Synthetic Metals (v.158, #7)

The electrospinning technique was utilized to produce camphorsulfonic acid (HCSA) doped poly(o-toluidine) (POT)–polystyrene (PS) composite fibers in the non-woven mat form. HCSA doped POT–PS composite fibers were fabricated on an interdigited gold (Au) substrate for use as a chemical vapor sensor. The composite fiber sensor responded to volatile chemicals in different ways, depending on the polarity of sensing chemicals. The surface morphology of the non-woven composite fiber mat after chemical vapor sensing was unchanged. This study highlights that composite fibers comprised of polyaniline derivative and a spinnable polymer do have potential for use as chemical sensors due to their good solubility in common solvents and detectable electrical changes at low fiber contents.
Keywords: Electrospinning; Camphorsulfonic acid doped poly(o-toluidine)–polystyrene; Composite fibers; Sensors; Chemical vapors;

Influence of cluster composition on NLO properties of neutral cubane-like heterothiometallic clusters by Guodong Tang; Yuan Cao; Jinfang Zhang; Yu Zhang; Yinglin Song; Fengli Bei; Lude Lu; Chi Zhang (264-272).
A series of new candidates as nonlinear optical materials, tetra-nuclear heterobimetallic clusters [MOS3M3′Y(PPh3)3] (M = Mo, M′ = Ag, Y = Br 1; M = W, M′ = Ag, Y = I 2; M = Mo, M′ = Cu, Y = I 3; M = W, M′ = Cu, Y = I 4), have been synthesized by newly developed ligand-redistribution reaction for third-order nonlinear optical (NLO) studies. Single-crystal X-ray diffraction shows that clusters [MoX(μ3-S)33-Br)(AgPPh3)3] 1 and [WX(μ3-S)33-I)(CuPPh3)3] 4 (X = O0.5S0.5 1, O 4) adopt an isomorphous neutral cubane-like skeleton. Their optical nonlinearities were measured by Z-scan technique with an 8 ns pulsed laser at 532 nm. These clusters were found to exhibit effective nonlinear absorption, self-focusing effects and large optical limiting capabilities. The effective NLO susceptibilities χ (3) and the corresponding second-order hyperpolarizabilities γ of these clusters are also reported. The influence of cluster composition on NLO properties has been discussed accordingly.
Keywords: Neutral cubane-like clusters; Cluster composition; Nonlinear optical properties;

A new light-emitting poly(p-phenylenevinylene) (PPV) derivative containing trialkoxyalkyl substituents (TAA) as color tunable groups was synthesized through a Gilch polymerization, and the light-emitting properties of the polymer (TAA-PPV) were investigated. The emission of TAA-PPV was found to be highly blue-shifted to the green region, with peak absorption and band edge near 399 and 490 nm, respectively. The PL emission maximum of TAA-PPV thin films was found to be at approximately 493 nm. Light-emitting devices were fabricated with the configuration ITO (indium–tin oxide)/PEDOT/polymer/Ca/Al and produced very bright green emission. This device with TAA-PPV as the emissive layer had a maximum brightness of 3600 cd/m2 and a maximum power efficiency of 0.77 lm/W.
Keywords: Highly alkoxylated PPV; Steric hindrance; Blue-shifted emissions;

Observation of the solid-state formation of a TTF–CA complex by terahertz spectroscopy by Jun-ichi Nishizawa; Takenori Tanno; Takahiro Oohashi; Hiraku Watanabe; Yutaka Oyama (278-282).
The solid-state synthesis of a tetrathiafulvalene–chloranil (TTF–CA) complex was demonstrated, and progress in the formation of the complex was monitored using a GaP Raman terahertz (THz) spectrometer. Clear transitions in the THz absorption spectra indicated that the mixture of TTF and CA became the black phase TTF–CA complex. The results of X-ray diffraction, Raman scattering, and FTIR spectra are presented as supporting evidence.
Keywords: TTF–CA; Solvent-free reaction; Terahertz; Far infrared spectrometry; Molecular crystal; Charge-transfer complex;

Evidence of photoluminescence quenching in poly(3-hexylthiophene-2,5-diyl) due to injected charge carriers by Vipul Singh; Anil Kumar Thakur; Shyam Sudhir Pandey; Wataru Takashima; Keiichi Kaneto (283-286).
Photoluminescence spectra of poly(3-hexylthiophene-2,5-diyl) (P3HT) has been studied in forward and reverse bias direction in an indium tin oxide (ITO)/P3HT/Al Schottky device. It has been observed that photoluminescence quenching is relatively higher in forward direction and the quenching pattern gets reversed when a thin insulating layer of poly(4-vinylphenol) is coated on ITO. The observed behavior of photoluminescence quenching pattern has been explained on the basis of interaction of the injected charge carriers with the excitons generated in the bulk of P3HT together with the interaction of excitons with the applied electric field.
Keywords: Exciton; Photoluminescence; P3HT; Quenching;

Broad band and white phosphorescent polymer light-emitting diodes in multilayer structure by Kai-Chin Tang; Shin-Rong Tseng; Wei-Shan Li; Hsin-Fei Meng; Sheng-Fu Horng; Chian-Shu Hsu (287-291).
Efficient phosphorescent polymer light-emitting diode with poly(vinylcarbazole) (PVK) doped by two or three iridium complexes in single and bilayer structures are studied. With (tris-(2-4(4-toltyl) phenylpyridine) (Ir(mppy)3) as the green emitter and (1-phenylisoquinoline) (acetylacetonate) iridium(III) (Ir(piq)2) as the red emitter the efficiency is as high as 23 cd/A with broad band emission from 500 nm to 720 nm. For white emission a second layer is added with blue emitter ((III) bis[(4,-6-di-fluorophenyl-pyridinato)N,C2] picolinate) (FIrpic) doped in PVK. White light containing three spectral peaks results with efficiency 8.1 cd/A. As the second blue layer is replaced by the fluorescent (poly(9,9-dioctylfluorene)) (PFO) white emission with high color rendering index 86 is achieved. The efficiency is 5.7 cd/A with peak luminance 8900 cd/m2. For a given iridium complexes ratio the relative intensity of the green and red emission depends sensitively on the second blue layer.
Keywords: Phosphorescent; Multilayer; Polymer light-emitting diodes;

Highly fluorescent isomeric donor–acceptor molecules, 2-(4-phenyl-2-quinolyl)-10-methylphenothiazine (2PQMPT) and 3-(4-phenyl-2-quinolyl)-10-methylphenothiazine (3PQMPT), were synthesized in high yields (>85%) and found to exhibit a factor of 2.4 disparity in electroluminescence efficiency. Bright (10,000–25,000 cd/m2) and efficient (3.6–8.7 cd/A) green organic light-emitting diodes were realized from the two donor–acceptor molecules. The new molecules are good model systems for the study of structure–property relationships of donor–acceptor molecules for organic light-emitting diodes.
Keywords: Donor–acceptor material; OLED; Phenothiazine; Quinoline; Synthesis;

Solid-state structure of the naphthalene-based n-type semiconductor, and performance improved with Mo-based source/drain electrodes by Chia-Chun Kao; Pang Lin; Yu-Yuan Shen; Jing-Yi Yan; Jia-Chong Ho; Cheng-Chung Lee; Li-Hsin Chan (299-305).
The synthesis, single-crystal structures, and device performance of novel naphthalene-diimide are described. The crystal structure has revealed the importance of a withdrawing group on solid-state packing. Metal molybdenum use as source/drain (S/D) electrodes can improve the performance of the bottom-contact device. The bottom-contact device based on a material of N,N′-bis (4-trifluoromethoxybenzyl) naphthalene-1,4,5,8-tetracarboxylic acid diimide has a high mobility of 3.58 × 10−2  cm2  V−1  s−1, a threshold voltage of 1.3 V, and an on/off current ratio of 5.2 × 105.
Keywords: Organic thin-film transistors; n-Type; Naphthalene; Air-stable; Molybdenum;