Polyfluorenes containing pyrazine units:Synthesis,photophysics and electroluminescence

A series of conjugated copolymers of 9,9-dioctylfluorene and symmetrical pyrazine unit (BY) were synthesized by Suzuki copolymerization and were used as novel light-emitting materials in PLEDs.Efficient energy transfer was observed in both thin film and solution.Compared with the lowest occupied molecular orbital (LUMO) energy level of the polyfluorenes homopolymer (PFO),the lower LUMO energy levels of copolymers indicated that the introduction of the BY unit would be benefit to electron injection.The turn-on voltages of their single-layer electroluminescent (EL) devices (ITO/PEDOT/polymer/LiF/Al) were at 6.1-4.0 V,which were much lower than that of PFO (7.0 V).The maximum brightness,current efficiency,and external quantum efficiency of all PFBY copolymers were higher than those of the PFO homopolymer.The single-layer device of PFBY5 was the best one in the copolymers,with a maximum brightness of 485 cd/m2,a current efficiency of 0.29 cd/A,and an external quantum efficiency of 0.10%.The introduction of PVK and TPBI for the multilayer device of PFBY5 increased the device efficiencies,which showed a maximum brightness of 3012 cd/m2,a maximum current efficiency of 1.81 cd/A,and an external quantum efficiency of 0.66%.

SYNTHESIS OF POLYFLUORENES BEARING LATERAL PYRENE TERMINATED ALKYL CHAINS FOR DISPERSION OF SINGLE-WALLED CARBON NANOTUBES

Two kinds of polyfluorenes 19earing two lateral pyrene terminated alkyl chains and two alkyl chains per repeating unit were synthesized by Suzuki polycondensation and used to disperse single-walled carbon nanotubes （SWCNT） in organic solvents. Stable polymer-SWCNT complex can be formed via the multivalent π-π stacking in＂.eraction of the lateral pyrene functional groups and the polyfluorene backbone with the outer surface of carbon nanotubes; meanwhile the lateral alkyl chains can impart good solubility to the complex. As expected, polyfluorenes bearing lateral pyrene functional groups and octyl chains exhibited much higher ,zarbon nanotube solubility in common organic solvents than the corresponding polyfluorenes bearing only octyl chains. Photophysical studies indicated that the formation ofpalymer-SWCNT complex can effectively quench the fluorescence of polyfluorenes.

Bipolar Blue Light-emitting Polyfluorenes Containing Dibenzothiophene-S,S-dioxide/Carbazole Units

Bipolar blue light-emitting polyfluorenes（PFSO-Cz） containing electron-deficient dibenzothiophene-S,S- dioxide（SO） and electron-rich carbazole（Cz） unit were synthesized. All the polymers show a high thermal stability with the decomposition temperatures over 400 ℃ and higher photoluminescence quantum yields. The highest occupied molecular orbital energy levels（EHMH＇s） slightly enhance and the lowest unoccupied molecular orbital energy levels（ELuMo＇S） gently depress with the increase of Cz content in the polymers. PL spectra of the polymers display remarkable red shift and broadening with the increase of solvent polarities, indicating significant intramolecular charge transfer（ICT） effect in the polymers. Electroluminescence（EL） spectra of the polymers exhibit a broadening tendency with increasing the content of Cz unit in the polymers. The superior device performances were obtained with the maximum lumhlous efficiency（LEmax） of 5.2 cd/A, the maximum external quantum efficiency（EQEmax） of 4.8% and the Internationale de I＇Eclairage（CIE）（x,y） coordinates of （0.16, 0.17） for PFSO15-Cz10 based on the single-layer device of ITO/PEDOT：PSS/EL/CsF/A1. The results indicate that the efficient bipolar blue light-emitting polyfluorenes are also constructed by Suzuki copolymerization using the monomers in common use.

Blue light-emitting polyfluorenes containing dibenzothiophene-S,S-dioxide unit in alkyl side chain

Blue light-emitting polyfluorenes containing dibenzothiophene-S,S-dioxide(SO) unit in alkyl side chain(PF-FSOs and PF-CzSOs) were synthesized. All the polymers show high thermal stability with the decomposition temperatures over400 °C. The highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) energy levels of the copolymer slightly decrease with the increase of SO content in side chain. PL spectra of the polymers show slightly red shift and broadening with the increase of solvent polarities, indicating unremarkable intramolecular charge transfer(ICT) effect in the polymers containing SO unit in alkyl side chain. EL spectra of the polymers are almost unchanged in the current densities from 100 to 400 mA cm.2, indicating the superb EL stability of the resulted polymers. The EL spectra of the copolymers exhibit obvious blue-shift and narrowing with the CIE of(0.18, 0.11) for PF-FSO10 and(0.17, 0.11) for PF-CzSO10, respectively,compared with PF-SO10 containing SO unit in main chain with the CIE of(0.16, 0.17) and PFO with the CIE of(0.18, 0.18).The superior device performances were obtained with the luminous efficiency(LEmax) of 1.17 and 0.68 cd A.1 for PF-FSO15 and PF-CzSO20, respectively, compared with the LEmax of 0.37 cd A.1 for PFO. The results indicate that linking SO unit to alkyl side chain of the polyfluorene is a promising strategy for efficient blue light-emitting polymers.

Green-emitting Polyfluorenes Containing Hexylthiophen-dibenzothiophene-S,S-dioxide Unit with Large Two-photon Absorption Cross Section

Green light-emitting polyfluorenes containing 3,7-bis（4-hexylthiophen-2-yl）dibenzo[b,d]thiophene 5,5-dioxide（DHTSO）unit were synthesized.All the resulted polymers show high thermal stability with the decomposition temperatures（T_d）over 420°C and the glass transition temperatures（T_g）over 75°C.The polymers exhibit the enhanced highest occupied molecular orbital（HOMO）energy levels and the depressed lowest unoccupied molecular orbital（LUMO）energy levels with the increase of DHTSO unit in polymers.The photoluminescence（PL）spectra of the polymers show positive solvatochromism in solution with the variation of solution polarities,indicating remarkable intramolecular charge transfer（ICT）effect in the polymers containing DHTSO moiety.The fluorescence quantum yields（（37）_（PL））are in the range of 34%-67%for PF-DHTSOs in film.All polymers possess two photon absorption（TPA）properties,and the TPA cross sections（？_2）are enhanced with increasing DHTSO unit in polymers.The highest？_2 is 2392 GM for PF-DHTSO15 in chloroform solution upon 740 nm excitation.The device of PF-DHTSO15 shows green emission with the Commission Internationale de L’.Eclairage（CIE）coordinates of（0.26,0.59）,and the maximum luminous efficiency（LE_（max））of 10.8 cd·A^（-1） with the configuration of ITO/PEDOT：PSS/EL/Cs F/Al.These results indicate that introducing DHTSO unit into polyfluorene backbone could be a promising molecular design strategy for TPA and effective green-light emission.

BLUE LIGHT-EMITTING POLY(FLUORENE-CO-BENZENE) CONTAINING AN OXADIAZOLE MOIETY

A new kind of polyfluorene containing oxadiazole as the side chain was synthesized. The introduction of oxadiazole moiety as more bulky group prevents the aggregation and reduces the crystallinity of the polymers. Efficient intramolecular energy transfer from oxadiazole moiety to the conjugated backbone has been realized, leading to 70% improvement of photoluminescence quantum efficiency of the designed polymers. Compared with PAF, the PFOXD exhibits significant improvement in electroluminescence properties, with luminous efficiency of 0.8 cd/A and maximum luminance of 1800 cd/m2.

Synthesis and properties of polyfluorene copolymers bearing thiophene and porphyrin

To search for more wider absorption and higher charge carriers mobilities materials of polymer solar cell, a series of soluble alternating polyfluorene copolymers were synthesized by palladium-catalyzed Suzuki coupling reaction. Their structures were determined by 1H NMR, IR and UV-vis. And their UV-vis absorption spectra indicated that they had strong absorption over 600 nm spectral range and nearly cover 400-700 nm visible region. The band gaps of copolymers calculated according to cyclic voltammetry （CV） were between 1.96 and 2.03 eV. Polymer：TiO2 bulk-heterojunction films were made from mixtures of polymer and titanium isopropoxide, a precursor for TiO2, via hydrolysis in air overnight. The photoluminescence at 380-800 nm of the blend film of PT-TPP20 （5 mg/mL）：Ti（OC3H7）4 （80 μL/mL） （20% volume fraction） was significantly quenched in the 50% Ti（OC3H7）4 blend film, indicating that rapid and efficient separation of photoinduced electron-hole pairs.

Theoretical Investigation on the Luminescent Properties of Polyfluorene and Poly(fluorene-co-thiophene)

The density functional theory was employed to study the structures, ionization potentials（IPs）, electron affinities（EAs）, and HOMO-LUMO gaps（ΔH-L） of the oligomers. The time-dependent density functional theory（TD-DFT） and ZINDO were employed to study the lowest excitation energies（Egs） and the absorption and emission spectra of the oligomers of polyfluorene（PF） and poly（fluorene-co-thiophene）（PFT）. By extrapolating ΔH-L and Egs to those of infinite chain length, band gaps and effective conjugation lengths of the corresponding polymers were obtained. The IPs, EAs and 2abs of the polymers were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero（I/n=0）. The outcome shows the decreased dihedral angle between fluorene and thiophene units in the PFT compared to that between fluorene units in the PF results in the increased efficient conjugation of PFT. These cause both the maximal absorption and emission wavelengths of PFT red-shifted compared with those of PF.

Synthesis of Polyfluorene-Polytriarylamine Block Copolymer with Emitting Part at Junction Point for Light Emitting Applications

A block copolymer consisting of polyfluorene (PF) and polytriarylamine (PTAA) functionalized with green emitting phenoxazine moiety at the junction point of two blocks was designed and prepared for electroluminescent application. PF homopolymer was synthesized by Suzuki coupling polymerization, and was reacted with brominated phenoxazine. In the presence of the resulting PF functionalized with phenoxazine, C-N coupling polymerization of 4-(4’-bromophenyl)-4’’-butyldiphenylamine was carried out to afford a triblock copolymer, PTAA-phenoxazine-PF-phenoxazine-PTAA (PF-Ph-PTAA). Two types of random copolymers were also synthesized with fluorene and phenoxazine (PF2) by Suzuki coupling polymerization for comparison. All the polymers were soluble in common organic solvents and readily formed thin films by a solution processing. Prepared polymers exhibited similar UV absorption and PL emission in chloroform solutions. In a film state, the existence of phenoxazine unit drastically changed PL spectra. Although the content of phenoxazine unit in PF-Ph-PTAA was relatively high (13 mol%), it showed similar PL spectrum to that of PF2(phenoxazine content, 0.2 mol%) indicating that phenoxazine unit is isolated in single polymer chain nevertheless the high content. EL device based on PF-Ph-PTAA showed green-emission, suggesting that emission sites predominantly located in the vicinity of phenoxazine moiety because of its shallow HOMO level.

The Inorganic-organic Hybrid Junction with n-ZnO Nanorods/p-polyfluorene Structure Grown with Low-temperature Aqueous Chemical Growth Method

The inorganic-organic hybrid junction was synthesized on ITO glass substrate, which was consisted of an n-type ZnO nanorods （NRs） grown by low-temperature aqueous chemical growth method and a p-type polyfluorene （PF） organic film fabricated by spin-coating. The experimental results indicate that densely and uniformly distributed ZnO nanorods are successfully grown on the PF layer. The thickness of the PF layer plays a dominant role for the current-voltage （I-V） characteristic of the ZnO NRs/PF inorganic-organic hybrid junction device, and a p-n junction with obviously rectifying behavior is achieved with optimal PF layer thickness. The photoluminescence （PL） spectrum covering the broad visible range was obtained from the n-ZnO nanorods/p-polyfluorene （PF） structure, which was originated from the combination of the PF-related blue emission and the ZnO-related deep level emission.

An Improved Blue Polymer Light-Emitting Diode by Using Sodium Hydroxide/Ca/Al Cathode

The performance of blue polymer light-emitting diodes （PLEDs） based on poly（9,9-dioctylfluorene） （PFO） is improved by introducing a thin layer of sodium hydroxide （NaOH） between the calcium cathode and the PFO emissive layer. By replacing the commonly used Ca/Al cathode by a NaOH （2.5nm）/Ca （10nm）/Al cathode, the driving voltage is reduced from 8.3 V to 5.4 V and the light-emitting efficiency is enhanced from 0.46cd/A to 0.72cd/A for achieving a luminance of 500cd/m^2, respectively. Moreover, the device with NaOH/Ca/Al cathode shows a pure blue emission of （0.17, 0.12） at high brightnesses. These improvements are attributed to introduction of a thin layer of NaOH that can lower the interracial barrier and facilitate electron injection.

Polyfluorene-Polytriarylamine Block Copolymer as an Additive for Electroluminescent Devices Based on Polymer Blends

Electroluminescent characteristics were investigated for the blue emitting devices fabricated with the blend systems consisting of hole transporting polytriarylamine (PTAA), electron transporting polyfluorene (PF), and a block copolymer with both segments (PF-b-PTAA) as an active layer in order to elucidate the relationship between the chemical nature and morphology of the active layer, and EL performance. The addition of PF-b-PTAA to PF homopolymer afforded the hole injecting and/or electron blocking ability to increase the efficiency. The addition to PF/PTAA blend keeping the chemical composition constant also improved the performance by controlling the morphology and/or the domain size in phase-separated films.

Photocurrent in the Polyfluorene Copolymer/PTCDI Heterojunction Enhanced by Reabsorption of Fluorescence Emission

Copolyfluorenes are of great interest due to their ability to form thin films with tunable optical and electrical properties.In this paper,copolymers of polyfluorene with electron withdrawing dicyanostilbene and dicyanophenanthrene moieties were synthesized;their thin films were characterized by electron spectroscopy,cyclic voltammetry,electrical,and photoelectrical measurements.The mobility of charge carriers in the copolymers was measured for the first time,with the acceptor components providing balanced electron and hole mobilities of the order of 10^(-6) cm^(2)·V^(-1)·s^(-1).Photodetectors based on the copolymer/PTCDI heterojunction exhibited the photoresponse band extended into the green region due to the absorption of PTCDI and an increased photocurrent in the UV-blue absorption band of the copolymer,which is related to the absorption of photoluminescent emission of the copolymers in PTCDI.The presented approach to improving the performance of a polymer-based photodetector is promising in organic optoelectronics.

A Robust and Soluble Nanopolymer Based on Molecular Grid-based Nanomonomer

Shape persistent conformations reduce the complexity of polymer materials. Herein, we propose a concept on the nanopolymer that is a nanoscale polymer chain with the repeat units of nanomonomers, In this article, a soluble organic nanopolymer of wide bandgap semiconductors was synthesized by the Yamamoto polymerization of nanogrid monomer as the repeat units with the rectangle size of -1.7 nm × 1.2 nm. The alkyl side chain substituent at 9-position of fluorenes guarantees the polygrid with excellent solubility. Tetrafluorenes in the conjugation-interrupted backbones of polygrid acts as the active light-emitting centers without obvious green band in the fluorescence spectra of the films after 10 h annealing at 180 ℃, indicating this nanopolymer exhibits excellent spectral stability. Such soluble nanopolymers will be the fifth- generation of macromolecular materials with a potential character of overall performance improvement.

Triazatruxene-containing hyperbranched polymers:Microwave-assisted synthesis and optoelectronic properties

Hyperbranched polymer structures represent a class of high-functionality building blocks with excellent three-dimensional topology for the construction of highly substituted conjugated polymers.In this contribution,an efficient microwave synthesis protocol toward the synthesis of conjugated hyperbranched polymers is presented.A novel series of soluble hyperbranched polyfluorenes (PTF1-PTF3) incorporating triazatruxene moiety as the branch units with various branching degrees have thus been successfully constructed with good yields and high molecular weight via a facile "A2+B2+C3" approach.The structures of the hyperbranched polymers were confirmed by NMR and GPC.Their thermal,optical,and electrochemical properties of the hyperbranched polymers were also investigated.The results showed that introduction of triazatruxene units into the hyperbranched structure endowed the polymer with good thermal stability and highly amorphous properties.Photophysical investigation of PTFx revealed strong blue emission in both solution and solid states.Hyperbranched polymers with higher degree of branching and proper content of linear fluorene units exhibited better photophysical properties in terms of narrow emission spectra and relatively high quantum efficiency as well as improved thermal spectral stability.The triazatruxene branching unit also played a role in raising the HOMO energy levels relative to those of polyfluorenes that would help to improve the charge injection and transport properties.The incorporation of triazatruxene unit into hyperbranched polymers has thus explored an effective avenue for constructing optoelectronic polymers with improved functional characteristics.

Phosphine oxide-functionalized polyfluorene derivatives:Synthesis,photophysics,electrochemical properties,and electroluminescence performance

A series of phosphine oxide-functionalized polyfluorene derivatives,PFH-PO-40-1 (P1),PFH-PO-20-1 (P2),PFH-PO-10-1 (P3),and PFH-PO-1-1 (P4),were prepared via a palladium-mediated Suzuki cross-coupling reaction.The structures and purities of all polymers were fully characterized by 1H and 13C NMR,UV-vis and photoluminescent spectroscopy,gel permeation chromatography,and TGA/DSC.Their emission features showed single broad peaks at about 445 nm in film,compared with those in dilute solutions,which might be caused by some degree of aggregation in the excited states of the backbones.The best electroluminescence (EL) performance of these polymers with configuration of ITO/PEDOT:PSS/Polymer/Alq3/LiF/Al was obtained from P1 (current efficiency was 4.2 Cd/A at 6V).

Electroluminescence performances of 1,1-bis(4-(N,N-dimethylamino)phenyl)-2,3,4,5-tetraphenylsilole based polymers in three cathode architectures

A new silole monomer with two 4-（N,N-dimethylamino）phenyl substitutions on silicon atom as designed and synthesized. Three copolymers PF-N-HPS1, PF-N-HPS10 and PF-N-HPS20 were then obtained by copolymerizations of 2,7-fluorene deriva- tives with the silole monomer at feed ratios of 1%, 10%, and 20%. Their UV-vis absorption, electrochemical, photolumines- cent, and electroluminescent （EL） properties were investigated. PF-N-HPS possessed HOMO levels of -5.25-5.58 eV, and showed green emissions. Using PF-N-HPS as the emissive layer, three different polymer light-emitting diodes were fabricated as device A with ITO/PEDOT/PF-N-HPS/A1, device B with ITO/PEDOT/PF-N-HPS/Ba/A1, and device C with ITO/PEDOT/ PF-N-HPS/TPBI/Ba/A1. For the device A, PF-N-HPS only showed very low EL efficiency of 0.06-0.33 cd/A, indicating that the A1 cathode could not inject electron efficiently to the emissive polymers containing the 4-（N,N-dimethylamino）phenyl groups. For the device B, low work function Ba supplied better electron injections, and the EL efficiency could be improved to 0.85-1.44 cd/A. TPBI with a deep HOMO level of -6.2 eV could enhance electron transport and hole blocking. Thus modi- fied recombinations and largely elevated EL efficiency of 4.56-7.96 cd/A were achieved for the device C. The separation of the emissive layer and metal cathode with the TPBI layer may also suppress exciton quenching at the cathode interface.

Novel Efficient Light-Emitting Polyfluorene Derivatives Modified by Electron-Deficient Moieties with Nonlinear Structure

Two novel fluorene-based copolymers (PFSD and PFMD) containing squaric acid or maleimide unit in the main chain were synthesized in good yields by Suzuki coupling reaction. The resulting polymers possess excellent thermal stability, high electron affinity and high photoluminescence (PL) quantum yields. They can fluoresce in yellow-light range due to either the charge transfer between a fluorene segment and an electron-deficient containing squaric acid/maleimide segment of the polymers or the Forster energy transfer between different polymer chains. The results from PL measurements of the isothermally heated polymer thin films show that the commonly observed aggregate excimer formation in polyfluorenes is very effectively suppressed in these two polymers due to the nonlinear structures of maleimide and squaric acid moieties. Double-layer polymer light-emitting diodes (PLED) were fabricated using the resulting polymers as the emitting layers and Ba or Mg : Ag (V : V= 10 : 1) as cathodes. All the devices show bright yellow emission (562-579 nm) with different maximum external quantum efficiencies (0.006%-1.13%). Compared with the other devices, indium-tin oxide (ITO)/polyethylenedioxythiophene (PEDOT) : polystyrene sulfonic acid (PSS)PFMD/Mg : Ag has the higher maximum external quantum efficiency of 1.13% at 564 cd/m2 with a bias of 8.4 V.

Modification of polyfluorene nanoparticles via inclusion complexa- tion based on cyclodextrin for lectin sensing and cell imaging

Currently, conjugated polymer nanoparticles are widely used with many biological applications, especially bio-imaging and labeling. Thus their modification with different biomacromolecules becomes a crucial step before various applications. In literature,this modification was normally performed via covalent bonds. To our best knowledge, modification based on inclusion complexation has not been reported. Herein, via host-guest interaction between cyclodextrin and adamantane, supramolecular modification to conjugated polyfluorene nanoparticles has been successfully achieved. The glycopolymer-modified conjugated polymer nanoparticles showed excellent binding ability to lectins, such as Galectin-3 and selective imaging behavior to Hep G2 cells.

PURIFIED POLAR POLYFLUORENE FOR LIGHT-EMITTING DIODES AND LIGHT-EMITTING ELECTROCHEMICAL CELLS

Conjugated ployfluorene with 2-（2-（2-methoxyethoxy）ethoxy）ethyl groups （EO-PF） is prepared by the palladium- catalyzed Suzuki coupling reaction. The polymer is purified carefully by a simple chemical procedure. The inductively coupled plasma （ICP） test shows palladium-catalyst in the polymer can be removed by this procedure. The thermal properties, electrochemical properties, UV-Vis absorption properties, photoluminescence properties and electroluminescent properties of the polymer without （EO-PF1） or with purification （EO-PF2） are studied. EO-PF2 shows better PL CIE coordinates in THF solutions as blue light-emitting materials and better photoluminescence stability in thin solid films. Polymer light emitting diodes and electrochemical cells based on EO-PF2 exhibit somewhat improved optoelectronic performance than control devices of EO-PF 1.