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Semi-orthogonal solution processing can circumvent interface intermixing issue of construction of multilayer polymer light-emitting diode devices (PLEDs). In this manuscript, we developed a new strategy to construct multilayer PLEDs by the semi-orthogonal solvents based on the difference between the solubilities of a poly(9,9-dioctylfluorene) that end-capped with a triphenylamine derivative (PFO-TF) (processed with p -xylene) and the light-emitting polymer PPF-SO15 or PPF-SO15-BT1 (processed with 1,4-dioxane). As the highest occupied molecular orbital energy level of PFO-TF (−5.70 eV) lies in between PEDOT:PSS (−5.20 eV) and the light-emitting copolymer PPF-SO15 (−5.94 eV), it can serve as the hole transport layer (HTL) to facilitate hole injection. The blue PLED based on PFO-TF as the HTL exhibits lower turn-on voltage and nearly identical electroluminescent spectra as that of the control device without HTL. Of particular importance is that the blue device with PFO-TF as the HTL exhibits the luminous efficiency over 5.0 cd A −1 , which is much higher than that observed from a device without an HTL (3.51 cd A −1 ) or one with traditional poly(9-vinylcarbazole) as the HTL (4.74 cd A −1 ). Similar trend is also realized for PLEDs based on green-light-emitting polymer PPF-SO15-BT1. These observations indicate that processing of a multilayer device with this specific semi-orthogonal system may be a promising strategy for the construction of efficient PLEDs. [ABSTRACT FROM AUTHOR]

In this manuscript, we introduced an effective strategy to improve the electroluminescent performance of poly[(fluorene)- co -dibenzothiophene- S , S -dioxide]s (PFSO) derivatives by end-capping, which was carried out by introducing N -([1,1'-biphenyl]-4-yl)- N -(4-phenyl)-9,9-dimethyl-9 H -fluoren-2-amine moiety (TF) at the end of the polymerisation. Compared with the pristine copolymer PFSO that end-capped by phenyl unit, the TF-end-capped copolymers exhibit improved highest occupied molecular orbital levels, which can facilitate hole injection and thus lead to more balanced charge carrier transport in the emissive layer. Of particular importance is that the resulting copolymers can be used to fabricate single-layer devices without hole transport layer, which dramatically reduced driving voltage and obviously increased luminous efficiency relative to device fabricated from the copolymer PFSO that end-capped by phenyl unit. The best performance is obtained from device based on PFSO-TF16, which exhibits an unprecedented turn-on voltage of 2.7 V and a maximum luminous efficiency of 4.45 cd A −1 , with CIE coordinates of (0.15, 0.13). These results demonstrate that our end-capping strategy has great potential for the development of highly efficient blue light-emitting polymers for single-layer light-emitting devices. [ABSTRACT FROM AUTHOR]

Abstract Two series of twisted bipolar poly(2,7-carbazole) derivatives, namely PCz-37RSOs and PCz-28SOs, were synthesized by introducing electron-deficient 2,8-dioctyl- dibenzothiophene- S,S -dioxide-3,7-diyl (37RSO) and dibenzothiophene- S,S – dioxide −2,8-diyl (28SO) unit into poly(9-heptadecanyl-2,7-carbazole) (PCz) backbone, respectively. The incorporation of electron-withdrawing 37RSO and 28SO into PCz backbone decreased effective conjugation length, and further restrained charge transfer effect existed in dipolar system, simultaneously, the balanced charge carrier injection/transportation were realized due to the eletrophilicity of SO unit. Consequently, the resulting polymers showed hypsochromic shift and narrowed emission spectra regarding to PCz-37SOs that contains linear SO unit in main chain, and exhibited balanced hole/electron fluxes with respect to PCz in the range of 0–10 V. The single-layer devices based on resulting bipolar polymers exhibited excellent electroluminescent spectra stability in the current densities from 100 to 400 mA cm−2, and displayed deep blue electroluminescence spectra with the Commission Internationale de L' Eclairage (CIE) of (0.16, 0.07) for PCz-37RSO5 and (0.16, 0.09) for PCz-28SO5. The superior device performance was achieved with the maximum luminous efficiency (LE max) of 2.69 cd A−1 for PCz-28SO20 , which obviously outperformed that of 0.24 cd A−1 for PCz. These results indicated that twisted molecular structure design is a promising strategy for efficient deep blue light-emitting polymers. Graphical abstract Image 1 Highlights • Two series of twisted bipolar poly(2,7-carbazole) derivatives were designed and synthesized. • Twisted structure greatly decreases intramolecular charge transfer and results in the deep blue emission with CIE y < 0.1. • PCz-28SO20 exhibits a maximum luminous efficiency of 2.69 cd A−1, which obviously outperforms that of 0.24 cd A−1 for PCz. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of a thermally crosslinkable hole-transporting poly(indenofluorene- co -triphenylamine) copolymer (X-IFTPA) containing a vinyl-functionalized triphenylamine moiety. This copolymer exhibited an exothermal peak at 125 °C in the first heating/cooling cycle of a differential scanning calorimetry study, indicating that crosslinking occurred. The highest occupied molecular orbital energy level of this copolymer was estimated to be −5.30 eV, as determined by cyclic voltammetry measurement. Flat and uniform films were formed by spin casting X-IFTPA from chlorobenzene solution. Crosslinking can be finished by thermally annealing the film at 150 °C for 24 min, which can be confirmed by reflectance Fourier transform infrared spectroscopy and UV–Vis absorption spectra. Multi-layer polymer light-emitting diodes (PLEDs) incorporating X-IFTPA as the hole transport layer and a green-light-emitting copolymer as the emissive layer exhibited enhanced luminous efficiency relative to that of a control device without a hole transport layer. Thus, the developed cross-linkable copolymer X-IFTPA is a promising material for the construction of efficient PLEDs. [ABSTRACT FROM AUTHOR]

Efficient blue polyfluorenes have been generated by incorporating the hole transport material N -([1,1′-biphenyl]-4-yl)-9,9-dimethyl- N -(4-(9-phenyl-9 H -carbazol-3-yl)- phenyl)-9 H -fluoren-2-amine (BCFN) into poly(9,9-dioctylfluorene) (PFO) as an emissive layer. BCFN has an appropriate highest occupied molecular orbital (HOMO) energy level and high hole transport/electron barrier properties, which can effectively reduce the hole injection barrier and improve the charge carrier injection and transport. These properties resulted in a significant improvement in the electroluminescent (EL) performance of PFO. To further improve the EL performance of PFO, the blend hole transport layer, PVK [Poly(N-vinylcarbazole)]:BCFN with weight ratio of 3:7, was inserted between the PEDOT:PSS and the emissive layer. The blend hole transport layer effectively reduced exciton quenching and markedly decreased the hole injected barrier. A maximum luminous efficiency ( LE max ) of 4.31 cd A −1 was obtained with the CIE coordinates of (0.17, 0.13). The device maintained a LE max of 4.27 cd A −1 at a luminance of 1000 cd m −2 . In addition, stable EL spectra were obtained and were nearly identical when the applied voltage was increased from 5 to 11 V. These results indicate that blending the appropriate hole transport material can be an efficient method to improve device performance based on the large band gap of blue-lighting materials. [ABSTRACT FROM AUTHOR]

Two novel polyfluorene-based blue-light emitting copolymers consisting of aromatic carbazole or dibenzothiophene- S , S -dioxide (SO) moiety in side chain are designed and synthesized based on a palladium-catalyzed Suzuki polymerization. The UV–vis absorption, photoluminescence characteristics and wide-angle X-ray diffraction measurements of the resulting copolymers demonstrate that the incorporation of such aromatic units can induce the formation of the β -phase. The resulting copolymers consisting of aromatic units exhibit improved electroluminescence properties relative to the pristine PFO film. A maximum luminous efficiency of 2.25 cd A −1 with Commission Internationale de l’Eclairage coordinates of (0.17, 0.09) is obtained from the light-emitting device based on the copolymer consisting of SO unit (PFO-SO). Device based on copolymer PFO-SO also exhibits stable electroluminescent spectra and relatively low roll-off of luminous efficiency at high current densities. These observations indicate that the incorporation of aromatic moiety in side chain is a promising strategy to obtain stable blue-light-emitting polyfluorenes with enhanced efficiency. [ABSTRACT FROM AUTHOR]

Deep blue small-molecule organic light-emitting diodes (OLEDs) play an important role in full-color flat panel displays and solid-state lighting. Here, a series of luminogens (BM1−BM4) are developed and constituted of methyl-modified dibenzothiophene- S,S -dioxide (SO) with different linking patterns and fluorene unit with grafted carbazole-functionalized side chains. The linking position of SO unit largely affects the conjugation degree, band gap, molecular geometry, and electron cloud distribution of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which ultimately regulates the electroluminescence performance of OLED devices. Besides, the functionalized methyl substitutions endow all luminogens with relatively large torsion angles. Hence, they present a peak wavelength (λ PL) of 423–439 nm in the film states, which renders them as appealing deep blue emitters. Apart from BM1 because of excimers, single-layer OLED devices based on BM2−4 displayed typical deep-blue emissions in the wavelength range of 426–438 nm, furthermore, the optimized multilayer non-doped devices adopting PFN as an electron injection layer yield a decent maximum luminous efficiency (LE max) of 4.33 cd A−1, and Commission Internationale de l'Eclairage (CIE) coordinates of (0.16, 0.11) due to the more balanced hole and electron fluxes. [Display omitted] • Small molecules with methyl-substituted dibenzothiophene- S,S -dioxide unit as core and fluorene unit with grafted carbazole-functionalized side chains are synthesized. • The meta- or para-position of dibenzothiophene- S,S -dioxide unit and the effective conjugation length of all luminogens have significant influence on the photophysical, electronchemical, and electroluminescent properties. • The BM4 OLEDs device exhibits a maximum luminous efficiency of 4.33 cd A−1 with CIE coordinates of (0.16, 0.11). [ABSTRACT FROM AUTHOR]

Two efficient solution-processable orange Ir(III) complexes were developed based on the classical orange phosphorescent dye Ir(phq) 3 . The indenocarbazole and bipolar triazine-indenocarbazole moieties introduced into IrO1 and IrO2, respectively, afforded good solubility (>10 mg mL −1 ) in chlorobenzene, making these emitters suitable for the fabrication of solution-processed devices. The obtained devices based on IrO1 with 4,4ʹ-bis(carbazol-9-yl)biphenyl as the host material displayed a maximum luminance efficiency of 45.8 cd/A with CIE coordinates of (0.55, 0.45). The devices based on IrO2 exhibited a redshift of the spectrum relative to Ir(phq) 3 and displayed a maximum luminous efficiency of 27.0 cd/A with CIE coordinates of (0.59, 0.41). To the best of our knowledge, these are the highest performances reported to date for solution-processed Ir(phq) 3 -based light-emitting devices. These excellent performances demonstrate that IrO1 and IrO2 are promising candidates for high-performance orange phosphorescent organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

We designed and synthesized a novel sky-blue fluorescent dye, 7,7,13,13-tetramethyl- N 5 ,N 5 ,N 11 ,N 11 -tetra- p -tolyl-7,13-dihydrobenzo[ g ]indeno[1,2- b ]fluorene-5,11-diamine (DANIF), which contains a naphthalene indenofluorene (NIF) core and two diphenylamine end-capped groups. Because of the presence of steric diphenylamine terminal groups, DANIF showed a high glass transition temperature ( T g ) of 161 °C and decomposition temperature (5% weight loss temperature) of 390 °C, which is suitable for the evaporation process. With 9,10-di(2-naphthyl)anthracene as the host and DANIF as the emitter, the fabricated vacuum-deposited organic light-emitting diodes exhibited a relatively low turn-on voltage of 2.8 V and a maximum luminous efficiency of 11.0 cd A −1 . The Commission Internationale de l’Eclairage coordinates of (0.15, 0.22) were achieved with a DANIF weight ratio of 7%. The combination of low driving voltage and high efficiency of the device gave rise to an impressive operational lifetime of 160 h (initial at 1000 cd m −2 , decay to 85% of the initial luminance). These results indicate that DANIF is a promising candidate for the development of highly efficient blue organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

Blue light-emitting polymers were synthesized by Suzuki polycondensation via introducing N -(2-decyltetradecyl)carbazole[2,3- b benzo d thiophene- S,S -dioxide (BTOCz) unit into the polyfluorene and polycarbazole backbone, respectively. The resulting polymers showed high thermal stability with the decomposition temperatures over 410 °C and the glass transition temperatures up to 180 °C with the increase of BTOCz content in the polymers. The lowest unoccupied molecular orbitals energy level significantly decreased, and the highest occupied molecular orbitals energy level were almost unchanged with the increasing content of BTOCz unit in the polymers. The photoluminescence quantum yields of PF-BTOCzs and PCz-BTOCzs are 45–59% and 41–54%, respectively. The device performances based on the polymers exhibited stable electroluminescent spectra with the variation of applied current densities from 100 mA cm−2 to 500 mA cm−2. The peak luminous efficiencies of 6.36 cd A−1 and 6.25 cd A−1, and the peak external quantum efficiencies of 5.03% and 4.39% with the Commission Internationale de L'Éclairage coordinates of (0.16, 0.21) and (0.17, 0.26) were obtained for PF-BTOCz30 and PCz-BTOCz30, respectively, at a turn-on voltage of 3.0 V and 2.8 V based on a single-layer device configuration of ITO/PEDOT:PSS/Emissive layer/CsF/Al. The results indicated that the strategy of introducing ambipolar BTOCz unit into the polyfluorene or polycarbazole backbone to construct the twisted molecular structure has a great potential for the development of highly efficient blue light emission. Image 1 • The faintly twisted blue light-emitting polymers were synthesized. • The incorporation of BTOCz unit can improve the device performances. • A single-layer device exhibited LE max of 6.36 cd/A at a turn-on voltage of 3.0 V. [ABSTRACT FROM AUTHOR]