Restriction of photoinduced twisted intramolecular charge transfer.

An intensive investigation of structure-property relationships in the aggregation-induced enhanced emission (AIEE) of luminescent compounds is essential for the rational design of highly emissive solid-state materials. In the AIEE-active compounds N,N'-bis[3-hydroxy-4-(2'-benzothiazolyl)phenyl]isophthalamide and N,N'-bis[3-hydroxy-4-(2'-benzothiazolyl)phenyl]-5-tert-butylisophthalamide, fast photoinduced twisted intramolecular charge transfer (TICT) of the enol excited state is found to be mainly responsible for the weak emission of their dilute solutions. The photoinduced TICT enol excited state is formed with a greatly distorted configuration, due to the large rotation about the C-N single bond. This facilitates nonradiative TICT decay from the normal enol excited state to the highly twisted enol excited state, rather than proton-transfer decay to the keto excited state. In aggregates, photoinduced nonradiative deactivation of TICT is strongly prohibited, so that excited-state intramolecular proton transfer (ESIPT) becomes the dominant decay, and hence contributes greatly to the subsequent emission enhancement of the keto form. Molecular design and investigation of analogous single-armed compounds further verifies this kind of AIEE mechanism.

Fluorescence turn on of coumarin derivatives by metal cations: a new signaling mechanism based on C=N isomerization.

[reaction: see text] A new sensing mechanism based on C=N isomerization, which shows a very significant fluorescence enhancement to the metal cations in a simple and efficient way, is demonstrated. A coumarin derivative (L) containing a C=N group was designed as an example for illustration. The free ligand L is almost nonfluorescent due to the isomerization of C=N double bond in the excited state. However, the solution of ligand shows about a 200-fold increase of fluorescence quantum yield (about 30%) upon addition of Zn(ClO4)2.

An efficient chloride-selective fluorescent chemosensor based on 2,9-bis(4'-hydroxyphenyl)phenanthroline Cu(II) complex.

A new complex Cu(II)/L, composed of 2,9-bis(4'-hydroxyphenyl)phenanthroline (L) and Cu(II), was synthesized as an efficient chloride-detection fluorescent chemosensor with high selectivity and sensitivity over other halide anions, F(-), Br(-), I(-). The recognition mechanism was discussed primarily.

Novel fluorescent sensor for detection of Cu(II) in aqueous solution.

A novel fluorescent chemosensor based on aminonaphthol, which can selectively recognize copper(II) over other metal ions in aqueous solution within a broad pH span, was synthesized.

New fluorescent chemosensor based on exciplex signaling mechanism.

[reaction: see text]. A novel fluorescent chemosensor (compound 1) containing aminonaphthol, which selectively recognizes fluoride anion with high sensitivity, was synthesized. The fluorescence of compound 1 was quenched rapidly by fluoride ion, and a new peak at a longer wavelength emerged concurrently, which constituted the signature for fluoride detection. The mechanism of exciplex formation was proposed for the interesting observation.

Large-scale fabrication and characterization of Cd-doped ZnO nanocantilever arrays.

We demonstrate bulk synthesis of highly crystalline Cd-doped ZnO nanocantilever arrays (CZNAs) using Cd and Zn powders at 600 degrees C, which is characterized via scanning electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy, selected area electron diffraction, and high resolution TEM. The results show that the as-prepared CZNAs have diameters of about 15-50 nm, and lengths up to 400 nm and the corresponding process of growth is suggested for conventional vapor solid mechanism.

An effective fluorescent chemosensor for the detection of copper(II).

The fluorescent compound N-substituted 2,6-bis(benzimidazol-2-yl)pyidine (1) has been synthesized. The fluorescent characteristics of the compound 1 and 2,6-bis(benzimidazol-2-yl)pyidine (2) and the complexes formed between the two compounds and different metal ions have also been investigated. The results show that the compound 1 possesses a specific ability to form complex with Cu(2+) ion, but the compound 2 have not such a property. It is proposed that the specific recognition ability of compound 1 to Cu(2+) may be attributed to the cyclic configuration of this compound in polar solvent.

A novel colorimetric and fluorescent anion chemosensor based on the flavone quasi-crown ether-metal complex.

The metal-ligand complex 1 ([Mg (L)] (2+)) (or 2 ([Ca (L)]( 2+))) was demonstrated to selectively bind HSO(4)(-) (or H(2)PO(4)(-)) over other anions by using UV-vis absorption and fluorescence spectroscopy. The studied complex exhibits the remarkable color change and fluorescence quenching upon introducing HSO(4)(-) (or H(2)PO(4)(-)) anion in acetonitrile. Both the mechanism and structure of the secondary complex of complex 1 with anion were proposed on the basis of theoretical computation.