Dongling Wu

Interaction between Nitrogen and Sulfur in Co-Doped Graphene and Synergetic Effect in Supercapacitor

The co-doping of graphene with nitrogen and sulfur was investigated aiming at understanding their interactions with the presence of oxygen in graphene. The co-doped graphene (NS-G) was synthesized via a one-pot hydrothermal route using graphene oxide as starting material and L-cysteine, an amino acid containing both N and S, as the doping agent. The obtained NS-G with a three-dimensional hierarchical structure containing both macropores and mesopores exhibited excellent mechanical stabilities under both wet and dry conditions. As compared to N or S singly doped graphene, the co-doped sample contains significantly higher concentrations of N and S species especially pyrollic N groups. The co-doped sample considerably outperformed the singly doped samples when used as free-standing electrode in supercapacitors due to enhanced pseudocapacitance. The simultaneous incorporation of S and N species with the presence of oxygen significantly modified the surface chemistry of carbon leading to considerably higher doping levels, although directly bonding between N and S is neither likely nor detected. Hence, the synergetic effect between N and S occurred through carbon atoms in neighboring hexagonal rings in a graphene sheet.

Hydrothermal synthesis of nitrogen-doped graphene hydrogels using amino acids with different acidities as doping agents

A one-pot hydrothermal route was developed for the preparation of nitrogen-doped graphene (NG) hydrogels using graphene oxide (GO) as a raw material and nine amino acids with different acidities (acidic, neutral and basic) as doping agents. The morphology, structure and composition of the prepared NG using three amino acids (DL-aspartic acid, acidic; L-glycine, neutral; L-arginine, basic) were characterized by SEM, nitrogen physisorption, Raman and XPS spectroscopy. Acidic amino acids yielded NG with a cross-linked 3D network with a large specific surface area of 367.1 m2 g−1, while NG arising from the use of basic amino acids showed a tightly stacked structure with a much smaller surface area of 10.5 m2 g−1. The charged amino acids, and the ensuing electrostatic interactions between the amino acid and GO, affect the morphology of NG, and ultimately affect its electrochemical performance. The samples prepared using acidic amino acids, with the lowest surface N content (1.0%) but the largest surface area, displayed high specific capacitance of 246 F g−1 at 3 A g−1. The microstructure, surface area and effective nitrogen content, mainly the pyridinic nitrogen group related to pseudocapacitance, play important roles in the capacitive performance of the NG samples.

Study of fluorescence properties of several 4-acyl pyrazolone derivatives and their Zn (II) complexes.

Fluorescence properties of four 4-acyl pyrazolone derivatives (H(2)L(1)=N-(1,3-diphenyl-4-propylene-5-pyrazolone)-salicylidene hydrazone (1), H(2)L(2)=N-(1,3-diphenyl-4-ethylene-5-pyrazolone)-salicylidene hydrazone (2), H(2)L(3)=N-(1,3-diphenyl-4-benzylidene-5-pyrazolone)-salicylidene hydrazone (3), H(2)L(4)=N-(1,3-diphenyl-4-phenylethylene-5-pyrazolone)-salicylidene hydrazone (4), and their Zn (II) complexes: (Zn(H(2)L(1))(2) (5), Zn(H(2)L(2))(2).3CH(3)OH (6), Zn(H(2)L(3))(2).2CH(3)OH (7), and Zn(4)(H(2)L(4))(4) (8)) were studied at room temperature. It was revealed that these compounds show different fluorescence properties both in the solid state and in solution. Density functional theory (DFT) calculations on ligands 1-4 were also performed to further understand their emission properties. The calculation results indicate that the energy gaps between the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) of these ligands are in the following order 1>2>3, which is consistent with the redshift of the emission spectra.

Photo-switch and INHIBIT logic gate based on two pyrazolone thiosemicarbazone derivatives

Two novel compounds containing a pyrazolone-ring unit, i.e.1-phenyl-3-methyl-4-(2-fluorobenzal)-5-hydroxypyrazole 4-methylthiosemicarbazone and 1-phenyl-3-methyl-4-(2-fluorobenzal)-5-hydroxypyrazole 4-ethylthiosemicarbazone, have been synthesized and characterized by MS, IR, 1H NMR spectra and X-ray single crystal diffraction. In solid state, they exhibit reversible photochromic properties under UV light irradiation and heating. Based on the crystal structure, solid IR spectra and theoretical calculation, the photochromic mechanism of the intra- and intermolecular double-proton transfer from the enol form to the keto form is proposed. In solution, stimulated by three chemical inputs (H+, OH− and Zn2+), they undergo the deprotonation–protonation and complexation reactions. Based on an absorption band at 355 nm as the output signal, an INHIBIT logic gate combining a NOT and an AND gate has been obtained.

Photochromism and mechanism of pyrazolones in crystals: structural variations directly observed by X-ray diffraction

Structural changes of photochromic pyrazolones were first verified by an X-ray crystallographic method directly. A tautomeric transformation between enol and keto form isomers occurs, accompanied by proton transfer during the photochromic processes.

Synthesis, photoisomerization properties and thermal bleaching kinetics of pyrazolones containing 3-cyanobenzal.

Through the design of molecules and the modification of structures, ten novel pyrazolone derivatives containing 3-cyanobenzal have been synthesized. They are 1-phenyl-3-methyl-4-(3-cyanobenzal)-5-hydroxypyrazole thiosemicarbazone (1)/4-methyl-3-thiosemicarbazone (2)/4-ethyl-3-thiosemicarbazone (3)/4-phenyl-3-thiosemicarbazone (4)/4-phenylsemicarbazone (5) and 1,3-diphenyl-4-(3-cyanobenzal)-5-hydroxypyrazole thiosemicarbazone (6)/4-methyl-3-thiosemicarbazone (7)/4-ethyl-3-thiosemicarbazone (8)/4-phenyl-3-thiosemicarbazone (9)/4-phenylsemicarbazone (10), in which seven compounds (1, 2, 3, 6, 7, 8 and 10) have photoisomerization behaviors. Their structures, photoisomerization properties, and first-order kinetics were investigated. The results show that the compounds 2, 3, 7 and 8 exhibit irreversible photoisomerization behaviors, the other three compounds have reversible photoisomerization behaviors under 365nm light irradiation and heat. But only 1,3-diphenyl-4-(3-cyanobenzal)-5-hydroxypyrazole 4-phenylsemicarbazone (10) exhibits good photochromic properties and fatigue resistance. Moreover, effects of various temperatures on the thermal bleaching reaction for 10 and substituent groups on the photochromic phenomenon are discussed.

Synthesis, photochromic properties and thermal bleaching kinetics of pyrazolone phenylsemicarbazones containing a thiophene ring

Five novel pyrazolone derivatives containing a thiophene ring, 1-phenyl-3-(2-thiophenyl)-4-(3-bromobenzal)-5-hydroxypyrazole phenylsemicarbazone (1)/1-phenyl-3-(2-thiophenyl)-4-(3-chlorobenzal)-5-hydroxypyrazole phenylsemicarbazone (2)/1-phenyl-3-(2-thiophenyl)-4-benzal-5-hydroxypyrazole phenylsemicarbazone (3)/1-phenyl-3-(2-thiophenyl)-4-(4-bromobenzal)-5-hydroxypyrazole phenylsemicarbazone (4)/1-phenyl-3-(2-thiophenyl)-4-(4-chlorobenzal)-5-hydroxypyrazole phenylsemicarbazone (5), were synthesized. Among them, only two compounds (1 and 2) have excellent photochromic properties. Their structures, photochromic properties, thermal bleaching kinetics and the activation energies of the thermal bleaching process were investigated. The results show that the two compounds exhibit reversible enol–keto isomerization reaction under 365 nm light irradiation and heat, and high fatigue resistance.

Fluorescence modulation of a pyrazolone dye in the solid state based on energy transfer

A new pyrazolone dye was synthesized and its fluorescence modulation was achieved based on energy transfer. The prepared pyrazolone dye was combined with a photochromic pyrazolone to obtain a fluorescence photoswitching material (FPM), which exhibits stable and reversible fluorescence photoswitching properties in the solid state. Upon characterization of the samples through 1H NMR, XRD, FT-IR, UV and fluorescence spectra, it was found that the photochromic pyrazolone and the pyrazolone dye integrally retained their inherent properties in the FPM. An investigation of the FPM revealed that the photoswitching response depended on the fluorescence dye species, the content of the fluorescence dye and the synthetic route of the FPM. The photoswitching mechanism of the FPM was studied in detail using FT-IR, UV and fluorescence spectroscopy. The results show that the photochromism of the photochromic pyrazolone plays an important role in the efficient energy transfer from the pyrazolone dye to the keto-form of the photochromic pyrazolone. The emission wavelength of the pyrazolone dye hardly induces a photochemical reaction of the photochromic pyrazolone in the FPM, which has the potential to be used as a non-destructive fluorescence readout of optical information. This study presents a simple and efficient alternative to covalent systems to obtain FPMs, and it may be applied in photoelectronic devices.

THEORETICAL STUDIES ON THE CONFORMATION AND COORDINATION OF N-(1-PHENYL-3-METHYL-4-PROPENYLIDENE-5-PYRAZOLONE)-SALICYLIDENE

Density functional theory (DFT) calculation has been carried out to investigate the isomers of N-(1-phenyl-3-methyl-4-propenylidene-5-pyrazolone)-salicylidene. Chemical potential, chemical hardness and global electrophilicity, which are considered as global indices, have been calculated to assess the stability and reactivity of the tautomers. The condensed Fukui function is calculated for predicting the most probable sites for electrophilic attack. Molecular electrostatic potential is calculated to predict the regions for electrophilic attack.