Yangang Liu

Electrochemical Growth of Nanopillar Zinc Oxide Films by Applying a Low Concentration of Zinc Nitrate Precursor

Zinc oxide nanopillars with a single crystalline structure on the indium tin oxide substrate were prepared by using an electrodepositing process in lower concentrations of aqueous Zn(NO 3 ) 2 and 0.1 M KCl solutions. Surface structure and crystal orientation of the prepared ZnO films were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, respectively. By varying the electrolyte composition, the morphology and crystal orientation of ZnO films may be changed dramatically. Well-oriented ZnO nanopillars can be obtained at a relatively low concentration of zinc ion in the electrolyte, and at a lower potential. A bandgap energy change of grown ZnO with different Zn(NO 3 ) 2 concentrations was observed. The effects of electrodepositing potential, deaerating, and annealing are also discussed.

Nonlinear optical chromophores with good transparency and high thermal stability

In order to improve the transparency and thermal stabilities of nonlinear optical (NLO) chromophores, new materials based on the azo benzene chromophore having 1,3,5-triazine groups were prepared. Their NLO properties were experimentally derived using a two-level model. Compared with corresponding NLO chromophores p-nitroaniline (PNA) and C.I. Disperse Red 1, the newly synthesised chromophores displayed better transparency and higher thermal stability. The reaction of a new NLO chromophore with a dianhydride resulted in polyimide that was converted to a poled polymer which had a d33 value of 69 pm/v, a Tg of 225°C, decomposition temperature of 354°C and an absorption cut-off below 450 mm, indicating its ability for harmonic generation application in the blue and green regions.

Design and synthesis of poly(p-phenylenevinylene) derivative with triphenylamine segments on polymer backbone

A new approach to the synthesis of conjugated polymer with triphenylamine (TPA) segments was presented. Electrochemical reversibility and thermal stability were found for this polymer. The introduction of TPA segments to the polymer backbone has modified its optical and electrochemical properties. The estimated highest occupied molecular orbital (HOMO) of 5.4 eV from electrochemical measurement suggested that it could be a low hole injection barrier when used as the active layer in the polymer LED. High brightness emission and improved efficiency were obtained in a double-layer device.

Synthesis and characterization of side-chain polyimides for second-order nonlinear optics via a post-azo-coupling reaction

A two-step, generally applicable synthetic approach for nonlinear optical (NLO) side-chain polyimides was developed. This included the preparation of a preimidized, organosoluble polyimide with benzene moiety pendant from main chains, followed by the covalent bonding of the NLO chromophores onto the polyimide backbone via a post-azo-coupling reaction. The degree of functionalization of polyimides was estimated by UV-VIS spectroscopy. The glass transition temperature (Tg) of a polyimide decreased by only 10–20°C after the functionalization, which was much smaller than the decrease in Tg when the chromophores were chemically bonded to the polyimide main chains through an ether linkage using a post-Mitsunobu condensation. The solubility and thermal stability of polyimides were also studied.

Crystal structure of p-formylphenyl, di(p-methylphenyl)amine, and p-bromophenyl, di(o-bromo-p-methylphenyl)amine

Abstractp-Formylphenyl, di(p-methylphenyl)amine (1), and p-bromophenyl, di(o-bromo-p-methylphenyl)amine (2) were prepared and characterized by X-ray crystallography. Formyl-substituted triphenylamine(1) crystallizes in the monoclinic space group P21/c with a = 9.068(1), b = 17.115(2), c = 11.297(2) Å, β = 106.73(1)°, V = 1679.0(5) Å3 and Z = 4. Bromo-substituted compound 2 crystallizes in the monoclinic space group P21/n with a = 16.170(4), b = 7.9477(8), c = 16.906(4) Å, β = 117.67(2)°, V = 1924.1(7) Å3 and Z = 4. The N atoms deviate slightly from the plane of the bonded C atoms and the benzene ring planes are rotated by 25–67° to avoid overlap of the ortho-substituted atoms. The major force of crystal formation comes from the multiple phenyl embraces (MPE).

Fabrication and charge/energy-transfer study of 4,7-bis(4-triphenylamino)benzo- 2,1,3-thiadiazole/CuPc composite films

Composite films of 4,7-bis(4-triphenylamino)benzo-2,1,3-thiadiazole (TBT) and copper phthalocyanine (CuPc) are fabricated via protonation-coelectrophoretic deposition from nitromethane solutions of TBT/CuPc mixture in the presence of trifluoroacetic acid as a protonation reagent. A nanospheres–nanowires interpenetrating network structure is obtained when the molar percentage of TBT is 70%. Furthermore, the existence of TBT makes α-phased CuPc be partly transformed into the β-phase, and simultaneously, CuPc disorganizes the TBT unit cells. The blue shift on the absorption edge of TBT and the significant fluorescence quenching in the composite films indicate energy/charge transfer and donor–acceptor (D–A) heterojunction formation. Then these results are proved from another point of view: the mutual overlap of absorption and emission spectra of TBT and CuPc lead to a bidirectional Forster resonance energy transfer at the interface; the molecular energy levels calculated from the results of cyclic voltammetry theoretically determine that there exist a D–A heterojunction and charge transfer from TBT to CuPc. Finally, from the investigation of the field-induced surface photovoltage spectra, it can be concluded that this charge transfer results in efficient dissociation of the photoinduced excitons in the composite films, followed by the generation of a strong photovoltage response.

Nanocrystalline Films Formation of 4,7-Bis(4-triphenylamino)benzo-2,1,3-thiadiazole through Electrophoretic Deposition

The nanocrystalline films of an amorphous triphenylamine derivative have been firstly formed by a facile electrophoretic deposition (EPD) method from a solution of protonated 4,7-bis(4-triphenylamino)benzo-2,1,3-thiadiazole. The films are composed of nanoparticles which diameters are controllably varied from 20 to 200 nm. Compared with spin-coating films, EPD films possess lower band gap and higher energy level of the highest occupied molecular orbital (HOMO), which means superior intermolecular charge-transfer ability and more excellent hole-transporting property. The facile method for preparing nanocrystalline films could also spread to other amorphous triphenylamine derivatives.