the carbon atom at –C N of HL to undergo a nucleophilic addition. The theoretical calculations confirmed that HL showed very weak fluorescence because of the excited-state intramolecular proton transfer (ESIPT). The turn-on sensing of HL to Al 3+ , F − , and CN − ions arose from the inhibition of ESIPT. MTT tests showed that HL was low toxic to cells. Also, HL could probe intracellular Al 3+ and F − ions by bioimaging. [ABSTRACT FROM AUTHOR]