Zhenghuan Lin

Nondoped Pure-Blue OLEDs Based on Amorphous Phenylenevinylene-Functionalized Twisted Bimesitylenes

The twisted bimesitylene scaffold hinders crystallization and imparts amorphous nature to the oligophenylenevinylenes (OPVs) generated by 2- and/or 4-fold functionalization. The resultant phenylenevinylenes 1-5 with unique molecular topology exhibit excellent thermal and solid-state luminescence properties. The amorphous nature permits their application as pure-blue emissive materials in OLEDs. Under nondoped conditions, the device performances observed surpass those for analogous and simple oligophenylenevinylenes known so far; for example, the device based on OPV 2 as an emitting material and structurally analogous Bim-DPAB as a hole-transporting material yields pure-blue electroluminescence with an external quantum efficiency of ca. 4.70% at 20 mA/cm(2), which is higher than those reported for nondoped pure-blue OPV emitters.

A Λ-shaped donor–π–acceptor–π–donor molecule with AIEE and CIEE activity and sequential logic gate behaviour

A novel Λ-shaped donor–π–acceptor–π–donor molecule BCPMM with AIEE, CIEE and polymorphism-dependent fluorescence properties was developed. The emission of BCPMM in solid states could be tuned by an external stimulus, which was utilized to construct five simple logic gates and more than ten kinds of sequential combinational logic systems.

Polymorphism-dependent fluorescence of bisthienylmaleimide with different responses to mechanical crushing and grinding pressure

A herringbone structured compound, 3,4-bisthienylmaleimide (BTM), with reversible four-color and on/off switching upon external stimuli is reported here. Three kinds of BTM crystals with strong red (RC), orange (OC) and yellow (YC) fluorescence, as well as a brown solid (BS) with weak orange luminescence are obtained in the experiments. Heating, solvent vapor and pressure, including crushing and grinding, can reversibly switch BTMs emission between RC, OC, YC and BS. Base vapor (NEt3)-heating cycle treatment of BTM film in polystyrene can induce emission switching between bright/dark (on/off) states. The results of crystal structural analysis and photophysical property studies demonstrate that although OC and YC have the same crystal structure, they exhibit different fluorescent properties, due to their different surface structures. Heat induces metastable RC, with orderly π-stacking, to turn into stable OC or YC, with brick stone stacking. Crushing can damage the surface structure of OC and transform it into YC without altering the crystal structure. Grinding OC or YC destroys the orderly stacking to yield amorphous BS.

White light-emitting devices with a single emitting layer based on bisindolylmaleimide fluorophores

A series of bisindolylmaleimide dyes (1–3) were synthesized and they exhibited intensive orange to red color luminance deriving from charge transfer transitions. Highly efficient light-emitting devices were fabricated using these materials as emitters by doping 1% in a tris(8-hydroxyquinolinato)aluminium (Alq3) host, which performed in a quantum efficiency of ∼4% with a maximal intensity >40 000 cd/m2. Broad band white emission can be produced by combining their reddish color with another blue emitter. While doped in 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) in suitable concentrations, dual emission was obtained from a single layer. The device with configuration ITO/PEDOT:PSS/dye 1 (1%):NPB/TPBI/LiF/Al yielded white light with maximum luminance efficiency of 6.6 cd/A, power efficiency of 6.4 lm/W and quantum efficiency of 2.6%, where PEDOT:PSS is poly(ethylenedioxythiophene):poly(styrenesulfonic acid), and TPBI is 2,2′,2″-(1,3,5-benzentriyl)tris(1-phenyl-1H-benzimidazole). This device can be turned on at a low voltage (<3 V) and emits a white color with CIE coordinate (0.32, 0.34), which stays invariant over a wide range of applied voltage.

Diarylmaleic anhydrides: unusual organic luminescence, multi-stimuli response and photochromism

Diarylmaleic anhydride derivatives containing benzene (BPMA), thiophene (BTMA) and indole (BIMA) exhibit diverse and distinct fluorescence: aggregation-caused quenching (ACQ) of red emission of BIMA, blue aggregation-induced emission (AIE) of BPMA, and green dual-state emission (DSE) of BTMA in both solution and the solid state. Theoretical calculation and crystal structure analysis indicate that intramolecular and intermolecular interactions are responsible for their different emission behavior. A series of DSE-active molecules with full-color emission could be developed for the first time, through modification of the structures of BPMA and BIMA. Interestingly, BTMA and BPMA display multi-stimuli-responsive luminescence with a high-contrast (Δλem > 100 nm) and an unusual photochromic phenomenon in dichloromethane, which were utilized to construct rewritable data storage and mimic molecular logic operation (4-to-2 encoder and 1 : 2 demultiplexer), respectively.

A facile one-pot synthesis of hyper-branched carbazole-based polymer as a hole-transporting material for perovskite solar cells

A low-cost, hyper-branched, carbazole-based polymer (HB-Cz) was designed and synthesized by a facile “A3 + B2” one-pot Suzuki polycondensation reaction. Due to the hyper-branched structure and carbazole unit, HB-Cz is a promising candidate for a hole-transporting material, which was confirmed in perovskite solar cells (PVSCs) with a configuration of ITO/TiO2/MAPbI3/HB-Cz/Ag. The films of poly-(3-hexylthiophene) and linear poly[N-(1-octylnonyl)-9H-carbazole-2,7-diyl] were also used as hole-transporting layers (HTLs) in the reference devices. Time-resolved photoluminescence spectra indicate that HB-Cz has the fastest charge regeneration. Electrochemical impedance spectroscopy revealed that HB-Cz could reduce carrier recombination effectively, improving the open circuit voltage and fill factor of the PVSCs. A PCE of 14.07% obtained from the HB-Cz-based device was much higher than those of devices based on P3HT (9.05%) and PCz (6.60%), and this is attributed to the superior hole-transporting property and surface smoothing effect of the HB-Cz HTL.

Diarylmaleimide fluorophores: intensely emissive low-band-gap guest for single white polymers with highly efficient electroluminescence

A series of novel single white polymers, PFPMs and PFTMs, were designed and synthesized by introducing a green diphenylmaleimide (PM, λem = 500 nm) or yellow dithienylmaleimide (TM, λem = 557 nm) fluorophore guest into a blue polyfluorene (PF) host. By adjusting the feed ratio of the maleimide unit and fluorene unit, the resulting single white polymers exhibited a dual emission, including blue emission (415/439 nm) from PF and yellow (546 nm) or red (659 nm) emission from the PM or TM guest. The large red-shift in emission of the PM and TM in the backbone of the polymers originates from their conjugated structure being extended by the fluorene units. All the polymers show similar and high thermal stability and large solubility in common organic solvents. Their electroluminescent properties were investigated in single-emitting-layer devices fabricated by a solution process with the configuration of ITO/PEDOT:PSS/polymer/TPBI/LiF/Al. PFPM03, containing 0.3% PM, exhibited an excellent white electroluminescent performance for the effective and incomplete energy transfer from the PF host to the maleimide guest. The white device based on annealed PFPM03 at 140 °C for 30 min could be further improved to reach a maximal current efficiency of 8.14 cd A−1, power efficiency of 3.93 lm W−1, and external quantum efficiency of 3.78% with CIE coordinates of (0.34, 0.41).

Solvent-dependent and highly selective anion sensing and molecular logic application of bisindolylmaleimide derivatives

A series of bisindolylmaleimide dyes (IMs) with different N-substituents (IM-PFB, IM-TBA and IM-MB) and planarity (IMC-MB and IM-MB) were designed and synthesized to detect anions selectively and sensitively. The anion-sensing properties were investigated systematically by changing the N-substituents of maleimide, solvent type and molecular planarity. Results indicate that the anion recognition is significantly affected by the solvent type rather than the N-substituents. Different anion sensitivity in various solvents makes IMs selectively detect F− in ACN, H2PO4− in DCM and CN− in THF. Due to the fixed location of two NH groups, the dye IMC-MB with planar structure exhibits poor sensing selectivity in various solvents. The titration curves of anions show that the sensing mechanism of IMs in various solvents for anions is different. The further experimental and DFT/TDDFT calculation results demonstrate that the hydrogen bond interaction and deprotonation of one H atom take place in DCM and THF, respectively, and that the two interactions synchronously exist in ACN. Interestingly, the solvent-dependent anion recognition can make IM-PFB mimic the function of three kinds of decoders (1-to-2, 2-to-3 and 2-to-4), a 4-to-2 encoder and a 1 : 2 demultiplexer. It is really rare for one molecule to mimic so many logic operations.

Highly efficient white electroluminescence from dual-core star-shaped single polymer: performance improved by changing the non-emissive core

Two series of dual-core star-shaped polyfluorenes (DC-TPAs and DC-SBFs) based on a small quantity of green-emitting phenylmaleimide cores and a good deal of non-emissive cores were prepared by a one-pot Suzuki reaction. Triphenylamine (TPA) and 9,9-spirobifluorene (SBF) are employed as the non-emissive cores to construct DC-SBFs and DC-TPAs, respectively. Due to the π-conjugation extended by the fluorene units, the phenylmaleimide core displays a yellow emission which contributes to the white emission with the blue-emitting polyfluorene arms. DC-SBFs with four arms exhibit a better protection for emissive cores and a higher energy transfer efficiency than DC-TPAs with three arms. Consequently, the quantum yield of white emission of the polymers in the film was improved by changing TPA into SBF as the non-emissive core, reaching 0.80 for DC-SBF03. Additionally, the electrons and holes can be transported smoothly in DC-SBFs. A very high electroluminescent efficiency was obtained for DC-SBF03 with a maximum luminous efficiency of 17.4 cd A−1, power efficiency of 10.9 lm W−1 and external quantum efficiency of 6.2% when applied in the solution-processing white polymeric light-emitting devices (WPLEDs) with a LiF/Al cathode. The results denote that the non-emissive core plays a key role in the performance of the star-shaped single white polymers. It provides another way to improve the efficiencies of WPLEDs by designing simple non-emissive cores of the dual-core polymers, and avoiding the complicated synthesis of fluorophores.

Macroreticular Polystyrene Hybridized Resins with Both Perfluoroalkanesulfonic and Carboxylic Functional Groups

Macroreticular polystyrene hybridized resins (FPSA) with both perfluoroalkanesulfonic and carboxylic functional groups have been synthesized at mild conditions by following suspension polymerization, perfluoroalkylation by ω-fluorosulfonylperfluorodiacyl peroxides (SFAP), alkali hydrolysis and acidification. The hybridized resins were characterized by FTIR, TGA, acidimetry and nitrogen sorption technique. The influences of the crosslink degree, the chain length and amount of SFAP on the resin’s properties were also investigated. FPSA exhibited higher exchange capacity and surface area than Nafion NR 50 and better thermostability than Amberlyst 15.