Tian-An Chen

Hopping transport in doped conducting polymers in the insulating regime near the metal-insulator boundary: polypyrrole, polyaniline and polyalkylthiophenes

Abstract Transport data for polypyrrole-hexafluorophosphate (PPy-PF6), protonated polyaniline and iodine-doped regio-regular polyalkylthiophenes (PATs), all in the insulating regime near the disorder-induced metal-insulator (M-I) boundary, are presented and analyzed. These doped conducting polymers have the transport properties of a Fermi glass insulator; the disorder being characterized by the resistivity ratio, ρr  ρ(1.4 K)/ρ(300 K). In the regime close to the M-I transition (ρr 103), ρ(T) shows two distinctly different behaviors. In homogeneous material, Motts VRH conduction is recovered. In inhomogeneous samples, where ‘metallic island’ are formed after partial dedoping or by strong morphological disorder, ln ρ ∝ (T 0 ′/T) 1 2 , characteristic of a granular system.

Polyalkylthiophenes with the smallest bandgap and the highest intrinsic conductivity

Abstract The physical properties (electrical absorptions, bandgaps, electroconductivities) of a completely regioregular head-to-tail polyalkylthiophene and a totally regiorandom isopolymer are reported. The regioregular polyalkylthiophenes exhibit, to date, the smallest bandgap (1.7 eV) and the highest intrinsic conductivity (10−6 S/cm for undoped polymer) of polyalkylthiophenes. The bandgap is 0.3–0.5 eV lower than that of normal polyalkylthiophenes (2.0–2.2 eV) and the intrinsic conductivity is three orders of magnitude higher than that of normal polyalkylthiophenes (10−9–10−10 S/cm). The regioregular polymer also exhibits a large iodine-doped conductivity (average 1350 S/cm) of polymer film. A bipolaron gap state is generated in the iodine-doped regioregular polyalkylthiophene film by chemical oxidation, while it fails for the regiorandom polyalkylthiophene.

Enhanced electroluminescence from semiconducting polymer blends

Abstract We demonstrate the enhancement of electroluminescence (EL) from blends of poly(3-hexylthiophene) (P3HT) in poly(2-methoxy-5-(2′-ethylhexoxy)-1,4-phenylene vinylene) (MEH-PPV). The external EL quantum efficiency η of Ca/P3HT:MEH-PPV/ITO diodes initially increases with P3HT content and goes through a maximum at η = 1.7% photons/electron with only 1 wt.% P3HT; greater than in Ca/MEH-PPV/ITO by a factor of two to three and greater than in Ca/P3HT/ITO by more than three orders of magnitude. At 4 V forward bias, these devices emit signal-red light with brightness of about 220 cd/m2.

Electroluminescence from blend films of poly(3-hexylthiophene) and poly(N-vinylcarbazole)

Electroluminescence (EL) is reported from blends of head-to-tail poly(3-hexylthiophene) (P3HT) and poly(N-vinylcarbazole) (PVK); light-violet color emission is observed (a mixture of blue and red). Since P3HT and PVK are soluble in common organic solvents, light-emitting diodes (LEDs) can be fabricated by spin-casting films of the polymer blends from solution without subsequent processing or heat treatment. Calcium and indium-tin oxide (ITO) were used as the electron-injection and hole-injection electrodes, respectively. The EL quantum efficiency was enhanced by blending, with an optimized value of 0.2% photons/electron in blend films with about 2 wt.% P3HT; i.e. greater than in pure PVK by approximately a factor of four and greater than in pure P3HT by more than two orders of magnitude.

Room temperature stable 3-lithiothiophene: a facile synthesis of 3-functional thiophenes

Abstract 3-Functionalized thiophenes were readily prepared by reacting electrophiles with 3-lithiothiophene at room temperature. 3-Lithiothiophene was found to be stable in hexane at room temperature.

Functionalization of halogenated polystyrene resins utilizing highly reactive calcium

Polymeric organocalcium reagents were prepared via the oxidative addition of highly reactive calcium, prepared from the lithium biphenylide reduction of calcium iodide, to cross-linkedp-bromopolystyrene,p-chloropolystyrene,p-fluoropolystyrene, and chloromethylated polystyrene. These organocalcium reagents react with a variety of electrophiles to yield functionalized polymers.