Poly(9,9-dialkyl-3,6-dibenzosilole)--a high energy gap host for phosphorescent light emitting devices

The preparation of the 3,6-disubstituted dibenzosilole monomers , and by two different routes is described; Suzuki copolymerisation afforded poly(9,9-dioctyl-3,6-dibenzosilole) which has a sufficiently high triplet energy (2.55 eV) to function as a host for green electrophosphorescent emitters.     

Synthesis,characterization, and electrogenerated chemiluminescence of deep blue emitting eumelanin‐inspired poly(indoylenearylene)s for polymer light emitting diodes

Deep blue emitting copolymers were synthesized by uniting the Eumelanin‐inspired indole core with fluorene and carbazole units via Suzuki polymerization. The resulting polymers, PIF and PIC, showed deep blue emission in the range of 416–418 nm and quantum yields of 0.39–0.60. Both polymers exhibited an intense and stable electrogenerated chemiluminescence. Interestingly, deep HOMO levels of −5.71 and −5.61 eV were observed for PIF and PIC, respectively. Solution processed polymer light emitting diodes (PLEDs) were fabricated using the PIF as a guest. PLEDs emitted deep blue light at 418 nm, with the luminous efficiency peaking at 1 Cd/A, given that the photopic response at that wavelength is 0.0151. The electroluminescence of PIF displayed a Commission Internationale de l'Eclairage coordinates of (0.16, 0.07) with a maximum external quantum efficiency of 1.1%. Hence, these materials prove to be promising candidates for the fabrication of deep blue PLEDs. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 125–131     

Synthesis and characterization of a soluble blue light emitting alternating copolymer

An alternating copolymer with monomer units of fluorene and phenylenedivinylene was synthesized by reaction between n-hexyl fluorene phosphonium salt and isophthalic aldehyde based on the Wittig reaction. The polymer solution in chloroform was made into a film with a very fine surface by spin-casting on indium-tin oxide (ITO) coated glass to fabricate a light emitting diode (LED) with an aluminum negative electrode. The optical absorption spectrum of the solid film shows a peak at 370 ran while the PL spectrum has the main peak at 560 nm with a secondary peak at 440 nm and the EL spectrum has a single peak at 560 nm showing the Stokes shift of 190 nm. The peak in the PL spectrum shifts to 420 nm with a vibronic structure at 440 nm on either dilution by chloroform or blending with polyvinylcarbazole (PVK). The emissive polymer bulk seemed to generate sites for excimers and molecular aggregates which were diminished on the dilution or blending. The peak in the EL spectrum also shifts to 440 nm on blending of 20% of the copolymer with PVK. Further dilution to 10% of the copolymer shifts the EL peak to 420 nm with the onset potential of 15 V and the highest quantum efficiency of 0.01% in this series. The concentrated channels were developed in the blends with severe phase separation to show a lower onset potential but poor quantum efficiency.     

Synthesis of extremely stable blue light emitting poly(spirobifluorene)s with Suzuki polycondensation

[reaction: see text] Full spirobifluorene-based blue light emitting polymers, which exhibited extraordinary thermal and color stability, were prepared with SPC through an AB-type monomer route.     

Electronic properties of anthracene derivatives for blue light emitting electroluminescent layers in organic light emitting diodes: a density functional theory study

Molecular level parameters are investigated computationally to understand the factors that are responsible for the higher efficiency in derivatives of 9,10-bis(1-naphthyl)anthracene (alpha-ADN), 9,10-bis(2-naphthyl)anthracene (beta-ADN), their tetramethyl derivatives (alpha,beta-TMADN) and the t-Bu derivative (beta-TBADN) as blue light emitting electroluminescent (EL) layers in organic light emitting diodes (OLEDs). DFT studies at the B3LYP/6-31G(d,p) level have been carried out on the substituted anthracenes. The absorption spectra are simulated using time dependent DFT methods (TD-DFT) whereas the emission spectra are approximated by optimizing the excited state by HF/CI-Singles and then carrying out the vertical CI calculations by the TD-DFT method. The reorganization energy for estimating the hole and electron transport is calculated. The transfer integrals between parallely stacked molecules in the bulk state are estimated by calculating the electronic splitting. The substituted anthracenes are compared with unsubstituted anthracene and yet untested 9,10-dianthrylanthracene (TANTH). A larger and slower buildup of the electrons and holes in the EL layer, due to the higher reorganization energy and smaller electronic coupling between the adjacent molecules could lead to an increase in hole-electron recombination in the layer and thus increase the efficiency.     

A pure blue light emitting binaphthyl derivative：Synthesis and properties

A binaphthyl derivative with pyrene on 3 and 3＇ positions was synthesized and characterized via Suzuki coupling reaction. Emission maximum in solution was located at 390 nm with a quantum efficiency of 68% by taking 9,10-diphenyl anthracene as reference,while it is shifted to 450 nm with FWHM of 104 nm resulting from aggregation state in solid film.Glass transition temperature（Tg）and decomposition temperature were measured to be 184 and 447℃,respectively,by DSC and TGA.Unlike its photoluminescence spectrum,electroluminescent spectrum peaked at about 460 nm and shows a FWHM of 69 nm corresponding to a pure blue emission.The turn-on voltage,luminance and efficiency maximum were 5 V,2953 cd/m^2 and 1.37cd/A with CIE color coordinate of（0.16,0.15）,in the device structure of ITO/NPB（40nm）/PY-BN-PY（15nm）/BPhen（40nm）/Mg：Ag.     

High-efficiency pyrene-based blue light emitting diodes: aggregation suppression using a calixarene 3D-scaffold

An efficient blue light emitting diode based on solution processable pyrene-1,3-alt-calix[4]arene is demonstrated, providing a record current efficiency of 10.5 cd A(-1) in a simple non-doped OLED configuration. Complete suppression of pyrene aggregation in the solid state is achieved by controlling chromophore dispersion using the 1,3-alt-calix[4]arene scaffold.     

Excimer suppression mechanism in light emitting polymer blends

Alternating copolymer of distyrylenediethylhexyloxyphenylene and phenyltriazine(PPVT) or hydroxyphenyltriazine(PVOT) is synthesized in order to enhance the electron mobility in the light emitting polymers. Photoluminescence(PL) spectrum of PPVT shows excimeric characteristics but PVOT generates excitonic PL emission. A blend of PVOT with polyvinylcarbazole(PVK) enhances the PL intensity of PVOT on photoexcitation of PVK indicating an efficient energy transfer. The excimeric PL emission of PPVT is suppressed on photoexcitation of a blend with PVK at the UV-visible absorption(AB) maximum of PVK, which is an indirect photoexcitation, while the energy transfer from PVK to PPVT is not completed.     

Steric inhibition of pi-stacking: 1,3,6,8-tetraarylpyrenes as efficient blue emitters in organic light emitting diodes (OLEDs)

The sterically congested tetraarylpyrenes 1-3, which can be readily accessed by Suzuki coupling, exhibit no-aggregation (pi-stacking) behavior in both solution and solid states. The indisposed tendency of 1-3 toward crystallization and their moderate molecular dimensions permit exploitation as blue light emitting materials in OLEDs with respectable device performances.     

Soluble blue light emitting pyridine-containing polymers prepared by oxidative-coupling copolymerization

Novel polymers containing pyridine moieties in main chains have been prepared by facile oxidative-coupling co-polymerization of pyridine N-oxide with N-alkyl carbazole and fluorene as the precursor polymers, which were reduced to the pyridine-containing polymers respectively. The polymers were characterized by FT-IR, ¹H NMR, UV-Vis, X-ray, thermo-gravimetric analysis, and fluorescence spectroscopy. The pyridine-containing polymers good solubility in convenient organic solvents, high thermal stability with the onset decomposition temperature above 310 °C. The electrochemical behaviors of the polymers were investigated by cyclic voltammetry; the HOMO and LUMO energy level of the polymers were estimated from the electrochemistry and UV-Vis spectroscopy. The fluorescence spectra of the pyridine-containing polymers display blue light emitting properties in both solution and solid-state film.     

A new temperature-sensitive polymer: Poly(ethoxypropylacrylamide)

In this study, a new temperature sensitive polymer was obtained by the solution polymerization of ethoxypropylacrylamide. The monomer, N-(3-ethoxypropyl)-acrylamide was synthesized by the nucleophilic substitution reaction of 3-ethoxy-propylamine and acryloyl chloride. The solution polymerization was performed in ethanol at 70 °C, by using azobisizobutyronitrile as the initiator. Poly(N-(3-ethoxypropyl)acrylamide), PEPA, exhibited a reversible phase transition by the temperature. The effects of polymer and salt concentrations on the lower critical solution temperature, (LCST) behaviour were investigated. LCST was found to be strongly dependent on the polymer concentration. The dynamic light scattering (DLS) measurements confirmed the formation of aggregates by the association of nucleated polymer chains at the temperatures higher than LCST. However an unusual behaviour, a marked decrease in the hydrodynamic diameter by the increasing PEPA concentration was observed below the LCST. The effect of salt concentration on the critical flocculation temperature of PEPA was reasonably similar to poly(isopropylacrylamide), PNIPA. In the ethanol-water media, the reversible phase transition behaviour was observed up the ethanol concentration of 30% v/v. This study indicated that PEPA was a new alternative thermally reversible material for PNIPA. With respect to the well-defined temperature-sensitive polymers like PNIPA, polymer concentration dependent LCST of PEPA can provide significant advantages in the applications like drug targeting, affinity separation and immobilization of bioactive agents.     

Poly(styrene-acrylic acid) magnetic polymer microspheres

Magnetic polymer microspheres have been considered as a kind of new biopolymer materials with great advantages in bioseparation engineering and biomedicine engineering because they have not only polymer functional groups but also magnetic characteristics. Styrene-acrylic acid copolymer (p(S-AA)) magnetic microspheres were synthesized by dispersion polymerization with Fe₃O₄ as core and p(S-AA) as shell. The microspheres were characterized by SEM, size analysis, molecular weight and solid content measurement. All of them indicate that the microspheres are small in size, narrow in distribution, stable in chemistry and rich in functional groups on their surface. __________ Translated from Journal of Beijing Union University (Natural Science) 2008, 21(3): 82–84     

Poly(carbon suboxide): A photosensitive paramagnetic ladder polymer

Carbon suboxide was found to give, on photo- and thermal-polymerization, a photosensitive paramagnetic polymer. Studies of the kinetics of the ESR signal growth accompanying the polymerization process complement documented results obtained from monitoring the rate of polymer production and monomer disappearance. The spin concentration of the polymer increases with higher reaction temperature, reaching 2 × 10¹⁹ spin/g at a polymerization temperature of 105°C. The paramagnetism of poly(carbon suboxide) follows the Curie—Weiss law. Relaxation behavior at room temperature and g values for the spin systems have been obtained. The 105°C polymer shows a Weiss constant equal to 17°K and an extremely narrow ESR line width, ca. 10 mG, at 5°K. The ¹³C coupling constant from the selectively labeled polymer indicates π-electron delocalization over the ladder polymer. The polymer paramagnetism can be further reversibly enhanced by visible light irradiation. The steady-state concentration of the photo-ESR signal is proportional to the square root of incident light intensity, with a quantum yield at room temperature for charge accumulation equal to 5% at an incident light level of 10¹⁵ photons/sec-cm². Fluorescence and excitation spectra of the soluble fraction of poly(carbon suboxide) are presented together with the quantum yield. The polymer has also been found to be an effective photopolymerization initiator at wavelengths longer than 340 nm.     

Poly(P-phenylene sulfide) hexafluoroarsenate: A novel conducting polymer

Poly(p-phenylene sulfide) (PPS) is a melt- and solution-processible polymer which on treatment with AsF₅ forms a blue-black material with a conductivity of 1–10 Ω^?1 cm^?1. Thermopower measurements indicate that the resulting polymer is p type, consistent with partial oxidation of the PPS by the AsF₅. The rate and extent of this doping process prove to be particularly sensitive to the degree of crystallinity of the starting polymer. There is also evidence of crosslinking of the polymer chains during the reaction with AsF₅. The details of both the chemistry and physics of the doping of PPS and several of its derivatives are presented.     

Degradation effects in polymer light emitting devices due to heat treatment

The characteristics of polymer light emitting diodes (PLEDs) (ITO/PPV/Ca) depend strongly on the conditions during preparation and operation. We studied the effects of heat treatment (during and after preparation) of PLEDs with OC₁C₁₀-PPV as active layer. PLEDs showed a reduction of both the current and the light output to 40 % after annealing for only 30 min at 65 °C. Effects on I-V characteristics were studied by measuring single carrier devices (hole- and electron-dominated devices). The current reduction after heat treatment can be ascribed to degradation of the ITO/PPV and the Ca/PPV interfaces.     

Synthesis of regio- and stereoselective alkoxy-substituted spirobifluorene derivatives for blue light emitting materials

Three new octyloxy substituted spirobifluorenes, 2,7-diphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DPBSBF, 1a), 2,7-dibiphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DBBSBF, 1b) and 2,7-diterphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DTBSBF, 1c) were prepared. All the compounds had been fully characterized by ¹H and ¹³C NMR, UV-Vis, DSC, mass spectrometry and gave satisfactory elemental analyses. They possessed good solubility in common organic solvents and good homogeneous film formation. The optical energy band gap of DBBSBF was 3.27 eV between the HOMO energy level, 5.85 eV, measured by UPS and the LUMO, 2.58 eV, calculated from absorption spectrum. A blue organic light emitting diode (OLED) based on the structure of ITO/TPD (60 nm)/DBBSBF (40 nm)/Alq₃ (20 nm)/LiF (1 nm)/Al (100 nm) showed good performance. The luminance of 3125 cd/m² was observed at a drive voltage of 12.8 V and the colour coordinate in CIE chromaticity was (0.14, 0.12). The external quantum efficiency was obtained to be 2.8% at 100 cd/m².     

New benzo[b]furans as electroluminescent materials for emitting blue light

[structure: see text] New functionalized mono- and bis-benzo[b]furan derivatives were synthesized and developed as blue-light emitting materials. They possessed a CN, CHO, CH=CHPh, CH=CPh(2), or CH=CHCOOH group at the C4-position. Two benzo[b]furan nuclei in bis-benzo[b]furan derivatives were connected by a divinylbenzene bridge. With good volatility and thermal stability, bis-benzo[b]furan 7a was fabricated as a device. It emitted blue light with brightness 53430 cd/m(2) (at 15.5 V) and high maximum external quantum efficiency 3.75% (at 11 V).