Y.Q. Liu

Color-tunable polymeric light-emitting diodes based on blend of CN-PPV and PVK

Abstract Polymeric light-emitting diodes (LEDs) fabricated by sandwiching the blend of cyano-substituted poly( p -phenylene vinylene) (CN-PPV) and poly ( N -vinyl carbazole) (PVK) between indium-tin oxide (ITO) and Al are reported. The emission color of the device is tunable. At lower applied voltage, the color is blue, mainly coming from PVK. As the voltage increases, the contribution from CN-PPV gradually increases, and the emission color red-shifts to orange but the electroluminescence intensity of the device decreases. The doping ratio of CNPPV to PVK has an effect on both the turn-on voltage and the ideality factor of the devices.

Synthetic Molecular Rectifier of a Langmuir–Blodgett Film Based on a Novel Asymmetrically Substituted Dicyano-tri-tert-butylphthalocyanine

A novel asymmetrically substituted dicyano-tri-tert-butylphthalocyanine ((CN)2BuPc) with rectifying behavior has been synthesized. The morphology and conductive properties of (CN)2BuPc Langmuir–Blodgett (LB) films on mica and highly ordered pyrolytic graphite (HOPG) substrates were studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM), in air at 22 °C. The average area of each (CN)2BuPc molecule obtained from the AFM topography in situ is ca. 73.6 A2, which is in good agreement with the result of ca. 74 A2 obtained from the π–A isotherm curve of a LB film. This indicates that the molecules are standing edge-on, tilted by 38° against the surface normal of the substrate. The conductive properties for the 7-layer LB films of (CN)2BuPc were studied by STM with a tungsten tip. The asymmetric I–V curve revealed a type of rectifying behavior for a negative and a positive bias. A feature model of the intramolecular and intermolecular charge transfer is presented. It not only interprets electron transfer from electron-donor to electron-acceptor molecules via a molecular “bridge”, but also the tunneling effect through intermolecular charge transfer.

The synthesis of aminotri-tert-butyl phthalocyanine and its gas sensitivity to nitrogen dioxide

Aminotri-tert-butyl phthalocyanine (AmBuPc) is a new asymmetrical phthalocyanine, which possesses three tert-butyl groups and one amino-group. All the substituents are electron-donating ones and have a strong electron-donating ability when they interact with oxidizing gases, such as NO2. We report its synthesis and its gas sensitivity to nitrogen dioxide, and reveal the electrochemical properties of this compound.

Synthesis and Langmuir-Blodgett film of an alkyl substituted thiophene oligomer

Abstract α-Hexadecylterthiophene (C 16 -3T) was synthesized and its chemical structure was confirmed by elemental analysis, IR and MS. Fabrication of Langmuir-Blodgett (LB) films of C 16 -3T was described. The molecules can form stable monolayer at air-water interface with a collapse surface pressure up to 33 mN/m. The transfer ratios of 0.6–1.0 were obtained for an 18-layers LB film. The UV-visible absorption spectrum of C 16 -3T as LB film is quite different in shape from the spectrum in solution, indicating that the intermolecular interaction is occurred in the LB system. Conductivity of the LB film along the parallel direction of the substrate at room temperature is 10 −3 S/cm and can be increased by one order of magnitude on doping with iodine.

Electroluminescence devices made with poly(alkylthiophenes)

Abstract In our previous papers, we reported the synthesis of various poly(3-alkylthiophenes) derivatives with different side chain length, fabrication of their Langmuir-Blodgett films conductivities and Schottky diodes. Here, we extend our research to their electroluminescent properties. Multilayer light-emitting diodes composed of poly(3-octylthiophene) as light-emitting layer and hole transport layer are constructed. The current-voltage and brightness-voltage characteristics as well as the electroluminescent spectra are investigated and discussed.

Influence of fabrication process on the performance of light-emitting diodes

We have investigated the influence of device fabrication process on the performance of poly (p-phenylene vinylene) (PPV) and poly (N-vinyl carbazole) (PVK) blended with triphenylamine (TPA) (PVK:TPA)-based light-emitting diodes by constructing various devices with different structures and treated under different conditions. Thermal treatments make modifications to the contacts, affect the electrical properties of the polymer, change the rectification ratio by orders of magnitude, and affect the efficiency of the devices. Partially converted PPV improved the efficiency due to short conjugated length, but results in the stability of the devices to be compromised. Structure of PVK:TPA/PPV unbalances the injection of holes and electrons, but lowers the turn-on voltage.

STM studies of 1D smectic row of a novel asymmetrically substituted phthalocyanine on HOPG

A novel asymmetrically substituted dicyano-tri-tert-butyl-phthalocyanine (CN) 2 BuPc was self-physiosorbed on a highly ordered pyrolytic graphite (HOPG) substrate. The morphology of a 1D-smectic structure with two rows was obtained from the self-physiosorbed layer by STM in air at 22°C. Suggesting that the 1D-smectic structure grew up along the crystallization direction of HOPG (111) surface in an epitaxial style. The I-V characteristic was estimated and reveals an asymmetrical behavior. In the 1D-smectic structure, a phenomena with negative conductivity was observed at ac. -0.9 V, It might be explained that the sum role of the molecular separate level and tunneling process would create the physical phenomena. These studies imply an important role of interactions between molecule and substrate or molecule and molecule for some material systems in the self-physiosorbed and crystallizing process on an ordering substrate.