Zhu-Guo Xu

A Facile Phosphine-Free Method for Synthesizing PbSe Nanocrystals with Strong Optical Limiting Effects

PbSe semiconductor nanocrystals (NCs) have attracted ever-growing interest owing to both their fundamental physics and potential applications in a diverse range of fields such as optoelectronic devices and nonlinear optics. The current fabrication strategy for colloidal PbSe NCs, however, frequently involves acutely toxic reagents and tedious reaction procedures, and is plagued by products with poorly controlled size and morphology. Herein, we report a facile, low-cost, and phosphine-free method for synthesizing PbSe NCs, which provides highly uniform NCs with tunable mid-IR absorption, and they are promising for bio-related applications. These high quality NCs were obtained by the reaction of elemental Se and PbCl2 in oleylamine as both the ligand and reaction medium. The high flexibility and reproducibility of the method reported in this study allows us to synthesize monodispersed PbSe NCs with well-controlled size and morphology. In addition, these products show strong optical limiting effects, and thus hold potential for developing nonlinear optical devices.

Improved synthesis of PbSxSe1−x ternary alloy nanocrystals and their nonlinear optical properties

We report a facile and low-cost phosphine-free method for synthesizing spherical PbSxSe1−x NCs. The alternative routes to the existing methodologies allow us to synthesize monodisperse PbSxSe1−x NCs with better-controlled size and morphology than those previously reported. In addition, their optical limiting effects are reported.

Conformation-Controlled Electron Transport in Single-Molecule Junctions Containing Oligo(phenylene ethynylene) Derivatives

Understanding the relationships between the molecular structure and electronic transport characteristics of single-molecule junctions is of fundamental and technological importance for future molecular electronics. Herein, we report a combined experimental and theoretical study on the single-molecule conductance of a series of oligo(phenylene ethynylene) (OPE) molecular wires, which consist of two phenyl-ethynyl-phenyl π units with different dihedral angles. The molecular conductance was studied by scanning tunneling microscopy (STM)-based break-junction techniques under different conditions, including variable temperature and bias potential, which suggested that a coherent tunneling mechanism takes place in the OPE molecular wires with a length of 2.5 nm. The conductance of OPE molecular junctions are strongly affected by the coupling strength between the two π systems, which can be tuned by controlling their intramolecular conformation. A cos(2)θ dependence was revealed between the molecular conductance and dihedral angles between the two conjugated units. Theoretical investigations on the basis of density functional theory and nonequilibrium Greens functions (NEGF) gave consistent results with the experimental observations and provided insights into the conformation-dominated molecular conductance.

Dimethyl 2,5-bis­(5-hexyl­thio­phen-2-yl)benzene-1,4-dioate

In the title compound, C30H38O4S2, the centroid of the benzene ring lies on a center of inversion. The thiophene ring is aligned at 49.8 (1)° with respect to the benzene ring. The alkyl chain adopts an extended zigzag conformation.

2-(Naphthalen-2-yl)azulene.

In the title compound, C20H14, a naphthalene ring system is linked at the 2-position to the 2-C atom of the five-membered ring of an azulene unit. The compound crystallizes with two reasonably similar molecules in the asymmetric unit. Neither molecule is perfectly planar: the r.m.s. deviations from the best fit planes through all non-H atoms are 0.092 and 0.091 Å for the two molecules. The dihedral angle between the molecular planes is 49.60 (4)°. The naphthalene and azulene ring systems are inclined at dihedral angles of 6.54 (12) and 5.68 (12)° in the two molecules. The crystal structure exhibits two sets of parallel layers, a typical edge-to-face herringbone packing arrangement. The structure is stabilized by an extensive series of weak C—H⋯π interactions.