Fluorene-substituted pyrenes—Novel pyrene derivatives as emitters in nondoped blue OLEDs (original) (raw)
Related papers
Pyrene-Benzimidazole Derivatives as Novel Blue Emitters for OLEDs
Molecules
Three novel small organic heterocyclic compounds: 2-(1,2-diphenyl)-1H-benzimidazole-7-tert-butylpyrene (compound A), 1,3-di(1,2-diphenyl)-1H-benzimidazole-7-tert-butylpyrene (compound B), and 1,3,6,8-tetra(1,2-diphenyl)-1H-benzimidazolepyrene (compound C) were synthesized and characterized for possible applications as blue OLED emitters. The specific molecular design targeted decreasing intermolecular aggregation and disrupting crystallinity in the solid-state, in order to reduce dye aggregation, and thus obtain efficient pure blue photo- and electroluminescence. Accordingly, the new compounds displayed reasonably high spectral purity in both solution- and solid-states with average CIE coordinates of (0.160 ± 0.005, 0.029 ± 0.009) in solution and (0.152 ± 0.007, 0.126 ± 0.005) in solid-state. These compounds showed a systematic decrease in degree of crystallinity and intermolecular aggregation due to increasing steric hindrance, as revealed using powder X-ray diffraction analysis an...
Pyrenylpyridines: Sky-Blue Emitters for Organic Light-Emitting Diodes
ACS Omega
A novel sky-blue-emitting tripyrenylpyridine derivative, 2,4,6-tri(1-pyrenyl)pyridine (2,4,6-TPP), has been synthesized using a Suzuki coupling reaction and compared with three previously reported isomeric dipyrenylpyridine (DPP) analogues (2,4-di(1pyrenyl)pyridine (2,4-DPP), 2,6-di(1-pyrenyl)pyridine (2,6-DPP), and 3,5-di(1-pyrenyl)pyridine (3,5-DPP)). As revealed by single-crystal X-ray analysis and computational simulations, all compounds possess highly twisted conformations in the solid state with interpyrene torsional angles of 42.3°−57.2°. These solid-state conformations and packing variations of pyrenylpyridines could be correlated to observed variations in physical characteristics such as photo/thermal stability and spectral properties, but showed only marginal influence on electrochemical properties. The novel derivative, 2,4,6-TPP, exhibited the lowest degree of crystallinity as revealed by powder X-ray diffraction analysis and formed amorphous thin films as verified using grazing-incidence wide-angle X-ray scattering. This compound also showed high thermal/photo stability relative to its disubstituted analogues (DPPs). Thus, a nondoped organic light-emitting diode (OLED) prototype was fabricated using 2,4,6-TPP as the emissive layer, which displayed a sky-blue electroluminescence with Commission Internationale de L'Eclairage (CIE) coordinates of (0.18, 0.34). This OLED prototype achieved a maximum external quantum efficiency of 6.0 ± 1.2% at 5 V. The relatively high efficiency for this simple-architecture device reflects a good balance of electron and hole transporting ability of 2,4,6-TPP along with efficient exciton formation in this material and indicates its promise as an emitting material for design of blue OLED devices.
Chemistry - A European Journal, 2011
We present here a cruciform oligo(phenylenevinlyene) 2,5,2′,5′-tetrastyrylbiphenyl (TSB) exhibits excellent properties as host material for blue emitting guest molecule 1,4-di(4′-N,N-diphenylaminostyryl)benzene (DPA-DSB). TSB, which is constructed by linking two rigid distyrylbenzene (DSB) through the phenyl-phenyl bond, shows good optical and electronic properties e.g. high photoluminescent (PL) efficiency and wide band gap similar to DSB. Meanwhile, the central biphenyl core in TSB, which allows the relatively free rotation of two DSB segments along the biphenyl bond, makes it to be conformational multiformity and relatively flexible. As the result, TSB shows the good film forming property and larger loading ability to the guest molecules. The PL efficiencies of guest-host films of DPA-DSB and TSB arrive at the high level around 70% (68% for the 2 wt % DPA-DSB doped film and 72% for the 8 wt % DPA-DSB doped film), which is approaching the PL efficiency of the guest DPA-DSB in dilute solution (78%), indicating that the host TSB can sufficiently disperse the guest DPA-DSB with little aggregation. The organic light-emitting devices using DPA-DSB (2 wt %) doped TSB as blue emitting layer show the maximum efficiency of 12.2 cd/A (6.2%) and 6.39 lm/W, and the maximum brightness of 17350 cd/m 2 . Upon further analysis, it has been revealed that the Förster energy transfer and charge trapping are demonstrated to cooperatively work in this doping system.
Fluorescent pyrene-imidazole material for deep-blue organic light-emitting devices
Numerous endeavors have been exerted to devise deep-blue light-emitting materials (LEMs) for organic lightemitting devices (OLEDs). Nevertheless, deep-blue light-emitting materials exhibiting high efficiency for simple-structured OLEDs are still scarce. Herein, a donor-acceptor based LEM, 4'-(4, 5-diphenyl-1-(3-(pyren-1-yl) phenyl)-1H-imidazole-2-yl)-N,N-diphenylbiphenyl-4-amine (TPA-PyI) is developed by merging imidazole, triphenyl-amine and pyrene units for OLEDs. TPA-PyI is used as the emitting layer in OLED device, which emits a deep-blue fluorescence at 444 nm. With a current efficiency (CE) of 3.05 cd/A and a power efficiency (PE) of 2.95 lm/W, an EQE of 2.97% is achieved. High thermal-stability is achieved with decomposition-temperature (T d) of 516 • C.
Australian Journal of Chemistry, 2012
The synthesis and characterisation of 2,5-bis(5′-hexyl-[2,2′-bithiophen]-5-yl)pyridine (Th4PY) and its use as a blue emitter in organic light emitting diodes (OLEDs) is reported. Th4PY was synthesised in high yield using a straightforward Suzuki coupling route with commercially available starting materials. As Th4PY is both soluble and has low molecular weight, blue OLEDs were fabricated using both spin-coating and vacuum deposition thin film processing techniques to study the effect of processing on device performance. OLED devices using a spin-coated layer consisting of 4′,4′′-tris(N-carbazolyl)triphenylamine (TCTA) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a host matrix together with Th4PY as emitter exhibited highly efficient sky-blue emission with a low turn-on voltage of 3 V, a maximum brightness close to 15000 cd m–2 at 8 V, and a maximum luminous efficiency of 7.4 cd A–1 (6.3 lm W–1) with CIE coordinates of x = 0.212, y = 0.320. The device perform...
Journal of Materials Chemistry, 2009
We found an unusual way in improving electroluminescence efficiency of blue organic light-emitting diodes (OLEDs). Two electron deficient 4,5-diazafluorene-or di(2,2 0 -pyridyl)-containing blue fluorophores, PhSP N2 DPV (4,5-diaza-2 0 -diphenylamino-7 0 -(2,2 00 -diphenylvinyl)-9,9 0 -spirobifluorene) and PhF py2 DPV (N-[7-(2,2-diphenylvinyl)-9,9 0 -di(2,2 00 -pyridyl)-2-fluorenyl]-N,N-diphenylamine), were synthesized and characterized for non-doped blue OLEDs. Whereas PhF py2 DPV OLED performs ordinarily, PhSP N2 DPV OLED outperforms previously known PhSPDPV (2-diphenylamino-7diphenylvinyl-9,9 0 -spirobifluorene) OLED significantly: maximum external quantum efficiency of $5% (4.6% at 20 mA cm À2 ) and the peak electroluminance of 60510 cd m À2 (1810 cd m À2 at 20 mA cm À2 ) versus 3.4% (2.9% at 20 mA cm À2 ) and 33020 cd m À2 (910 cd m À2 at 20 mA cm À2 ) of PhSPDPV OLED. We attribute the superior performance of PhSP N2 DPV OLED to the good charge balancing, which is in turn due to the very low hole mobility of PhSP N2 DPV. The experimental results reveal that the electron-deficient moiety, 4,5-diazafluorene or di(2,2 0 -dipyridyl), increases electron affinity but reduces the hole mobility. Electron mobility, determined by time-of-flight (TOF) method, is 5 Â 10 À5 and 5 Â 10 À4 cm 2 V À1 s À1 (at an electric field of 4.9 Â 10 5 V cm À1 ) for PhSP N2 DPV and PhF py2 DPV, respectively. Surprisingly, they are not higher than 8 Â 10 À4 cm 2 V À1 s À1 of nonpolar PhSPDPV. On the other hand, hole mobility is 2 Â 10 À6 and 2 Â 10 À4 cm 2 V À1 s À1 for PhSP N2 DPV and PhF py2 DPV, respectively, and they are both significantly lower than 6 Â 10 À3 cm 2 V À1 s À1 of PhSPDPV. For PhSP N2 DPV and PhF py2 DPV bipolar blue fluorophores, we have demonstrated that electron-transporting and lightemitting functions involve different molecular halves. The design of such molecular halves greatly facilitates the optical and electronic optimizations of fluorophores for high-performance OLEDs.
Dyes and Pigments, 2017
A rational design strategy is proposed for synthesis of a new deep-blue emitter/dopant (denoted as TPA-3FA) based on triphenylamine (TPA) as the core with the addition of diethylfluorene/acridine analogues to frame a star-shaped material for solution processable high performance OLEDs. The photophysical, thermal, electrochemical, electronic, and hole transporting properties of TPA-3FA are examined. Most importantly, this rational design strategy of introducing diethylfluorene between TPA and acridine imparts high rigidity and non-planarity, which in turn completely suppress intermolecular interactions, and thus yields a strong narrow deep-blue fluorescence with a high quantum yield. Moreover, a solution processed non-doped device with TPA-3FA as an emitter exhibits excellent device performance with a maximum external quantum efficiency (EQE) of 4.43%, CIE (x,y) coordinates of (0.153, 0.045) and good device stability. The device performance was significantly improved with an EQE of 6.11% and CIE (x,y) coordinates of (0.156, 0.049) after doping into a host. The same device when processed in a halogen-free solvent exhibited an impressive EL performance (EQE: 5.72%; CIE (0.157, 0.046)).
2008
Solution processable blue fluorescent dendrimers based on cyclic phosphazene (CP) cores incorporating amino-pyrene moieties have been prepared and used as emissive layers in organic light emitting diodes (OLEDs). These dendrimers have high glass transition temperatures, are monodisperse, have high purity via common chromatographic techniques, and form defect-free amorphous films via spin/dip coating. The solution processable blue light emitting OLEDs reach current efficiencies of 3.9 cd/A at brightness levels near 1000 cd/m 2. Depending on the molecular bridge used to attach the fluorescent dendron to the inorganic core, the emission wavelength changes from 470 to 545 nm, corresponding to blue and green light respectively. Via dilution experiments we show that this shift in emission wavelength is likely associated with molecular stacking of the amino-pyrene units.