Yupeng Tian

Crystal structure and spectroscopic studies on metal complexes containing ns donor ligands derived from S-benzyldithiocarbazate andp-dimethylaminobenzaldehyde

Abstract A series of neutral bis-ligand Cu II , Ni II , Pd II and Pt II chelates with Schiff base ligands derived from S-benzyldithiocarbazate and p -dimethylaminobenzaldehyde were prepared and characterized. The Schiff base acts as a single, negatively charged bidentate ligand forming stable neutral metal complexes. Magnetic and spectroscopic data suggest a square-planar structure for the Ni II , Pd II and Pt II chelates. Also, ESR spectral and variable-temperature magnetic suspectibility data support the square-planar structure of Cu II chelate. Cyclic voltammograms show that the coordination ability of the metal is the main factor influencing the redox potential of the Schiff base ligand in the complexes. Single cyrstal X-ray diffraction analysis of the nickel(II) chelate established that the Schiff base has lost a proton from its tautometric thiol form and coordinated to Ni II via the mercapto sulphur and β-nitrogen. The geometry around Ni II is square-planar with two equivalent Ni N and Ni S bonds; the two dimethylaminophenyl rings and the coordinated plane are almost in one plane forming an electronic delocalization system.

Exfoliation of Hexagonal Boron Nitride by Molten Hydroxides

Hexagonal boron nitride (h-BN) nanosheets are prepared by a novel and effective method, in which sodium hydroxide and potassium hydroxide molten salts are used to exfoliate h-BN to obtain nanosheets. BN nanoscrolls are also obtained. The as-prepared products can be readily dispersed in a wide range of solvents, including water and ethanol, and form stable dispersions.

A highly selective colorimetric chemosensor for detecting the respective amounts of iron(II) and iron(III) ions in water

A novel colorimetric chemosensor containing terpyridine was synthesized. It showed high selectivity and sensitivity for Fe(II) and Fe(III) ions in neutral aqueous solution in the presence of other metal ions such as Cd2+, Cr3+, Zn2+, Co2+, Ni2+, Cu2+, Pb2+, Na+, Ca2+, Mg2+, K+ and Ag+. Upon the addition of Fe2+ or Fe3+, the sensor displayed a unique new peak around 567 nm in its absorption spectra, and the color of the solution changed from light yellow to light magenta. In particular, the respective amounts of Fe(II) and Fe(III) ions in the solution can be detected using the light-absorption ratio variation approach (LARVA).

Enhanced electrochemiluminescence of CdSe quantum dots composited with graphene oxide and chitosan for sensitive sensor.

A novel strategy for the enhancement of electrochemiluminescence (ECL) was developed by combining CdSe quantum dots (QDs) with graphene oxide-chitosan (GO-CHIT). The ECL sensor fabricated with CdSe QDs/GO-CHIT composite exhibited high ECL intensity, good biocompatibility and long-term stability, and was used to detect of cytochrome C (Cyt C). The results show that the ECL sensor has high sensitivity for Cyt C with the linear range from 4.0 to 324 μM and the detection limit of 1.5 μM. Furthermore, the ECL sensor can selectively sense Cyt C from glucose and bovine serum albumin (BSA).

Aggregation-Induced Fluorescence Behavior of Triphenylamine-Based Schiff Bases: The Combined Effect of Multiple Forces

Eight triphenylamine (TPA)-based Schiff bases that exhibit different aggregation-induced emission (AIE) or aggregation-caused quenching (ACQ) behavior in tetrahydrofuran (THF)/water mixtures have been synthesized and characterized. The photophysical properties in solution, aqueous suspension, film, and the crystalline state along with their relationships were comparatively investigated. The single-crystal structures of 1-8 indicate that compact π···π stacking or excimers induce fluorescence quenching of 1, 2, 5, and 7. However, the existence of J aggregates or multiple intra- and intermolecular interactions restrict the intramolecular vibration and rotation, enabling compounds 3, 4, 6, and 8 to exhibit good AIE character. The size and growth process of particles with different water fractions were studied using scanning electron microscopy, which demonstrated that smaller uniformly dispersed nanoparticles in the THF/water mixtures favor fluorescence emission. The above results suggest that the combined effects of multiple forces caused by structural variation have a great influence on their molecular packing, electronic structure, and aggregation-induced fluorescence properties. In addition, piezofluorochromic experiments verified the potential applications of 4 and 6.

Enhanced Singlet Oxygen Generation in Oxidized Graphitic Carbon Nitride for Organic Synthesis.

Experimental data reveal that the incorporation of carbonyl groups into polymer matrix can significantly enhance singlet oxygen ((1) O2 ) generation and suppress production of other reactive oxygen species. Excitonic processes investigated by phosphorescence spectroscopy reveal enhanced triplet-exciton generation in the modified g-C3 N4 , which facilitate (1) O2 generation through an energy transfer process. Benefiting from this, the modified g-C3 N4 shows excellent conversion and selectivity in organic synthesis.

Facile synthesis and systematic investigations of a series of novel bent-shaped two-photon absorption chromophores based on pyrimidine.

The synthesis, structure, and single- and two-photon spectroscopic properties of a series of pyrimidine-based (bent-shaped) molecules are reported. All these stable heterocyclic compounds are fully characterized, and exhibit intense single- and two-photon excited fluorescence (SPEF and TPEF) over a wide spectral range from blue to red, with the spectral peak position of the SPEF being basically the same as that of the TPEF. The well-conjugated pi-systems, observed from the crystal structure, indicate the charge transfer feature of the ground state. Meanwhile, the theoretical and experimental studies indicate that the charge transfer from donor to acceptor is greatly enhanced in the excited states and the different substituted donor groups on the pyrimidine have a large effect on the optical and electrochemical properties. Based on typical structure data and comprehensive spectral data, the following structure-property relationships can be determined: for such bent-shaped chromophores, the absorption and the fluorescence wavelength maximum of the SPEF and TPEF, and two-photon absorption cross sections show a similar trend with increasing electron-donating strength of the corresponding terminal group and the number of branches, while the average bond lengths of the pi-linkage and HOMO-LUMO energy levels show an inverse trend. Experimental data and theoretical calculation provide a coherent picture. With these findings, bent-shaped quadrupolar chromophores combining peak TPA cross sections (up to 2280 GM), broad TPA bands throughout the whole 700-900 nm range, and high fluorescence quantum yields could, thus, be obtained. Such compounds are of particular interest for TPEF microscopy, as well as optical data storage in the visible and NIR regions. A data recording experiment proved the potential application of these materials.

Substituent group variations directing the molecular packing, electronic structure, and aggregation-induced emission property of isophorone derivatives.

A series of new isophorone derivatives (1-5), incorporating the heterocyclic ring or aza-crown-ether group, with large Stokes shifts (>140 nm), have been synthesized and characterized. 1-4 display aggregation-induced emission behaviors, while dye 5 is highly emissive in solution but quenched in the solid state. It was found that the tuning of emission color of the isophorone-based compounds in the solid state could be conveniently accomplished by changing the terminal substituent group. The photophysical properties in solution, aqueous suspension, and crystalline state, along with their relationships, are comparatively investigated. Crystallographic data of 1-4 indicate that the existence of multiple intermolecular hydrogen bonding interactions between the adjacent molecules restricts the intramolecular vibration and rotation and enables compounds 1-4 to emit intensely in the solid state. The size and growth processes of particles with different water fractions were studied using a scanning electron microscope, indicating that smaller globular nanoparticles in aqueous suspension are in favor of fluorescence emissions. The above results suggest that substituent groups have a great influence on their molecular packing, electronic structure, and aggregation-induced emission properties. In addition, fluorescence cell imaging experiment proved the potential application of 5.

Synthesis, structure and properties of a new two-photon photopolymerization initiator

A new two-photon free-radical photopolymerization initiator, (E,E)-4-{2-[p′-(N,N-di-n-butylamino)stilben-p-yl]vinyl}pyridine (abbreviated to DBASVP), has been synthesized. Quantum chemistry calculations showed that the new initiator possesses a large delocalized π electron system, a large change in dipole moment on transition to the excited state and a large transition moment. The calculated two-photon absorption cross-section is as high as 881.34 × 10−50 cm4 s photon−1. The single-photon and two-photon absorption and fluorescence properties in various solvents have been investigated carefully. The new initiator exhibits outstanding solvent-sensitivity, which experimentally interprets the excellent electron delocalized properties of the molecule. A microstructure has been fabricated under irradiation at 800 nm using a 200 fs, 76 MHz Ti:sapphire femtosecond laser.

Investigations and facile synthesis of a series of novel multi-functional two-photon absorption materials

Six centrosymmetric D–(π–A)3 structural triphenylamine derivatives that can be used as two-photon photopolymerization and optical data storage chromophores, tris[4-(4-pyridylethenyl)phenyl]amine (1), tris[4-(2-pyridylethenyl)phenyl]amine (2), tris(4-cyanoethenylphenyl)amine (3), tris[4-butylacrylatephenyl]amine (4), tris[4-methylacrylatephenyl]amine (5) and tris[4-acrylicethenylphenyl]amine (6), have been successfully synthesized via a triple palladium-catalyzed Heck coupling reaction, and the novel chromophores were fully characterized by elemental analysis, IR, 1H-NMR and ESIMS. The structure for 3 was determined by single crystal X-ray diffraction study. One- and two-photon absorption and fluorescence in various solvents were experimentally investigated. Two-photon initiated polymerization microfabrication and optical data recording experiments were carried out under 780 nm laser radiation, and the possible polymerization mechanism is discussed based on theoretical calculations. All the six chromophores have relatively large two-photon absorption cross-sections, and exhibit optical memory and highly efficient two-photon initiated polymerization abilities.