The transition from the biexciton to the exciton can turn over the direction of the electric dipole of a polymericmolecule. This turning-over action combined with the photoinduced polarization reversion can be used as a switch. Theswitching speed is governed by the relaxation time of the turning-over process, which can be determined by a dynamicalsimulation.

Anong the present three types of electric field-induced luminescence we noticed similarities between the inorganicand organic materials in electric field intensity. In this high electric field range SiO2 has three functons: acceleration,excitation and multiplication of electrons. Based on the acceleration effect, cathodoluminescence-like emission of organicmolecules and polymers was found. By using the three functions of SiO2 or II-VI compounds and the heterojunction of inorganic and organic material we realized different variants of mixed excitation in electroluminescence.

New acetylene monomers, 6-{[(1-naphthylethynyl-4-phenyl)carbonyl]oxy}-1-pheny-1-hexyne (1), 2, 5-diethynyl-thiophene (3), and 4,4'-diethynylbiphenyl(6) were synthesized. Homopolymerization of 1 and copolycyclotrimerizations of 3and 6 with 1-heptyne and 1-octyne have been achieved with WCl6- and TaCl5-Ph4Sn catalysts, respectively, giving solublelinear disubstituted polyacetylene (2) and hyperbranched polyarylenes (5 and 8) with high molecular weights (up to 1.2×105) in high yields (up to 98%).The structures and properties of the polymers are characterized and evaluated by IR,NMR,TGA,UV,photoluminescence(PL),and electroluminescence (EL) analyses.All the polymers possess high thermal stability and emit strong blue light upon photoexcitation.The intensity of the emitted light is greater than that of poly(1-phenyl-1-octyne),a well-known highly luminescent disubstituted polyacetylene.Little aggregation-induced red shift in the PL was observed in the thin films of the polymers.By constructing a multi-layer EL device,high EL quantum yield (0.18%) has been achieved in 2,which are the best results for substituted polyacetylenes attainable so far.

The electroluminescence (EL) produced by a highly luminescent phosphorescent dye Cu4(C≡CPh)4L2 (L = 1.8-bis(di-phenylphosphino)-3, 6-dioxaoctane, Cu_4) doped polymer as emitting layer is reported. The effects o f the chargeinjection balance on the polymers, in particular, poly(N-vinylcarbazole) (PVK) have been studied by usingphotoluminescence and elecholuminescence spectroscopy. Changes in the emission spectra demonstrate the influence of thecharge injection balance on the formation ratio of triplet and singlet excitions.This provides a new technical approach to realize the color patterning in polymer LEDs.

Recent work demonstrated that efficient solar-energy conversion could be achieved in polymer photovoltaic cells(PVCs) based on interpenetrating bi-continuous networks. In this paper we present a comprehensive study on improvingenergy conversion efficiencies of PVCs based on composite films of MEHPPV and fullerene derivatives. Carrier collectionefficiency of ca. 30% el/ph and energy conversion efficiency of 3.9% were achieved at 500 nm. At reverse bias of 15 V, the photosensitivity reached 0.8A/W,corresponding to a quantum efficiency over 100% el/ph.These results suggest that high efficiency photoelectric conversion can be achieved in polymer devices with M-P-M structure.These devices are promising for practical applications such as plastic solar cells and plastic photodetectors.

Several series of fluorene-based light-emitting polymers with the emphasis on achieving efficient and stable bluelight emission are reported. Spiro-functionalization may narrow the emission spectra (with smaller tail at Ionger wavelengths)of fluorene homopolymers to provide purer blue emission. The thermal spectral stability of the polymers could also beimproved because of the elevation of the glass transition temperature caused by the spiro-functionalization. However,the excimer emission in fluorene homopolymers is not suppressed by the spiro-functionalization.Alternate copolymers of 9.9-dihexylfluorene and substituted phenylenes may emit efficient blue light both in solution and in film.The optical properties are dependent on the substitution on the phenylene ring.The alkoxy-substituted polymers displayed efficient PL and EL and good thermal spectral stability.The HOMO and LUMO energy levels of the polymers based on the backbone structure could be tuned in a wide range by attaching different functional groups on the phenylene ring.By attaching europium(III)complex at the ends of the side chains in the alternate copolymers,we have demonstrated a new approach to achieving red emission with a very narrow spectrum.The copolymers of 9,9-dihexylfluorene and thiophene and bithipphene with different substitutions were also synthesized to study the effect of substitution and regioregularity on the optical and other physical properties of the polymers.

Two new blue light-emitting PPV-based conjugated copolymers containing both an electron-withdrawing unit(triazole-TAZ) and electron-rich moieties (carbazole-CAR and bicarbazole-BCAR were prepared by Wittig condensationpolymerization between the triazole diphosphonium salt and the corresponding dialdehyde monomers. Their structures andproperties were characterized by FT-IR, TGA, DSC, UV-Vis, PL spectroscopy and electrochemical measurements. The resulting copolymers are soluble in common organic solvents and thermally stable with a Tg of 147℃ for TAZ-CAR-PPV and of 157℃ for TAZ-BCAR-PPV.The maximum photoluminescence wavelengths of TAZ-CAR-PPV and TAZ-BCAR-PPV film appear at 460 nm and 480 nm,respectively.Cyclic voltammetry measurement demonstrates that TAZ-BCAR-PPV has good electrochemical reversibility,while TAZ-CAR-PPV exhibits the irreversible redox process.The triazole unit was found to be an effective π-conjugation interrupter and can play the rigid spacer role in determining the emission colour of the resulting copolymer.