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Based on fluorescent resonance energy transfer (FRET), we developed a ratiometric fluorescent probe 1 for sensing Cu 2+ . As expected, probe 1 exhibited high selectivity and excellent sensitivity in both absorbance and fluorescence detection of Cu 2+ in aqueous solution. A significant color change from pale yellow to pink could be observed, enabling naked-eye detection of Cu 2+ . Furthermore, fluorescence imaging experiment of Cu 2+ in living MGC-803 cells demonstrated its value of practical applications in biological systems. [ABSTRACT FROM AUTHOR]

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]