Weiju Zhu

A new carbazole-based Schiff-base as fluorescent chemosensor for selective detection of Fe3+ and Cu2+.

A new carbazole-based Schiff-base (1) as a multi-functional fluorescent chemosensor was designed, synthesized and characterized, which can selectively recognized Fe(3+) and Cu(2+) ions over a number of other metal ions. Compound 1 could detect Fe(3+) and Cu(2+) by UV-Vis method and fluorescence method. The stoichiometry ratio of 1-Fe(3+) and 1-Cu(2+) are 2:1 and 1:1, respectively, by the method of Jobs plot. Moreover, the detection limits were calculated to be 4.23×10(-6) mol/L for Fe(3+) ion and 5.67×10(-6) mol/L for Cu(2+) ion. In the presence of Fe(3+)/Cu(2+) ions, the fluorescence enhancement was attributed to the inhibited C=N isomerization and the obstructed excited state intramolecular proton transfer (ESIPT) of compound 1. At the same time, the interactions of compounds 1 with other ions were also investigated and unobvious UV-Vis absorption and fluorescence spectral changes were observed. Thus a new kind of chemosensor for Fe(3+)/Cu(2+)with high sensitivity and selectivity was introduced.

Difunctional chemosensor for Cu(II) and Zn(II) based on Schiff base modified anthryl derivative with aggregation-induced emission enhancement and piezochromic characteristics

Three new anthryl Schiff base derivatives containing a similar molecular structure were synthesized through a simple method and their fluorescent properties were investigated in detail. Among these, compound 1 displayed an aggregation-induced emission (AIE) feature, 2 exhibited an aggregation-induced emission enhancement (AIEE) property, while 3 showed aggregation-caused quenching (ACQ) behavior. Single-crystal structure and theoretical calculation analysis show that the larger conjugation and the existence of multiple intra- and intermolecular interactions restricts the intramolecular vibration and rotation, which benefit the emission in the condensed state, while the tight dimer structure and intramolecular torsional motion induce fluorescence quenching. Moreover, compound 2 can be utilized as fluorescence on–off type sensor for Cu2+ in methanol–H2O (4/1, v/v, pH 7.2) HEPES buffer solution, as well as fluorescence off–on type sensor for Zn2+ in pure methanol solution. The 2 : 1 ligand-to-metal coordination pattern of the 2-Cu2+ and 2-Zn2+ were calculated through a Jobs plot, and were further confirmed by X-ray crystal structures of complexes 2-CuBr2 and 2-ZnCl2. In addition, 2 also exhibits a piezofluorochromic characteristic.

Rationally designed two-photon absorption compounds based on benzoxazole derivatives: structure–property relationships and bio-imaging applications

A new series of benzoxazole-based two-photon absorption (2PA) chromophores (T1-5) were synthesized and fully characterized. Among them, T1-3 are linear donor (D)-π-acceptor (A) type fluorophores with various electron-donating groups, while T4 and T5 are multi-branched compounds stemming from T3. Their photophysical properties have been systematically investigated, and the two-photon absorption properties indicate that the highest 2PA cross-section (σ2PA) is 2702 GM for T5 (in DMF). Structure-property relationships of the chromophores are comprehensively discussed based on their optical properties, crystal structures and density functional theory (DFT) calculations. In addition, a two-photon fluorescence cell imaging experiment demonstrates the potential bio-application of T1-5 with good photostability and low cytotoxicity.

Branched triphenylamine-core compounds: aggregation induced two-photon absorption

Three branched molecules (T1–T3) were synthesized through simple step to realize or enhance two-photon absorption (2PA) in aggregates. Spectra data show that one- and two-branched molecules (T1 and T2) possessed remarkable AIE properties, which came from the formation of J-aggregation because of their partial planarization in an aggregated state. SEM and DLS illustrate that the ordered aggregation and the small particle size had an important influence on fluorescence emission. Open aperture Z-scan experiments show that T1 and T2 possessed excellent 2PA properties in the aggregated state. The largest 2PA cross section was 8314 GM for T2 in aggregates, which was about 13-fold higher than that in pure solution. All the results demonstrate that the compounds could obtain outstanding 2PA performance by rationally adjusting their structure or changing state, which could provide a reference for preparing strong 2PA compounds.

Synthesis, photophysical and electrochemical properties of two novel carbazole-based dye molecules.

Two carbazole-based dye molecules: 3-(6-benzothiazol-2-yl-9H-hexylcarbazole-3-yl)-2-cyano-acylic acid (D3) and 3-[5-(6-benzothiazol-2-yl-9H-hexylcarbazole-3-yl)-thiophen-2-yl]-2-cyan-acylic acid (D4) were synthesized by an approach from carbazole derivate using Vilsmeier-Haack, Suzuki cross-coupling and Knoevenagel reactions. Their physical and electrochemical properties were investigated. D3 and D4 exhibit different optical properties, such as UV absorption, photoluminescence, fluorescence quantum yield and fluorescence lifetime in different solvents. Compared with D3 without a thiophene unit, the maximum absorption wavelength of D4 red-shift obviously and its fluorescence intensity is also enhanced. A shift of the EHOMO and ELUMO is observed for D3 (EHOMO=2.06 V, ELUMO=-1.39 V vs. NHE) and D4 (EHOMO=1.73 V, ELUMO=-1.33 V vs. NHE). D3 and D4 can be used as dyes for dye-sensitized solar cells (DSSCs) with TiO2 nanomaterial because their EHOMO are lower than the conduction band edge of TiO2 [-0.5 V (vs. NHE)] and their ELUMO are higher than the I(3-)/I(-) redox potential [0.42 V (vs. NHE)].

New dyes with enhanced two-photon absorption cross-sections based on the Cd(II) and 4′-(4-[4-(imidazole)styryl]phenyl)-2,2′ : 6′,2″-terpyridine

A series of new cadmium complexes (dyes 1–5) were obtained by assembly of the donor–bridge–acceptor (D–π–A)-type ligand (L: 4′-(4-[4-(imidazole)styryl]phenyl) 2,2′ : 6′,2″-terpyridine) with CdX2 (X=Cl, Br, I, NCS, ClO4), in which dye 3 was characterized by single crystal X-ray diffraction. Various weak interactions, including hydrogen bonds (C–H⋯N, C–H⋯X) and π–π interactions, played significant roles in the final topological structures. Linear and non-linear optical properties of ligand and the complexes were investigated. The two-photon absorption cross-section of these complexes are larger than that of ligand with maximum values of 577 GM (dye 1), 242 GM (dye 2), 171 GM (dye 3), 326 GM (dye 4), and 215 GM (dye 5) in N,N-dimethylformamide.

Application and recognition behaviors of TPA-cored probes with subtle structural change.

Two new triphenylamine-cored probes (L1, L2) with different receptor units have been synthesized and fully characterized by IR, NMR and MS spectra. Their photophysical properties have been investigated in detail. The recognition abilities of two probes were evaluated by a series of metal ions, which showed that L1 could recognize Cu(2+) over other metal ions. L2 could respond to Cu(2+), Hg(2+) in a short time, which interferes with a little each other. The Jobs plot and (1)H NMR titration of L1 with Cu(2+) and L2 with Cu(2+) (Hg(2+)) in CD3CN verified the coordination mode of complexes L1-Cu(2+), L2-Cu(2+) and L2-Hg(2+), respectively. The limit of detection of L2 for Cu(2+) was lower than that of L1 towards Cu(2+). The results demonstrated that the receptor units in the probes had remarkable effect on recognizing metal ions. Meanwhile, L1 and L2 showed potential application in bio-imaging after mixing with Cu(2+).

A lipid droplet-targeted fluorescence probe for visualizing exogenous copper (II) based on LLCT and LMCT

A simple and sensitive probe, pyridine-based Schiff base (PBSB), is prepared based on the previous studies, which shows a rapid response to copper (II) through a fluorescence enhancement process. On association with copper (II), PBSB immediately presents a large red-shift (130 nm) in emission spectrum simultaneously accompanying with increasing emission intensity. The mechanism and binding sites of PBSB detecting copper (II) have been established by theoretical calculations and 1HNMR study, respectively. More importantly, in the complex biological system, PBSB having an excellent membrane permeability and a great photostability can visualize copper (II) in lipid droplet by bio-imaging, which display so great promising advantages in the issues causing by disorder of copper ions that could be convenient for prevention and control problems with human health and complex bio-system.

Boron-Doped Graphene/ZnO Nanoflower Heterojunction Composite with Superior Photocatalytic Activity

The boron-doped graphene (BG) is synthesized successfully by one pot reduce-doping of graphene oxide (GO) with borane tetrahydrofuran (BH3·THF) and the novel BG/ZnO p–n heterojunction composite between p-type BG and n-type ZnO is obtained via a simple hydrothermal method. The samples are characterized by scanning electron microscopy, the Raman spectroscopy and the UV–Vis diffuse spectroscopy. The results confirm the formation of p–n junction between BG and ZnO. The photodegradation of MB demonstrate that the BG/ZnO composite has superior photocatalytic activity under UV–Vis or visible irradiation. The photocatalytic activity k value of BG/ZnO p–n heterojunction composite is 3.1 and 4.5 times as that of r-GO/ZnO and pure ZnO under white light and is 1.8 and 3.9 times under visible light, respectively. The superior photocatalytic activity of the BG/ZnO composite is ascribed to the formation of p–n heterojunction. The p–n heterojunction can promote the separation of electron/hole pairs and inhibit the recombination of electrons in conduction band and holes in valence band by transferring holes from the valence band of n-type ZnO to the valence band of p-type BG.