Xian Tao

Synthesis and memory characteristics of highly organo-soluble polyimides bearing a noncoplanar twisted biphenyl unit containing aromatic side-chain groups

Two novel 3′,4′,5′-trifluorobiphenyl-based aromatic polyimide monomers, 2,2′-bis[4′-(3′′,4′′,5′′-trifluorophenyl)phenyl]-4,4′-biphenyl diamine (BTFBPD) and 2,2′-bis[4′-(3′′,4′′,5′′-trifluorophenyl)phenyl]-4,4′,5,5′-biphenyltetracarboxylic dianhydride (BTFBPDA) were synthesized. Two fluorinated polyimides (PIs), PI(BTFBPD-DPBPDA) and PI(BTFBPD-BTFBPDA) were prepared via a two-step procedure using BTFBPD reacting with 2,2′-diphenyl-4,4′,5,5′-biphenyltetracarboxylic dianhydride (DPBPDA) and BTFBPDA, respectively. BTFBPD was characterized with single crystal X-ray diffraction analysis and the geometric parameters showed the noncoplanar twisted character. PIs exhibited highly organo-solubility and thermal stability. The PI films sandwiched between an indium-tin oxide(ITO) bottom electrode and Al top electrode exhibited two accessible conductivity states and can be switched from the low-conductivity to the high-conductivity. The memory devices with the configuration of Al/PI(BTFBPD-DPBPDA)/ITO exhibited a flash type memory capability, whereas the Al/PI(BTFBPD-BTFBPDA)/ITO presented a write once read many times (WORM) memory capability. The fabricated devices showed low turn-on threshold voltages of −1.3 V (PI(BTFBPD-DPBPDA)) and −1.7 V (PI(BTFBPD-BTFBPDA)) and both ON/OFF current ratios on the order of 103 to 104.

Nonvolatile memory devices based on polyimides bearing noncoplanar twisted biphenyl units containing carbazole and triphenylamine side-chain groups

Two novel polyimides, PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA), consisting of alternating electron-donating 2,2′-bis[4-(9H-carbazol-9-yl)phenyl]- or 2,2′-bis[4-(diphenylamino)phenyl]-substituted biphenyl moieties and electron-accepting phthalimide moieties were synthesized and characterized. These polyimides are thermally stable with 5% weight loss over 500 °C and the glass transition temperatures of the polyimides were found to be 293 °C. The optical band gaps of PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA) were 3.42 and 3.30 eV, respectively, indicating the significance of the linkage groups. The estimated energy levels (HOMO, LUMO) of PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA) were (−5.51, −2.10) and (−5.22, −2.02) eV, respectively. Resistive switching devices with the configuration of Al/polymer/ITO were constructed from these polyimides by using the conventional solution coating process. The as-fabricated PI(CzBD-BTFBPDA) film exhibited a nonvolatile bipolar write-once–read-many times (WORM) memory character, whereas devices with the PI(TPABD-BTFBPDA) film showed “write–read–erase” flash type memory capability. The ON/OFF current ratios of the devices were both around 106 in the ambient atmosphere. The mechanisms associated with the memory effect were further elucidated from the density functional theory (DFT) method at the B3LYP level with the 6-31G(d) basis set. The present study suggested that the tunable switching behavior could be achieved through the appropriate design of the donor–acceptor PIs structure to have potential applications for memory devices.

Organophosphine/phosphite stabilized disilver(I) methanedisulphonates: synthesis, solid state structures and their potential use as MOCVD precursors

New disilver(I) methanedisulphonate complexes [CH(2)(SO(3))(2)Ag(2)·L(n)] (L = PPh(3); n=2, 2a; n=3, 2b; n=4, 2c; n=5, 2d; n=6, 2e; L=P(OEt)(3); n=2, 2f; n=4, 2g; n=6, 2h) were prepared by the reaction of [CH(2)(SO(3))(2)Ag(2)], which could be synthesized from methanedisulphonic acid and Ag(2)CO(3) in water, with triphenylphosphine or triethylphosphite in dichloromethane under a nitrogen atmosphere. The solid state structures of three complexes 2c, 2d and 2f were determined by single X-ray structure analysis. Hot-wall metal organic chemical vapor deposition (MOCVD) experiments were carried out at 395 °C, 420 °C and 450 °C using 2g as precursor for the deposition of silver films, respectively. The silver film with high purity obtained at 420 °C is dense and homogeneous, which is composed of many well isolated, granular particulates spreading all over the substrate surface.

Synthesis, structure, and catalytic activity of lanthanide Gd(III) and La(III) complexes with N-(cyclohexyl)isopropyl amidate ligand

Two new lanthanide amidate complexes, {Gd2[Cy(NCO)iPr]6} (1) and {La2[Cy(NCO)iPr]6[Cy(HNCO)iPr]} (2) (iPr = isopropyl, Cy = cyclohexyl), have been synthesized in good yields by silylamine elimination reaction between Gd[N(SiMe3)2]3 or La[N(SiMe3)2]3 and N-(cyclohexyl)isopropyl amide. Complexes 1 and 2 have been characterized by NMR, elemental analyzes, and X-ray diffraction. The molecular structures of {[Cy(NCO)iPr]Gd[μ2-Cy(NCO)iPr]3Gd[Cy(NCO)iPr]2} (1) and {[Cy(NCO)iPr]La[μ2-Cy(NCO)iPr]3La[Cy(NCO)iPr]2[Cy(HNCO)iPr]} (2) exhibit a dimer structure with three μ2-O bridging bonds that look like a windmill. Additionally, 2 formed an intramolecular N–H···O hydrogen bond via a neutral amide. The catalytic properties of 1 and 2 for ring-opening polymerization (ROP) of ε-caprolactone have been studied. The results show that 1 and 2 are efficient catalysts for the ROP of ε-caprolactone.

Bis[μ- N , N ′-bis(quinolin-8-yl)pyridine-2,6-dicarboxamido]dizinc(II) dichloromethane disolvate

The title compound, [Zn(2)(C(25)H(15)N(5)O(2))(2)]·2CH(2)Cl(2), is a dinuclear double-helical complex which lies on a crystallographic twofold axis. In the complex, both ligands are partitioned into two tridentate domains which allow each ligand to bridge both metal centres. Each Zn(II) atom is six-coordinated in a distorted octahedral environment formed by two amide N atoms, two quinoline N atoms and two pyridine N atoms from two different ligand molecules, with the central pyridine ring, unusually, bridging two Zn(II) atoms. The deprotonated ligand is not planar, the amide side chains being considerably twisted out from the plane of the central pyridine ring.

Heteroleptic lanthanide amide complexes bearing carbon-bridged bis(phenolate) ligands: synthesis, structure and their application in the polymerization of ε-caprolactone

A convenient method for the synthesis of anionic lanthanide amide complexes bearing carbon-bridged bis(phenolate) ligands H2L [L = (o-CH3)PhCH(C6H2-3-tBu-5-R-2-O)2; R = Me, L = L1 and R = tBu, L = L2] is described. The bis(phenolato)lanthanide complexes LLnN(SiMe3) [L = L1, Ln = La (1), Ln = Gd (2) and L = L2, Ln = La (3), Ln = Gd (4)] were synthesized in nearly quantitative yields by the reaction of Ln[N(SiMe3)2]3 (Ln = La or Gd) with H2L in a 1 : 1 molar ratio in THF at 60 °C. The bis(phenolato)lanthanide pyrazolato complexes LLnPzMe2(THF)3 [L = L1, Ln = La (5), Ln = Gd (6) and L = L2, Ln = La (7), Ln = Gd (8)] were obtained in high yields by further reacting the obtained LLnN(SiMe3) with another 1 equiv. of 3,5-dimethylpyrazole (Me2PzH). Meanwhile, the complexes LLnPzMe2 can also be synthesized by the direct reaction of Ln[N(SiMe3)2]3 with H2L and Me2PzH in 1 : 1 : 1 molar ratio in situ in THF. Complexes 5–8 have been characterized by X-ray crystal structural analysis. The central lanthanide metal atom is seven-coordinated by one bis(phenolate) ligand, one pyrazole ligand and three THF molecules in a distorted pentagonal bipyramid. The catalytic activity of compounds 1–8 in the ring-opening polymerization of e-caprolactone was studied. The catalytic mechanism was studied and discussed as well.

Preparation and Photoluminescent Properties of Doped Ternary Europium Complexes Bearing 1-(Naphthalen-2-yl)-3-phenylpropane-1, 3-dione

Rare earth (RE) ternary complexes of Eu0.5Ln0.5(NPPD)3×DPQ (HNPPD = 1-(naphthalen-2-yl)-3-phenylpropane-1, 3-dione; DPQ = Dipyridobenzoquinone; Ln3+ = Nd3+, Er3+, Ce3+, Dy3+), Eu1-xYx(NPPD)3×DPQ and Eu1-xLux(NPPD)3×DPQ (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9) were synthesized by the reaction of RECl3×6H2O with HNPPD and DPQ in stoichiometry. The UV-vis and fluorescence properties of the complexes were investigated. The experimental results show that the luminescence efficiency of Eu3+ complexes was enhanced by doping some other lanthanide ions.