Search

ABSTRACT Blue light-emitting polyfluorenes, PPF-FSOs and PPF-SOFs were synthesized via introducing spiro[fluorene-9,9′-thioxanthene- S,S-dioxide] isomers (2,7-diyl and 2′,7′-diyl) (FSO/SOF) into the poly[9,9-bis(4-(2-ethylhexyloxy) phenyl)fluorene-2,7-diyl] (PPF) backbone, respectively. With the increasing contents of FSO and SOF moieties, the absorption and PL spectra of PPF-FSOs show slight red shift, while that of PPF-SOFs exhibit blue shift, respectively. The HOMO and LUMO levels reduce gradually with increasing SOF unit in PPF-SOFs. The polymers emit blue light peaked around 430-445 nm and show an excellent spectral stability with the variation in current densities. The distinctly narrowing EL spectra were observed with the incorporation of isomers in the polymers. The full width at half maximum reduced by 15 nm for PPF-SOFs, resulting in a blue shift with the CIE coordinates from (0.16, 0.11) to (0.16, 0.08). With a device configuration of ITO/PEDOT:PSS/EML/CsF/Al, a maximum luminance efficiency (LEmax) of 2.00 cd A−1, a maximum external quantum efficiency (EQEmax) of 3.76% with the CIE coordinates of (0.16, 0.08) for PPF-SOF15 and a LEmax of 1.68 cd A−1, a EQEmax of 2.38% with CIE (0.16, 0.12) for PPF-FSO10 were obtained, respectively. The result reveals that spiro[fluorene-9,9′-thioxanthene- S,S-dioxide] isomers are promising blocks for deep-blue light-emitting polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2332-2341 [ABSTRACT FROM AUTHOR]

ABSTRACT Six new conjugated polymers comprising of carbazole, fluorene, and ethylene dioxythiophene (EDOT) moieties along the backbone with a pendant cyano group attached to the ethylene moiety have been designed and synthesized via Sonogashira coupling polymerization reaction. Optical and electrochemical characterizations have shown that the energy band gaps lie within the range of 2.35-2.44 eV. Additionally, the presence of carbazole and EDOT makes these polymers better hole transporting materials, which is reflected from their low oxidation potential peaks (0.55-1.11 V) in cyclic voltammograms. Furthermore, the aggregation enhanced emission (AEE) phenomenon resulted in a 2.6-fold increase in fluorescence intensity in a 90:10 THF/water mixture in comparison to pristine THF. The AEE properties were further verified by DLS (dynamic light scattering) experiment and SEM (scanning electron microscopy) studies. Polymers in solution as well as in polystyrene matrix emit in the green region (quantum yield in solution state Φ f =41-43%) with CIE values (0.25-0.36, 0.52-0.57). Excellent thermal stability is observed for the new polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2774-2784 [ABSTRACT FROM AUTHOR]

ABSTRACT Two D-π-A-type 2,2,2-trifluoroacetophenone derivatives, namely, 4′-(4-( N, N-diphenyl)amino-phenyl)-phenyl-2,2,2-trifluoroacetophenone (PI-Ben) and 4′-(4-(7-( N, N-diphenylamino)-9,9-dimethyl- 9H-fluoren-2-yl)-phenyl-2,2,2-trifluoroacetophenone (PI-Flu), are developed as high-performance photoinitiators combined with an amine or an iodonium salt for both the free-radical polymerization of acrylates and the cationic polymerization of epoxides and vinyl ether upon exposure to near-UV and visible light-emitting diodes (LEDs; e.g., 365, 385, 405, and 450 nm). The photochemical mechanisms are investigated by UV-Vis spectra, molecular-orbital calculations, fluorescence, cyclic voltammetry, photolysis, and electron-spin-resonance spin-trapping techniques. Compared with 2,2,2-trifluoroacetophenone, both photoinitiators exhibit larger redshift of the absorption spectra and higher molar-extinction coefficients. PI-Ben and PI-Flu themselves can produce free radicals to initiate the polymerization of acrylate without any added hydrogen donor. These novel D-π-A type trifluoroacetophenone-based photoinitiating systems exhibit good efficiencies (acrylate conversion = 48%-66%; epoxide conversion = 85%-95%; LEDs at 365-450 nm exposure) even in low-concentration initiators (0.5%, w/w) and very low curing light intensities (1-2 mW cm−2). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1945-1954 [ABSTRACT FROM AUTHOR]

We have developed a metal-free process for the aerobic photooxygenation of sulfides to sulfoxides mediated by riboflavin tetraacetate or riboflavin (vitamin B2) photocatalysts and visible light (450 nm) in an acetonitrile-water (85:15 v/v) mixture. The optimised solvent system leads to both singlet-oxygen and electron-transfer pathways in photooxygenation, thus allowing oxidation of electron-poor and electron-rich thioanisoles, dialkyl sulfides and sterically hindered sulfides. Besides having a broad substrate scope, the method has very short reaction times and requires low catalyst loading (down to 0.1 mol%). These properties are due to the high photocatalyst stability and the extremely high quantum yields (1.3 for thioanisole oxygenation). Moreover, the method is chemoselective, producing only sulfoxides without overoxidation to sulfones. Taking into account the broad substrate scope, high selectivity and high efficiency, this method distinguishes itself from those previously reported. Other advantages include easy work-up of the reaction mixture, the availability and biodegradability of the photocatalysts and mild reaction conditions. We demonstrated, on a preparative scale, its practical application in the synthesis of the psychostimulant modafinil, in the selective oxidation of methionine derivatives, and in the detoxification of mustard gas. [ABSTRACT FROM AUTHOR]

ABSTRACT Carrier balance is essential to obtain efficient emission in polymer light-emitting diodes (PLEDs). A new polymer 3P5O composed of alternating p-terphenyl and tetraethylene glycol ether segments is designed and synthesized by the Suzuki coupling reaction and successfully employed as hole-buffer layer to improve carrier balance. Multilayer PLEDs [ITO/PEDOT:PSS/ 3P5O/SY/LiF/Al], with Super Yellow (SY) as the emitting layer and 3P5O as the hole-buffer layer, reveal maximum luminance (17,050 cd/m2) and maximum current efficiency (6.6 cd/A) superior to that without the hole-buffer layer (10,017 cd/m2, 3.0 cd/A). Moreover, it also shows better performance than that using conventional BCP as hole-blocking layer [ITO/PEDOT:PSS/SY/BCP/LiF/Al (80 nm): 13,639 cd/m2, 4.1 cd/A]. The performance enhancement has been attributed to hole-buffering characteristics of 3P5O that results in improved carrier recombination ratio and wider carrier recombination region. Current results indicate that the 3P5O is a promising hole-buffer polymer to enhance the performance of optoelectronic devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 785-794 [ABSTRACT FROM AUTHOR]

ABSTRACT Two pyrene-functionalized oligofluorenes (TPA-PyF3 and CBP-PyF3) are prepared using the condensation reaction by the Friedel-Crafts procedure. In the produced oligomers, the triphenylamine or N, N′-dicarbazolyl-4,4′-biphenyl core serves as a spacer bearing spiro-linked fluorene moieties to form a multi-H shaped structure. This specific structure efficiently retards the crystallization tendency of the pyrene groups, and gives the materials completely amorphous morphological structure and film forming ability. Solution-processed OLEDs with the structure of ITO/PEDOT:PSS (25 nm)/TPA-PyF3 or CBP-PyF3 (40 nm)/TPBI (35 nm)/Ca (10 nm)/Ag (100 nm) show low turn-on voltages of 3.6 V, and the maximum external quantum efficiencies reach 1.78% and 2.07% for TPA-PyF3 and CBP-PyF3, respectively. Moreover, both devices exhibit stable deep-blue light emission with Commission International de I'Eclairage (CIE) coordinates of around (0.16, 0.09) at the brightness of 100-1000 cd m−2. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 795-801 [ABSTRACT FROM AUTHOR]

ABSTRACT N, N'-dibutylquinacridone (DBQA) is utilized here for the first time as a high-performance panchromatic photoinitiator for the cationic polymerization (CP) of epoxides, the free radical polymerization (FRP) of acrylates, the thiol-ene polymerization and the synthesis of interpenetrated polymer networks (epoxide/acrylate) under violet, blue, green and yellow lights (emitted from LED at 405 nm, 470 nm, 520 nm, or 594 nm, or laser diode at 532 nm). It confers a panchromatic character to the photopolymerizable matrices. Remarkably, the proposed DBQA based photoinitiating systems exhibit quite excellent efficiency (the final monomer conversion for multifunctional monomers at room temperature can reach 62% and 50% in CP and FRP, respectively) and appear as much more powerful than the camphorquinone or Eosin-Y containing reference systems for visible light. For green light, DBQA is much more reactive than the literature reference (Eosin-Y) and for blue light, a good reactivity is found compared with camphorquinone. The photochemical mechanisms are studied by molecular orbital calculations, steady state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis, and electron spin resonance spin trapping techniques. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1719-1727 [ABSTRACT FROM AUTHOR]

ABSTRACT Two new thermally crosslinkable hole-transporting polymers, X-PTPA and X-PCz, were synthesized via Yamamoto coupling reactions. The number-averaged molecular weights ( Mn) of X-PTPA and X-PCz were found to be 45,000 and 48,000, respectively, and therewith, polydispersity indices were of 1.8 and 1.7, respectively. Thermally crosslinked X-PTPA and X-PCz exhibit excellent solvent resistance and stable optoelectronic properties. The UV-visible maximum absorption peaks of X-PTPA and X-PCz in the thin film state are at 389 and 322 nm, respectively. The HOMO levels of X-PTPA and X-PCz are estimated to be −5.27 and −5.39 eV, respectively. Multilayered devices (ITO/crosslinked X-PTPA or X-PCz/SY-PPV/LiF/Al) were fabricated with SY (SuperYellow) as the emitting layer. The maximum efficiency of the multilayered device with a crosslinked X-PTPA layer is approximately three times higher than that of the device without a crosslinked X-PTPA layer and much higher than that of the crosslinked X-PCz device. This result can be explained by the observations that crosslinked X-PTPA produces increased electron accumulation within the emitter, SY, and also efficient exciton formation due to improved charge balance. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5111-5117 [ABSTRACT FROM AUTHOR]

Polyfluorene PF•γCD rotaxane copolymer, composed of randomly distributed 9,9-dioctylfluorene, methyltriphenylamine (electron-donating) and 9-dicyanomethylenefluorene complexed with γ-cyclodextrin (γCD) (electron-accepting) structural units, has been synthesized by Suzuki cross-coupling reaction. The chemical structures were proved by FTIR and 1H NMR spectroscopy. The surface morphology, thermal, optical, electrochemical behavior, and adhesion characteristics of the obtained rotaxane copolymer have been investigated and compared with those of the nonrotaxane counterpart ( PF). Relatively high fluorescence efficiency, almost identical normalized absorbance maximum in solution and solid-state of PF•γCD rotaxane copolymer, and a more uniform and smoother surface with lower adhesion forces provides the role of γCD encapsulation on the lower aggregation propensity. PF•γCD and PF copolymers exhibit n- and p-doping processes and blue-light emission in the film state. The optical and electrochemical band gaps (Δ Eg), as well as the highest occupied molecular orbital/lowest unoccupied molecular orbital positions in an energetic diagram indicate that both copolymers are promising blue-emitting electroluminescent materials. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 [ABSTRACT FROM AUTHOR]