Probing Charge Transport of Ruthenium-Complex-Based Molecular Wires at the Single-Molecule Level

A ruthenium(II) bis(σ-arylacetylide)-complex-based molecular wire functionalized with thiolacetyl alligator clips at both ends (OPERu) was used to fabricate gold substrate−molecular wire−conductive tip junctions. To elucidate the ruthenium-complex-enhanced charge transport, we conducted a single-molecule level investigation using the technique-combination method, where electronic decay constant, single-molecular conductance, and barrier height were obtained by scanning tunneling microscopy (STM) apparent height measurements, STM break junction measurements, and conductive probe-atomic force microscopy (CP-AFM) measurements, respectively. A quantitative comparison of OPERu with the well-studied π-conjugated molecular wire oligo(1,4-phenylene ethynylene) (OPE) indicated that the lower electronic decay constant as well as the higher conductance of OPERu resulted from its lower band gap between the highest occupied molecular orbital (HOMO) and the gold Fermi level. The small offset of 0.25 eV was expected to be beneficial for the long-range charge transport of molecular wires. Moreover, the observed cross-platform agreement proved that this technique-combination method could serve as a benchmark for the detailed description of charge transport through molecular wires

Syntheses, Characterization, and Ethylene Polymerization of Half-Sandwich Zirconium Complexes with Tridentate Imino−Quinolinol Ligands

A series of half-sandwich zirconium complexes with imino-quinolinol ligands have been synthesized and characterized. The catalytic behaviors of these complexes toward ethylene polymerization were investigated in the presence of methylaluminoxane (MAO) as a cocatalyst. The catalytic behaviors were highly affected by the substituent in both cyclopentadienyl and imino−quinolinol ligands. The Cp analogue complexes CpZr[ONNR]Cl2 (1a−e) exhibited high activities up to 1.34 × 107 g of PE (mol of Zr)−1 h−1, whereas the Cp* analogue complexes Cp*Zr[ONNR]Cl2 (2a−e) also showed moderate activities for ethylene polymerization

Syntheses, Characterization, and Ethylene Polymerization of Half-Sandwich Zirconium Complexes with Tridentate Imino−Quinolinol Ligands

A series of half-sandwich zirconium complexes with imino-quinolinol ligands have been synthesized and characterized. The catalytic behaviors of these complexes toward ethylene polymerization were investigated in the presence of methylaluminoxane (MAO) as a cocatalyst. The catalytic behaviors were highly affected by the substituent in both cyclopentadienyl and imino−quinolinol ligands. The Cp analogue complexes CpZr[ONNR]Cl2 (1a−e) exhibited high activities up to 1.34 × 107 g of PE (mol of Zr)−1 h−1, whereas the Cp* analogue complexes Cp*Zr[ONNR]Cl2 (2a−e) also showed moderate activities for ethylene polymerization

Reversible Sol–Gel Transition of Oligo(<i>p</i>‑phenylenevinylene)s by π–π Stacking and Dissociation

Methyl sulfide terminated <i>trans</i>-oligo­(<i>p</i>-phenylenevinylene) derivatives (<b>OPV</b><i><b>n</b></i>, <i><b>n</b></i> is the number of phenyl rings) were synthesized, and reversible sol–gel transition was observed in a variety of organic solvents. Investigations with UV–vis, fluorescence, and ¹H NMR spectroscopy revealed that aromatic π–π stacking and van der Waals forces were important in the formation of the gels, with the former being the main driving force for sol–gel transition. The π-conjugation length showed a key influence on self-assembly and gelation property: the gel-to-sol transition temperature (<i>T</i>_gel) increased with π-conjugation length. The gels of <b>OPV4–7</b> can self-assemble into one-dimensional fibers with different sizes and shapes, depending on their π-conjugation length. On the basis of X-ray diffraction measurements and spectroscopic data, a self-assembly model was proposed. Our observation may be useful for designing functional π-gelators based on π–π stacking

Length Dependence of Electron Conduction for Oligo(1,4-phenylene ethynylene)s: A Conductive Probe-Atomic Force Microscopy Investigation

The dependence of electron conduction of oligo(1,4-phenylene ethynylene)s (OPEs) on length, terminal group, and main chain structure was examined by conductive probe-atomic force microscopy (CP-AFM) via a metal substrate−molecular wire monolayer−conductive probe junction. The electron transport in the molecular junction was a highest occupied molecule orbital (HOMO)-mediated process following a coherent, non-resonant tunneling mechanism represented by the Simmons equation. The length of OPEs was the dominant factor in determining electron conduction across the metal−molecular wires−metal junction, where the resistances of OPEs scaled exponentially against molecular length in a structure-dependent attenuation factor of 0.21 ± 0.01 Å-1

Trivalent Titanium Salen Complex: Thermally Robust and Highly Active Catalyst for Copolymerization of CO₂ and Cyclohexene Oxide

A trivalent titanium complex combining salen ligand (salen-H₂<i>N,N</i>-bis­(3,5-di-<i>tert</i>-butylsalicylidene)-1,2-benzenediamine) was synthesized as catalyst for copolymerization of CO₂ and cyclohexene (CHO). In combination with onium salt [PPN]­Cl, (Salen)­Ti­(III)Cl showed impressive activity and selectivity, yielding completely alternating copolymer without the formation of cyclohexene carbonate (CHC), with turnover frequency (TOF) of 557 h^–1 at 120 °C, which was more than 10 times higher than that of our previously reported (Salalen)­Ti­(IV)­Cl, and close to the Cr counterparts. In addition to the biocompatibility of Ti, thermally robust character resulting from the reducibility of trivalent Ti was industrially desirable

“Turn-On” Conjugated Polymer Fluorescent Chemosensor for Fluoride Ion

“Turn-On” Conjugated Polymer Fluorescent Chemosensor for Fluoride Io

Enhancing Molecular Conductance of Oligo(<i>p</i>‑phenylene ethynylene)s by Incorporating Ferrocene into Their Backbones

Designing and preparing the molecular wires with good charge transport performance is of crucial importance to the development of molecular electronics. By incorporating ferrocene into molecular backbones, we successfully enhanced the molecular conductance of OPEs in both tunneling and hopping conduction regimes. Furthermore, we found that the increase degree of molecular conductance in the hopping regime is much more than that in the tunneling regime. Via this approach, the molecular conductance of a long molecule exceeds the molecular conductance of a short one at room temperature. A theoretical calculation provided a possible and preliminary explanation for these novel phenomena in terms of molecular electronic structures. The current work opens the opportunity for designing excellent charge transport performance molecules. An increasing number of new types of molecular wires with this unusual phenomenon are expected to be discovered in the future

Highly Selective Fluorescent Chemosensor for Silver(I) Ion Based on Amplified Fluorescence Quenching of Conjugated Polyquinoline

Highly Selective Fluorescent Chemosensor for Silver(I) Ion Based on Amplified Fluorescence Quenching of Conjugated Polyquinolin

Poly(phenylene sulfide−tetraaniline): The Soluble Conducting Polyaniline Analogue with Well-Defined Structures

A novel conducting polymer poly(phenylene sulfide−tetraaniline) (PPSTEA), with tetraaniline (TA) and phenylene sulfide (PS) segments in its repeat unit, has been synthesized through an acid-induced polycondensation reaction of 4-methylsulfinylphenyl-capped tetraaniline. The new polymer, which represents the first soluble conducting polyaniline analogue with well-defined structure, has high molecular weight, good solubility in common solvents, and good film-forming properties. Its electrical property is analogous to polyaniline. The conductivity of preliminarily protonic-doping PPSTEA is up to 100 S/cm. This synthetic strategy appears to be general for developing novel well-defined polyaniline analogue containing much longer fixed conjugation length