Guangming Wang

Effect of aqueous and organic solvent ratio on the electropolymerization of bithiophene in the mixed solutions

Abstract The use of suitable ratio of water to acetonitrile could lower the onset oxidation potential of bithiophene to about 0.6 V vs. Ag/AgCl in the aqueous/organic mixed solution. This means that bithiophene can be electropolymerised at very low potential in such solutions, which is usually unachievable in pure organic media. When the current density for electropolymerisation was kept constant as 1.0 mA/cm 2 , the electropolymerization potentials for bithiophene could be tuned to stable values of 0.8, 0.9, and 0.94 V by keeping the volume ratio of water to acetonitrile as 2:1, 1:1, and 1:4, respectively in the mixed solution. Evidence shows that the chemical structure of polybithiophene synthesised by this technique is very similar to that of the polymer formed in organic media. The volume ratio of water to acetonitrile has a significant effect on electropolymerization of bithiophene as well as on the electrochemical properties and morphology of the polybithiophene films.

Electroluminescent properties of a derivative of quinquepyridine

Abstract Electroluminescent (EL) properties of 6, 6 ⁗ -dimethyl-4 ′ ,4 ‴ -diphenyl-2,2 ′ :6 ′ ,2 ″ :6 ″ ,2 ‴ : 6 ‴ ,2 ⁗ -quinquepyridine (DMDPQPY) have been examined. The EL results of typical single layer devices indicate that emitting layer thickness can influence the emission wavelength. The introduction of a hole transporting layer in the double layer device enhances the luminance greatly, showing a better charge balance. It is proposed that 2,6-linked poly(oligo) pyridine derivatives are promising to form a new class of EL material both as emitter and as carrier transporter.

Effect of deposition current density on the effectiveness of electropolymerized hole-transport layer in organic electroluminescent device

Polybithiophene (PBTh) films electropolymerized at different current densities were used as hole-transport layer in the electroluminescent (EL) devices. It was found that the current density used for depositing PBTh film greatly affects the surface structure of the film, which determines the effectiveness of the PBTh film as the hole-transport layer used in the EL device on enhancing EL intensity and efficiency. Evidences show that for a high effective EL device there is an optimal current density for depositing the PBTh films as the hole-transport layer.

Influence of thickness of electrochemically deposited hole-transport film on electroluminescent properties

Abstract.Polybithiophene (PBTh) film was used as a hole-transport layer in an electroluminescent (EL) device. The PBTh was electropolymerized on indium tin oxide (ITO)-coated glass acting as a working electrode. From the change of full width at half maximum (FWHM) of the EL spectrum with the thickness of the PBTh film, it could be deduced that the PBTh film efficiently blocks the injection of electrons into the ITO electrode. The thickness of the hole-transport layer used in the EL device has a significant influence on the EL intensity and efficiency. Experimental data showed that there is an optimal thickness of the electrodeposited PBTh-hole-transport layer for high-efficiency EL devices.

Synthesis and optical properties of derivatives of oligobipyridines

Two oligobipyridly derivatives (L1, L2) which belong to partially conjugated oligomers in structure, were synthesized and found to show strong photoluminescence. In its as-obtained powder states, L1 shows an emission at 403 nm under the excitation of 365 nm; while when mixed with KBr, it shows one emission peak at 402 nm and one shoulder at 389 nm; and in its chloroform solution, it emits with two peaks at 344 nm and 356 nm. The as-obtained powder state of L2 emits with a peak at 418 nm under the excitation of 367 nm, while its doped state in KBr plate has two emissions at 403 nm and 423 nm; in its chloroform solution, two peaks at 393 nm and 414 nm appear under the excitation of 364 nm light. Films of L2 fabricated by vacuum evaporation emit at 406 nm and 428 nm. Both compounds show emission in the range of deep blue or violet color. It is proposed that one way to obtain blue emitting materials is to shorten the conjugation length in the polymeric and oligomeric structures. Silver complex of L1 show emission at 445 nm under the excitation of 348 nm. EL properties of L2 were studied preliminarily.

Influence of the hole-carrier layer controlled by electrochemical method on electroluminescence

Two-layer light emitting devices were fabricated using electrochemical deposited polybithiophene (PBTh) as the hole-transport layer and spin coated blend of polyoctylthiophene and a butadiene derivative as the emitting layer. It was found that the current density used for depositing polybithiophene greatly affects the effectiveness of the PBTh films as the hole-transport layers in enhancing the electroluminescent (EL) intensity and efficiency. Through analyzing the oxidation-reduction properties and conductivity of the PBTh films and the EL efficiency of the device, it can be concluded that there is an optimal current density for depositing the PBTh hole transport layer for the El devices.