Longmei Yang

Complex‐Formation‐Enhanced Fluorescence Quenching Effect for Efficient Detection of Picric Acid

Amine-functionalized α-cyanostilbene derivatives (Z)-2-(4-aminophenyl)-3-(4-butoxyphenyl)acrylonitrile (ABA) and (Z)-3-(4-butoxyphenyl)-2-[4-(butylamino)phenyl]acrylonitrile (BBA) were designed for specific recognition of picric acid (PA), an environmental and biological pollutant. The 1:1 host-guest complexes formed between the chemosensors and PA enhanced fluorescence quenching, thus leading to sensitive and selective detection in aqueous media and the solid phase.

Synthesis of two novel indolo[3,2-b]carbazole derivatives with aggregation-enhanced emission property

Luminogenic materials with AIE (aggregation-induced emission) and AIEE (aggregation-induced enhanced emission) characteristics have attracted substantial research interest due to their potential applications in optics, electronics environmental and the biological sciences. Here, we successfully synthesized two novel indolo[3,2-b]carbazole derivatives (compounds 3 and 4) with strong symmetrical groups, which were demonstrated to exhibit superior AIEE properties. Both 3 and 4 contain the same π-conjugated core structure, but slightly differ in the cyano-substituted stilbene group, giving rise to a high charge mobility, similar optical properties and energy band-gaps. The bulky cyano group attached to a vinylene moiety generates intramolecular co-planarity and prevents π–π stacking, whereby the emission in the aggregates can be enhanced. In addition, it is found that the cyano group also plays an important role in the formation of J-type aggregation, which is advantageous to the appearance of AIE and/or AIEE properties. A slight modification of the terminal substituent group renders compounds 3 and 4 AIEE properties entirely. As revealed by crystallographic data, the multiple intermolecular hydrogen bonding in 4 restricts intramolecular vibration and rotation, which enables 4 to emit intensely in the solid state. Moreover, cyano groups endow 3 with an improved self-assembly ability under the proper conditions. The molecules of 3 self-organize into one-dimensional ordered microfibers and/or nanorods that show a significant optical waveguide with different water fractions, indicating that the aqueous suspension of microfibers favors fluorescence emission. Our results demonstrate that the AIEE properties of the novel indolo[3,2-b]carbazole derivatives are highly related to the molecular structure and aggregate packing.

A small-molecule chemosensor for the selective detection of 2,4,6-trinitrophenol (TNP)

A pyridine-based small-molecule receptor (L) for the specific recognition of TNP was synthesised and characterised by 1H NMR, 13C NMR and FT-IR spectra, and the optical properties were studied by UV-Vis absorption and PL spectra. The results showed that the fluorescence of L was strongly quenched by picric acid accompanied by an obvious colour change from transparent to yellow, which indicated that the receptor L can serve as a small-molecule sensor for TNP. Crystal structure determination and theoretical calculation of the corresponding host–guest complex L·TNP were also performed.

Multi-stimuli-responsive fluorescence of a highly emissive difluoroboron complex in both solution and solid states

A highly fluorescent emissive difluoroboron complex (TC) was designed, synthesized and characterized. The absolute fluorescence quantum yields of TC are 33.0% in the solid state and 26.0% in the solution state. The results of X-ray diffraction analysis demonstrate that the rigid structure, the intermolecular hydrogen bonding and the well-ordered as well as loose molecular packing are the major reasons for the high fluorescence emission. Moreover, the colors and fluorescence emission of TC can be switched by external stimuli including grinding and acids/bases. Powder X-ray diffraction (PXRD) investigation verifies that the crystalline–amorphous state transformation between the original and ground states might be attributed to the mechanochromic luminescence properties. The high fluorescence emission and multi-stimuli-responsive fluorescence properties reveal that TC can be used as rewritable information storage, security ink and a fluorescence indicator for acids/bases.

A simple pyridine-based colorimetric chemosensor for highly sensitive and selective mercury(II) detection with the naked eye

Two easily-prepared pyridine-based derivatives of (Z)-2-(4-amino-phenyl)-3-(pyridine-4-yl)acrylonitrile (I)and (Z)-2-phenyl-3-(pyridin-4-yl)acrylonitrile (II) were designed, synthesised and characterised. Due to the formation of a complex with Hg2+, hence leading to an enhanced ICT effect, I exhibits a visible colour change from light yellow to orange, rendering it suitable for use as a naked-eye sensor for rapid detection of Hg2+ in an aqueous ethanol solution. When mixed with Hg2+, I interacts with Hg2+ in a2:1 (Y1-Hg2+) stoichiometry via a coordination bond with an association constant of 7.7 × 108 M−2 (R2 = 0.96). The present probe I exhibits excellent reproducibility, reversibility, sensitivity and selectivity with the presence of low concentration of Hg2+ (1.74 × 10−10 M).

Two polymorphs and cocrystal of styryl-pyridine derivatives with tuned emission induced by Co2+ and Zn(phen)32+

A styryl-pyridine derivative, 2,5-dibutoxy-1,4-bis[2-(4-pyridyl)ethenyl]benzene (L), has been designed and synthesised. Two polymorphs of L and crystals of [Zn(phen)3]2L(ClO4)4 were obtained by different crystallisation conditions. Polymorph-α was prepared by a solvent evaporation method. However, polymorph-β and a cocrystal of [Zn(phen)3]2L(ClO4)4 were obtained by different inducing reagents. It has been found that there are, in total, four independent conformations of the molecule L in the three kinds of crystals. We have calculated the standard molar enthalpy of formation (ΔHm) of each conformation and demonstrated that the stabilisation energy of each conformation significantly relies on both the planarity of the molecules (L) and bond length of conjugated bridges. Furthermore, the photophysical properties of the three kinds of crystals also exhibit differences in the vibration and absorption spectroscopies, solid-state photoluminescence and time-resolved fluorescence, which may arise from the chromophores stacking modes and the intermolecular electronic interactions in the crystals. These results revealed that the optical properties of functional organic materials could be tuned by controlling their crystallisation environment for a specific molecule.

The self-aggregation of fluorophore-triphenylamine nanostructures with tunable luminescent properties: the effect of acidity and rare earth ions

A D–π–A type triphenylamine derivative 3-(4-(diphenylamino)phenyl)acrylic acid (abbreviated as L) is designed, synthesized and characterized by single crystal X-ray diffraction analysis. The self-aggregation of L nanostructures in different acidity aqueous solutions and/or under the guidance of rare earth (RE) ions is studied, along with the corresponding optical properties. In strong acidic conditions, L molecules self-assemble to form two dimensional nanostructures. While in neutral aqueous solutions, L tends to form nanorods. In the strong alkali environment, nanofibers were obtained. Moreover, in acidic conditions, the existence of Tm3+ induces the L molecules to self-aggregate into nanoplates. Flower-like six branched structures are observed when Yb3+ is used. The changed morphology leads to tunable linear optical properties.