Ting Qi

Novel copolymers incorporating dithieno[3,2-b:2′,3′-d]thiophene moieties for air-stable and high performance organic field-effect transistors

A series of semiconducting copolymers incorporating dithieno[3,2-b:2′,3′-d]thiophene moieties in the polythiophene backbone were synthesized. The resulting four copolymers are found to have large band gap (∼ 2.5 eV) and large ionization potential (−5.1 eV). Organic field-effect transistors were fabricated by spin-coating polymer solutions onto OTS-modified SiO2/Si substrates with top-contact configuration. The best resulting hole mobility afforded was 0.028 cm2V−1 s−1 with an on/off ratio of 2 × 104 and a threshold voltage of about −18.9 V in the saturation regime. Furthermore, all the devices exhibited high environmental stability against oxygen doping and relatively high ambient humidity (∼30%).

Synthesis and properties of fluorene or carbazole-based and dicyanovinyl-capped n-type organic semiconductors

Dicyanovinyl-substituted compounds as electron transport materials are rarely studied, especially oligomers. A new series of fluorene or carbazole-based and dicyanovinyl-capped oligomers consisting of benzene or thiophene segments were synthesized using the Stille coupling reaction and their physical properties were investigated. Optical spectra show that the introduction of electron-accepting groups induces an intramolecular charge transfer, resulting in a shift of the absorption onset toward longer wavelengths. Moreover, the optical spectra of their films show intermolecular interactions, leading to bathochromic shifts with respect to the spectra in solution. Cyclic voltammetry indicates that they have suitable HOMO and LUMO energy levels, and the oligomers containing thiophene segments show lower LUMO levels. The X-ray crystallography of compound FTCN shows that the compound exhibits extended π stacking of the molecules. Thermal analysis reveals that they are thermally stable and no phase transition was observed at low temperatures.

Large-scale and chromatography-free synthesis of an octameric quinoline-based aromatic amide helical foldamer.

The synthesis of helical aromatic oligoamide foldamers derived from 8-amino-2-quinolinecarboxylic acid is described. The precursors are commercially available and products up to and including the octamer are obtained. The procedure covers the synthesis of the monomer, reduction of N-terminal nitro groups into amines, saponification of C-terminal methyl esters to form carboxylic acids, and coupling of amines and acids to form amides via acid chloride activation. Emphasis is given to how these reactions can be scaled up and how purification can be greatly simplified using recrystallization methods, thus providing considerable improvements over previously described procedures. As an illustration of the improvement, 8.4 g of an octamer can now reliably be prepared from a nitro-ester monomer in a matter of 8 (working) weeks without any chromatography.

Highly efficient blue electrophosphorescent devices with a new series of host materials: polyphenylene-dendronized oxadiazole derivatives

A new series of oxadiazole derivatives TPO, PPO, MTPO, MPPO, BTPO, and BPPO have been designed and synthesized in high yields by a convenient synthetic procedure. A single crystal structure of TPO exhibited that this polyphenylene-dendronized material has a sterically crowded structure which efficiently prevents π–π stacking and endows it with good thermal stability. The photophysical properties of the materials show strong emission between 376 and 390 nm in the films. In addition, good reversible reductive waves in the cyclic voltammograms implied that these materials might have good electron transport properties. Blue electrophosphorescent devices fabricated using these materials as the host materials and iridium(III)bis[4,6-di-fluorophenyl-pyridinato-N,C2′]picolinate as the blue phosphorescent dopant emitter show very high efficiencies. A maximum luminance of 4484 cd m−2 and an external quantum efficiency of 6.20% were achieved under ambient conditions.

Asymmetrical Fluorene[2,3-b]benzo[d]thiophene Derivatives: Synthesis, Solid-State Structures, and Application in Solution-Processable Organic Light-Emitting Diodes

A series of novel asymmetrical fused compounds containing the backbone of fluorene[2,3-b]benzo[d]thiophene (FBT) were effectively synthesized and fully characterized. Single-crystal X-ray studies demonstrated that the length of the substituent side chains greatly affects the solid-state packing of the obtained fused compounds. DFT, photophysical, and electrochemical studies all showed that the FBTs have large band gaps, low-lying HOMO energy levels, and therefore good stability toward oxidation. Moreover, the substituents strongly influence the fluorescence properties of the resulting FBT derivatives. The di-n-hexyl compound exhibits intense fluorescence in solution with the highest quantum yield of up to 91 %. Solution-processed green phosphorescent organic light-emitting diodes with the di-n-butyl derivative as the host material exhibited a maximum brightness of 14,185 cd m(-2) and a luminescence efficiency of 12 cd A(-1).

Synthesis and Multibromination of Nanosized Helical Aromatic Amide Foldamers via Segment-Doubling Condensation

The synthesis of very long helical aromatic amide foldamers was thought to be limited by steric hindrance associated with stable folded conformations. This difficulty may be overcome by using pure reagents, relatively high concentrations, and long reaction times. Bromine substituents and careful identification and elimination of anhydride byproducts both greatly improve chromatographic purification, giving access to pure products amenable to a segment-doubling synthesis of sequences composed of up to 96 monomers. An efficient one-pot multibromination of helical oligomers is also reported.

Designing cooperatively folded abiotic uni- and multimolecular helix bundles

Abiotic foldamers, that is foldamers that have backbones chemically remote from peptidic and nucleotidic skeletons, may give access to shapes and functions different to those of peptides and nucleotides. However, design methodologies towards abiotic tertiary and quaternary structures are yet to be developed. Here we report rationally designed interactional patterns to guide the folding and assembly of abiotic helix bundles. Computational design facilitated the introduction of hydrogen-bonding functionalities at defined locations on the aromatic amide backbones that promote cooperative folding into helix-turn-helix motifs in organic solvents. The hydrogen-bond-directed aggregation of helices not linked by a turn unit produced several thermodynamically and kinetically stable homochiral dimeric and trimeric bundles with structures that are distinct from the designed helix-turn-helix. Relative helix orientation within the bundles may be changed from parallel to tilted on subtle solvent variations. Altogether, these results prefigure the richness and uniqueness of abiotic tertiary structure behaviour.