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Three AIE (aggregation-induced emission)-ESIPT (excited-state intramolecular proton transfer) active 2-(2-hydroxyphenyl)benzothiazole derivatives, HL 1 , HL 2 and HL 3 with one, two and three rotatable phenyl groups, were obtained and characterized. Their AIE properties in THF/HEPES solution were investigated in detail. HL 2 shows the best AIE performance with 71-fold fluorescence enhancement, while HL 3 only shows a 9-fold enhancement. With the AIE property, HL 1 and HL 2 could act as fluorescence chemosensors to detect Cu 2+ ions via the "turn off" mode in THF/HEPES media. With the ESIPT property, HL 1 and HL 2 could also detect Zn 2+ ions via the "turn on" mode in EtOH/HEPES media. During the detection process, both demonstrate rapid response and high contrast before and after the addition of metal ions. The species formed in the detection system were investigated. The results of X-ray single-crystal diffraction confirm that Zn 2+ is coordinated with the oxygen atom and Schiff base nitrogen atom instead of the benzothiazole nitrogen atom in the tetrahedron geometry. Moreover, the chemosensors were successfully constructed into handy fluorescence test papers for Cu 2+ and Zn 2+ detection.

A multi-binding site chemosensor, N-(3-methoxy-2-hydroxybenzylidene)-3-hydroxy-2-naphthahydrazone (H 3 L), with excited-state intramolecular proton transfer (ESIPT) behaviour was prepared and characterized. It possesses no aggregation-induced emission (AIE) characteristics but can detect Cd 2+ and Zn 2+ ions selectively in the "off-on" mode based on the AIE of their complexes in the media of THF/HEPES and THF/H 2 O, respectively, which will provide a new strategy for target detection based on AIE. The detection limits of Zn 2+ and Cd 2+ were 9.85 × 10 -9 M and 1.27 × 10 -7 M, respectively. The aggregates of the complexes formed in the detection system were confirmed by DLS data and SEM images. The corresponding Zn 2+ (1) and Cd 2+ (2) complexes were prepared to investigate the response mechanism. Powder X-ray diffraction and single crystal X-ray diffraction proved that complex 1 is the species formed in the detection system. The chemosensor coordinates with the Cd 2+ and Zn 2+ ions in different formation and coordination modes, leading to the emission position of the aggregates at 560 and 645 nm, respectively, based on which Cd 2+ ions were successfully differentiated from Zn 2+ ions. Moreover, the detection of Cd 2+ and Zn 2+ ions was realized qualitatively via test paper and quantitatively in water.

A D-π-A Schiff-base compound, 2-amino-3({[4-(diethylamino)-2-hydroxylphenyl]methylene}amino)-but-2-enedinitrile (H2L), was prepared using diaminomaleonitrile and 4-(N,N-diethylamino)salicylaldehyde. Compared with H2L at 293 K, a low temperature of 100 K makes the parallel aromatics in H2L come closer and fluorescence emission becomes weaker because of π-π interaction-caused quenching. After grinding the crystals of H2L, the colour changed from dark brown-red to yellow under room light and the fluorescence emission enhanced about 9-fold due to the damage of the intermolecular hydrogen bonds, leading to a decrease of non-radiative transition. H2L showed aggregation-induced emission enhancement (AIEE) characteristics in THF/H2O, whose mechanism is attributed to the restriction of intramolecular rotation (RIR). The UV-Vis spectra of H2L with Cu2+ in THF/H2O showed that at first a CuL complex was formed and subsequently a CuL' complex (H2L' = N',N'-bis(4-N',N'-diethylsalicylidene) ethylenediamine) was obtained. The CuL complex turned into the CuL' complex as time prolonged. H2L acted as a dual channel chemosensor for Cu2+ ions in THF/HEPES (v/v: 2 : 8, pH = 8.0) and the CuL complex was stable in this medium. H2L is also a naked-eye probe for Mn2+ ions in CH3CN. The limits of detection are much lower than the allowable level of copper(ii) and manganese(ii) in drinking water set by the World Health Organization (WHO).

The compounds of 3-aminopyridine-2-carboxylic acid with K(+) (1) and Zn(2+) (2) were found to be AIE-active. The AIE behaviours could be attributed to the restriction of intramolecular rotation (RIR) and vibration (RIV) via hydrogen bonds, resulting in rigidity enhancement of the molecules. An AIE-based fluorescence turn on chemosensor for the Zn(ii) ion has been developed in aqueous media with high selectivity and sensitivity.

A quinazoline-based fluorescence chemosensor, 6-phenol-2-yl-(5,6-dihydrobenzimidazo[1,2-c])quinazoline (HL), for highly selective recognition of Cu(II) in aqueous media was synthesized. The detection limit was of the order of 10(-6) M. The crystal structures of the Cu(II) and Cd(II) complexes showed that HL changed to a Schiff base when it reacts with metal salts and that the metal ions coordinate with two nitrogen atoms and one hydroxyl oxygen atom from the Schiff base. The theoretical calculations at B3LYP-SCRF/6-31G(d) confirmed that it is the Cu(II) ion that assisted the ring-opening of the quinazoline derivative, forming a Cu(II) Schiff base complex during the detection. LMCT leads to the disappearance of fluorescence. A cell imaging study indicated that HL could be used to detect the intracellular Cu(2+) ion.

Two new Schiff base complexes, [ZnL(Ac)]2 (1) and [CuLCl]·H2O (2) (HL = 2-(2'-hydroxynaphthylmethylene)aminophenylbenzimidazole, Ac = acetate) were synthesized by a one-pot reaction and characterized by elemental analyses, IR and single-crystal X-ray diffraction. Fluorescence of complex 1 showed "on-off-on" switching when Cu(2+) and cyanide were sequentially detected. This phenomenon was investigated by UV-Vis absorption, fluorescence and ESI-MS spectra, and theoretical calculations to explain the response. Complex 1 can selectively respond to Cu(2+) with the fluorescence "turn-off" owing to the formation of complex 2 in the solution. Interestingly, the quenched fluorescence of complex 1 by Cu(2+) ions could be turned on after the addition of cyanide owing to the displacement of L(-) by CN(-) to form [Cu(CN)x](n-), making complex 1 a selective CN(-) probe. In addition, the results of the MTT assay experiment indicate that complex 1 has a low toxicity to cells and can be used to detect intracellular Cu(2+) ion by live cell imaging.

A tetrazole derivative 1-[(1H-tetrazol-5-ylimino)methyl]naphthalen-2-ol (H2L) as a fluorescent chemosensor for Al(3+) in DMSO and Zn(2+) in DMF was designed and synthesized. From (1)H NMR data, the Job plot and the ESI-MS spectrum, 1 : 1 stoichiometric complexation between H2L and Al(3+)/Zn(2+) was found in DMSO and DMF, respectively. The theoretical calculations at the level of B3LYP/6-311G** for the ground state and TD-B3LYP/6-311G** for the excited state revealed the sensing mechanism is the inhibition of excited state intramolecular proton transfer (ESIPT). And the possible fluorescent species formed in the DMSO and DMF solutions were deduced to be [Al(HL)(OH)(NO3)(H2O)(DMSO)] and [Zn(HL)(OH)(H2O)(DMF)]. What's more, it is confirmed that H2L could be used to detect Al(3+) and Zn(2+) in cells by bioimaging.

Hydro- and solvo-thermal reactions of d-block metal ions (Mn(2+), Co(2+), Zn(2+) and Cd(2+)) with monosodium 2-sulfoterephthalate (NaH(2)stp) form six 3D coordination polymers featuring cluster core [M(4)(μ(3)-OH)(2)](6+) in common: [M(2)(μ(3)-OH)(stp)(H(2)O)] (M = Co (1), Mn (2) and Zn (3)), [Zn(2)(μ(3)-OH)(stp)(H(2)O)(2)] (4), [Zn(4)(μ(3)-OH)(2)(stp)(2)(bpy)(2)(H(2)O)]·3.5H(2)O (5) and [Cd(2)(μ(3)-OH)(stp) (bpp)(2)]·H(2)O (6) (stp = 2-sulfoterephthalate, bpy = 4,4'-bipyridine and bpp = 1,3-di(4-pyridyl)propane). All these coordination polymers were characterized by single crystal X-ray diffraction, IR spectroscopy, thermogravimetric and elemental analysis. Complexes 1-3 are isostructural coordination polymers with 3D frameworks based on the chair-like [Zn(4)(μ(3)-OH)(2)](6+) core and the quintuple helixes. In complex 4, there exist double helixes in the 3D framework based on the chair-like cluster cores. Complex 5 possesses a 2-fold interpenetration structure constructed from boat-like cluster core and the bridging ligands stp and bpy. For complex 6, the chair-like cluster cores and stp ligands form a 2D (4,4) network which is further pillared by bpp linkers to a 3D architecture. Magnetic studies indicate that complex 1 exhibits magnetic ordering below 4.9 K with spin canting, and complex 2 shows weak antiferromagnetic coupling between the Mn(II) ions with g = 2.02, J(wb) = -2.88 cm(-1), J(bb) = -0.37 cm(-1). The fluorescence studies show that the emissions of complexes 3-6 are attributed to the ligand π-π* transition.

Self-assembly of copper(ii) ion, 3,4-pyridinedicarboxylate (PDC), and 1,10-phenanthroline (phen) under basic conditions at 100 °C affords four PDC linked copper(ii) complexes, [Cu(4)(μ(2)-OH)(3)(μ(3)-OH)(PDC)(phen)(4)](n)·n(PDC)·11.5 nH2O (1), [Cu(4)(μ(2)-OH)(2)(μ(3)-OH)(2)(PDC)(phen)(4)](n)·n(PDC)· 11.5 nH(2)O (2), [Cu(8)(μ(2)-OH)(2)(μ(3)-OH)(6)(PDC)(2)(phen)(8)]·2(PDC)·23 H(2)O (3), and [Cu(3.5)(μ(2)-OH)(3) (PDC)(2)(phen)](n) (4). 1-4 are copper hydroxo complexes, and 1, 2 and 3 co-crystallized from the one-pot reaction. X-ray single crystal diffraction analyses indicate that complexes 1 and 2 are linkage isomers and contain tetranuclear copper cluster cores with different geometry, and that PDC links the cluster core to form a one-dimensional chain. Complex 3 is a discrete step-like octanuclear copper hydroxo cluster complex. The involvement of hydroxo and phen in the coordination makes some coordination sites of PDC idle, which leads to rich hydrogen bonds and π-π interactions in complexes 1, 2 and 3. Complex 4 contains two types of copper hydroxo cluster cores: chair-like tetranuclear and linear trinuclear units, and the cluster cores are linked by PDC to a double-layer metal-organic framework. Magnetic properties of 1, 3 and 4 were investigated. The results reveal that complexes 3 and 4 exhibit strong antiferromagnetic interactions whereas ferromagnetic coupling is predominant for complex 1. The magnetic properties are analyzed in connection with their structures.