Juan Song

The synthesis of shape-controlled α-MoO3/graphene nanocomposites for high performance supercapacitors

Novel nanoflake-like and nanobelt-like α-MoO3/graphene nanocomposites were synthesized by a facile hydrothermal method through tailoring the content of Mo source. The formation mechanisms of α-MoO3/graphene nanocomposites with different morphologies has been investigated. As a model, the α-MoO3/graphene nanocomposites were studied for electrochemical energy storage supercapacitor devices. The results showed that α-MoO3 nanoflakes/graphene displayed better supercapacitive performances than that of α-MoO3 nanobelts/graphene, arising from the structural superiority and optimum compositions. The best composite exhibited a high specific capacitance (up to 360 F g−1) at a current density of 0.2 A g−1, good rate capability, and a nearly 100% long-term cycle stability. This study provided a facile and optimal experimental design to prepare α-MoO3/graphene composite materials which act as promising electrode materials for high-performance supercapacitors.

Synthesis of Fluoren-9-ones and Ladder-Type Oligo-p-phenylene Cores via Pd-Catalyzed Carbonylative Multiple C–C Bond Formation

A new route to various substituted fluoren-9-ones has been developed via an efficient Pd-catalyzed carbonylative multiple C-C bond formation. Under a CO atmosphere, using commercially available aryl halides and arylboronic acids as substrates, this three-component reaction proceeded smoothly in moderate to excellent yields with good functional-group compatibility. The mechanistic investigations suggested a sequential process for the reaction that forms o-bromobiaryls in the first stage followed by a cyclocarbonylation reaction. This chemistry has been successfully extended to construct ladder-type oligo-p-phenylene cores.

Efficient palladium-catalyzed C(sp2)–H activation towards the synthesis of fluorenes

A facile protocol for the synthesis of fluorene derivatives has been developed through palladium-catalyzed cyclization of 2′-halo-diarylmethanes via activation of arylic C–H bonds. The reactions occurred smoothly and allowed both electron-rich and electron-deficient substrates to convert into their corresponding fluorenes in good to excellent yields. Studies revealed that this Pd-catalyzed cyclization was also available for the substrates of 2′-chloro-diarylmethanes and no catalyst poisoning occurred for 2′-iodo-diphenylmethane.

Design of C^NN type iridium(III) complexes towards short-wavelength emission for high efficiency organic light-emitting diodes

In this paper, by introducing the strong electron-withdrawing moiety of difluoropyridinyl to the C^NN type main-ligand, and combining a trifluoromethylated-triazole (fptz) or a picolinate (pic) as the ancillary ligand, we have synthesized two new iridium(III) complexes with blue emission, i.e., iridium(III) bis[3-methyl-6-(2′,4′-difluoro-pyridinato)pyridazine] trifluoromethylated-triazole (1) and iridium(III) bis[3-methyl-6-(2′,4′-difluoro-pyridinato)pyridazine] picolinate (2). These are the first C^NN type iridium(III) complexes with an emission wavelength shorter than 500 nm. In particular, with the increased electron withdrawing property from the ancillary ligand of fptz, the emission from 1 is more blue. Additionally, based on quantum chemistry calculations, it was found that, different from the general case of the main-ligand and Ir-atom distribution, the electrons of the highest occupied molecular orbital (HOMO) also partially locate at the ancillary ligand with very strong electron withdrawing properties. This phenomena is seldom reported in the literature. Organic light-emitting diodes with 1 or 2 as a dopant have been fabricated. High efficiencies of 41.6 cd A−1 (20.1%) with sky-blue emission and 62.8 cd A−1 (26.5%) with blue-green emission were obtained. These are the first blue electroluminescent materials based on iridium complexes with a C^NN type ligand so far.

Facile synthesis and optoelectronic properties of N,N-difluorenevinylaniline-based molecules

A series of RGB molecules (FXs) with a tuneable light-emitting core and difluorenylamino-based peripheries were synthesized through the Heck coupling reaction in good yields. The intramolecular energy transfers and antenna effects were verified in this series of compounds. Strong photoluminescence (PL) from deep blue (∼415 nm) to saturated red (∼645 nm) was observed. The FXs exhibit good solubility and stability, high fluorescence quantum efficiency (up to 93% in THF and 73% in film), short lifetime (1.3–2.6 ns), and high charge injection and transport properties, revealed by both experimental measurements and theoretical calculations. The preliminary organic light-emitting diode devices exhibit only slightly blue-shifted electroluminescence in comparison with PL without stack characters. This full-colour emitting and solution-processable D–π-X–π-D star-burst molecules are highly attractive for organic optoelectronics.

Novel phosphorescent iridium(III) complexes containing 2-thienyl quinazoline ligands: synthesis, photophysical properties and theoretical calculations

The easy tailoring of organic ligands of iridium(III) complexes provides a facile way to tune their opto-electronic properties for applications in high efficiency phosphorescent light emitting diodes. Herein, a series of yellow and red emitting phosphorescent iridium complexes based on 2-thienyl quinazoline derivatives are successfully synthesized and systematically characterized with various opto-electronic properties. The X-ray crystal structures demonstrate that the iridium centers in the complexes with bulky substituents on the 4-position of quinazolyl rings prefer to chelate with the N atoms in the 1-position of quinazolyl rings. Both experiment and theoretical studies indicate that the steric hindrance along with the electron-donating effect of substituents on the C^N ligands enhances the emission quantum yields, accompanied by significant emission shifts. Two yellow phosphorescent iridium complexes (Ir2 and Ir3) are successfully designed and exhibit moderate emission efficiencies, through the incorporation of bulky ligands with strong electron-donating abilities (piperidine for Ir2 and 2,6-dimethyl-phenoxy for Ir3, respectively). The synergistic effect of electron structure and hindrance of ligand is believed to be a promising strategy for tuning the opto-electronic properties of iridium complexes.

Pure aromatic hydrocarbons with meta-linked phenyl-core and perihedral fluorene substitutions with/without inert groups of tert-butyl: bipolar hosts for blue phosphorescence

Two pure hydrocarbon molecules of 1,3,5-tris(9-phenyl-9H-fluoren-9-yl)benzene (mTPFB) and 1,3,5-tris(2-tert-butyl-9-phenyl-9H-fluoren-9-yl)benzene (tBu-mTPFB) were synthesized. Due to the conjugation blocked connection mode and rigid/bulky substitutions, these two materials possess high triplet energy, enabling them as good hosts for blue phosphor in PhOLEDs. By studying their thermal, electrochemical, electronic absorption and photoluminescent properties, it was found that the influence of the inert tert-butyl group on material photoelectrical properties is negligible. For instance, mTPFB and tBu-mTPFB showed very similar absorption and emission profiles, with almost the same bandgap, triplet energy and energy levels. However, the encapsulation of tert-butyl on the 2-position of 9-phenylfluorene enhanced material thermal stability. Most importantly, carrier transport properties were improved dramatically, as proved by the mono carrier device. Blue phosphorescent OLEDs hosted by tBu-mTPFB showed external quantum efficiency of 15.2% and current efficiency of 23.0 cd/A, which were much higher than that of the OLEDs based on mTPFB with the analogous structure.