Construction of Well-Defined Redox-Responsive CO2 -Based Polycarbonates: Combination of Immortal Copolymerization and Prereaction Approach.

Due to the axial group initiation in traditional (salen)CoX/quaternary ammonium catalyst system, it is difficult to construct single active center propagating polycarbonates for copolymerization of CO2 /epoxides. Here a redox-responsive poly(vinyl cyclohexene carbonate) (PVCHC) with detachable disulfide-bond backbone is synthesized in a controllable manner using (salen)CoTFA/[bis(triphenylphosphine)iminium, [PPN]TFA binary catalyst, where the axial group initiation is depressed by judiciously choosing 3,3'-dithiodipropionic acid as starter. While for those comonomers failing to obtain polycarbonate with unimodal gel permeation chromatography (GPC) curve, a versatile method is developed by combination of immortal copolymerization and prereaction approach, and functional aliphatic polycarbonates having well-defined architecture and narrow polydispersity can be prepared. The resulting PVCHC can be further functionalized with alkenes by versatile cross-metathesis reaction to tune the physicochemical properties. The combination of immortal polymerization and prereaction approach creates a powerful platform for controllable synthesis of functional CO2 -based polycarbonates.

Novel conjugated polymers based on dithieno[3,2-b:6,7-b]carbazole for solution processed thin-film transistors.

Two conjugated polymers (CPs) P-tCzC12 and P-tCzC16 comprising alternating dithieno[3,2-b:6,7-b]carbazole and 4,4'-dihexadecyl-2,2'-bithiophene units have been designed and synthesized. Upon thermal annealing, they can form ordered thin films in which the polymer backbones dominantly adopted an edge-on orientation respective to the substrate with a lamellar spacing of ≈24 Å and a π-stacking distance of ≈3.7 Å. Organic thin-film transistors (OTFTs) were fabricated by solution casting. A hole mobility of 0.39 cm(2) V(-1) s(-1) has been demonstrated with P-tCzC16. This value is the highest among the CPs containing heteroacenes larger than 4 rings.

The first soluble conjugated poly(2,6-anthrylene): synthesis and properties.

The first soluble conjugated poly(2,6-anthrylene) with 9,10-diphenyl-anthracene as the repeating unit is reported; photophysical studies reveal that this polymer represents a novel well-conjugated system.

Modification of porous PLGA microspheres by poly-l-lysine for use as tissue engineering scaffolds.

Due to their good biocompatibility, biodegradability and special shapes, porous poly(lactic-co-glycolic acid) (PLGA) microspheres show a wide application in the field of tissue engineering. Herein we demonstrate a simple and low-cost method for modifying porous PLGA microspheres with poly-l-lysine (PLL) to promote cell growth on the microspheres. Porous PLGA microspheres were first treated by sodium hydroxide (NaOH) solution to introduce carboxyl groups on their surface. Then, the hydrolyzed microspheres (PLGA-H) were immerged in PLL solution to yield PLL-impregnated microspheres (PLGA-PLL). Cell experiments showed that although the cytotoxicity of microspheres was slightly increased after PLL modification, their cell viability was still higher than 85%. Compared with PLGA and PLGA-H microspheres, PLGA-PLL microspheres were more favorable for MG63 cell to attach and proliferate due to their increased initial cell attachment numbers and enhanced cell-matrix interactions. This new modification method of porous PLGA microspheres proposes a route toward efficient repair of tissue defects at reduced risk and cost level.

Conductive super-hydrophobic surfaces of polyaniline modified porous anodic alumina membranes.

A conductive polymer polyaniline (PANI) was employed to achieve surfaces of both super-hydrophobic and conductive on NaOH etched porous anodic alumina (PAA) membranes. The surfaces exhibit micro- and nanostructures. In the PANI modified PAA membrane, PANI is mainly emeraldine. After the membrane was immersed in HCl, the content of the protonated nitrogen increased, which increased the conductivity.

Spiro-linked hyperbranched architecture in electrophosphorescent conjugated polymers for tailoring triplet energy back transfer.

A spiro-linked hyperbranched architecture has been incorporated into electrophosphorescent conjugated polymers for the first time, aiming at simultaneously tailoring the intra- and intermolecular triplet energy back transfer from the phosphorescent guest to the conjugated polymer host. Based on a prototype with this unique structure, slower decay of triplet excitons, and 5-8 fold enhancement of device efficiencies are obtained compared with the conventional blending counterpart.

From tunneling to hopping: a comprehensive investigation of charge transport mechanism in molecular junctions based on oligo(p-phenylene ethynylene)s.

The charge transport mechanism of oligo(p-phenylene ethynylene)s with lengths ranging from 0.98 to 5.11 nm was investigated using modified scanning tunneling microscopy break junction and conducting probe atomic force microscopy methods. The methods were based on observing the length dependence of molecular resistance at single molecule level and the current-voltage characteristics in a wide length distribution. An intrinsic transition from tunneling to hopping charge transport mechanism was observed near 2.75 nm. A new transitional zone was observed in the long length molecular wires compared to short ones. This was not a simple transition between direct tunneling and field emission, which may provide new insights into transport mechanism investigations. Theoretical calculations provided an essential explanation for these phenomena in terms of molecular electronic structures.

Probing charge transport of ruthenium-complex-based molecular wires at the single-molecule level.

A ruthenium(II) bis(sigma-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 pi-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.