b S Supporting Information ' INTRODUCTIONSynthesis and properties of functional branched and star polymers have attracted much attention since these polymers usually possess unique physicochemical properties and wide applications originating from a large number of chain ends per molecule and their branched chain architectures. Generally, hyperbranched polymers can be synthesized by step-growth polymerization via polycondensation or addition polymerization of multifunctional monomers, 3,4,30-32 copolymerization of conventional monomers via self-condensing vinyl polymerization (SCVP), 33-37 or copolymerization of vinyl monomers in the presence of multifunctional vinyl comonomers. 38,39 "Living"/ controlled radical polymerization approaches such as inifertermediated polymerization, 40 nitroxide-mediated polymerization, 41 atom transfer radical polymerization, 42-44 and reversible addition-fragmentation chain transfer (RAFT) polymerization [45][46][47][48][49][50][51][52][53] have been efficiently used to synthesize a variety of hyperbranched and star polymers with controlled compositions and variable functionality. Among them, RAFT polymerization is a facile and versatile approach to synthesize hyperbranched and star polymers due to its many advantages such as relatively mild reactions, wide range of monomers, tolerance of various functionalities, and lack of metal catalyst. A range of hyperbranched polymers have been achieved by RAFT polymerization in the presence of divinyl comonomers, 38,39 from a polymer backbone with pendant xanthate groups, 54 or with AB* styryl or acryloyl chain transfer agents. 55-58 Until now, the types of hyperbranched polymers obtained via RAFT process were relatively limited, and the feed ratio of vinyl monomer to chain transfer agent was usually higher than 10. In particular, the copolymerization behavior of conventional monomer with polymerizable RAFT agent has not been thoroughly investigated. It is therefore of great interest to study in depth the dependence of copolymer composition and degree of branching (DB) of hyperbranched copolymers on reaction conditions during RAFT polymerization.Star polymers, on the other hand, have been well-studied. They can be synthesized by approaches such as "arm first", 59-63 "core first", 64-67 and their combination. [68][69][70][71] The arm first approach involves the synthesis of prefabricated arms, usually through "living"/controlled polymerization, followed by reaction with a multifunctional core reagent, which is easily performed and can also afford target star polymers with low polydispersity. The potential drawback of arm first method is that the arm ABSTRACT: Facile synthesis of hyperbranched and star polymers on the basis of S-(4-vinyl)benzyl S 0 -propyltrithiocarbonate (VBPT) was described. RAFT copolymerization of VBPT with vinyl monomers such as methyl methacrylates (MMA), styrene (St), methyl acrylate (MA), and tert-butyl acrylate (tBA) afforded hyperbranched copolymers with variable branch length and degree of branching. Hyperbranched ...
Collaborative filtering (CF) recommenders based on User-Item rating matrix as explicitly obtained from end users have recently appeared promising in recommender systems. However, User-Item rating matrix is not always available or very sparse in some web applications, which has critical impact to the application of CF recommenders. In this article we aim to enhance the online recommender system by fusing virtual ratings as derived from user reviews. Specifically, taking into account of Chinese reviews' characteristics, we propose to fuse the self-supervised emotion-integrated sentiment classification results into CF recommenders, by which the User-Item Rating Matrix can be inferred by decomposing item reviews that users gave to the items. The main advantage of this approach is that it can extend CF recommenders to some web applications without user rating information. In the experiments, we have first identified the self-supervised sentiment classification's higher precision and recall by comparing it with traditional classification methods. Furthermore, the classification results, as behaving as virtual ratings, were incorporated into both user-based and item-based CF algorithms. We have also conducted an experiment to evaluate the proximity between the virtual and real ratings and clarified the effectiveness of the virtual ratings. The experimental results demonstrated the significant impact of virtual ratings on increasing system's recommendation accuracy in different data conditions (i.e., conditions with real ratings and without).
Recent studies on electrophosphorescent polymeric devices have demonstrated that charge‐trapping‐induced direct recombination on the phosphorescent dopant is of crucial importance. In this paper, we show that the electrochemical properties of phosphorescent molecules, which reflect their carrier‐trapping ability, may be a basic design criterion for the selection of host and device configuration. The systems, consisting of a red phosphorescent [Ru(4,7‐Ph2‐phen)3]2+ dopant and two blue hosts 2‐biphenyl‐4‐yl‐5‐(4‐tert‐butyl‐phenyl)‐[1,3,4]oxadiazole (PBD) and poly(vinylcarbazole) (PVK), are intensively studied. The triplet energy level of PVK and PBD is higher than that of the [Ru(4,7‐Ph2‐phen)3]2+, and both hosts show the ability of efficient energy transfer to the dopant, however, efficient electroluminescence (EL) is only obtained in the PVK‐host system. The combined studies of photoluminescence (PL), EL, and electrochemistry for doped films demonstrate that [Ru(4,7‐Ph2‐phen)3]2+, which undergoes a multielectron trapping process as it is used as a dopant in electron‐rich (n‐type) hosts, for instance, PBD, may induce an inefficient recombination for the resulting emission. Whereas using a hole‐rich (p‐type) polymer, such as PVK, as a host and inserting both hole‐blocking and electron‐transfer layers can effectively increase the efficiency of the corresponding devices up to 8.63 Cd A–1, because of the reduced probability of multielectron trapping at the [Ru(4,7‐Ph2‐phen)3]2+ sites.
Red electrophosphorescence from light-emitting devices based on ruthenium(II)-complex [Ru(4,7-Ph2-phen)3]2+-doped wide-band-gap semiconductive polymers, i.e., poly(vinylcarbazole) (PVK), polydihexylfluorene (PDHF), and ladderlike polyphenylene (LPPP), as the emitting layers are reported. However, only highly efficient energy transfer was investigated in a PVK system, not only because of the relatively longer lifetime of its excited state compared with PDHF and LPPP, but also because of the good chemical compatibility of [Ru(4,7-Ph2-phen)3]2+ with PVK. The EL spectra show the characteristic spectrum of [Ru(4,7-Ph2-phen)3]2+, at a peak of 612 nm and Commission Internationale del’Eclairage of (0.62, 0.37). The optimized device indium tin oxide/PVK: 5 wt % [Ru(4,7-Ph2-phen)3]2+/PBD/Alq3/LiF/Al shows the maximum luminance efficiency and power efficiency as 8.6 cd/A and 2.1 lm/W, respectively.
The mixed-ligand polypyridine ruthenium(II) complexes, [Ru(bpy)(2)(dmeb)](2+)(PF(6)(-))(2) (Ru(dmeb)(2+)) and [Ru(bpy)(2)(dbeb)](2+)(PF(6)(-))(2) (Ru(dbeb)(2+)), where bpy is bipyridine, dmeb is 4,4'-dimethyl ester-2,2'-bipyridine, and dbeb is 4,4'-dibutyl ester-2,2'-bipyridine, are synthesized and characterized, and their spectroscopic, electrochemical, and electroluminescent properties are reported. Both Ru(II) complexes showed strong emission from the triplet metal-to-ligand charge-transfer excited state, red-shifted emission spectra (lambda(max) = 642 nm), and good solubility in organic solvents compared to the frequently used tris(bipyridine) Ru(II) complexes. The electrochemical measurements for these Ru complexes showed reversible and quasi-reversible redox processes, implying a potential improvement in the stability of the electroluminescent device. The electrophosphorescent devices were fabricated by doping them in a polymer host using a simple solution spin-coating technique. For a single-layer device with the 1.0 wt % Ru(dbeb)(2+)-doped polymer blends of poly(vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD) as the emitting layer and with the metal Ba as the cathode, an external quantum efficiency of 3.0%, a luminous efficiency of 2.4 cd/A, and a maximum brightness of 935 cd/m(2) are reached with an electroluminescence (EL) spectral peak at 640 nm and Commission Internationale de L'Eclairage chromaticity coordinates of x = 0.64 and y = 0.33, which were comparable with standard red color.
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