Differently substituted benzothiadiazoles as charge-transporting emitters for fluorescent organic light-emitting diodes (original) (raw)
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Dyes and Pigments, 2019
New efficient carbazole-based emitters containing tetra-/triphenylethene units were developed for boosting efficiency of non-doped fluorescent organic light-emitting diodes. Comparable study of the properties of derivatives containing one or two tetra-/triphenylethenyl units was performed using various experimental and theoretical techniques. Depending on the substitution pattern, emitters exhibited strong blue or green emission, which was enhanced by aggregation. Compounds with two substituents showed higher glass transition temperatures (up to 120 ºC) and lower ionization potentials (of ca. 5.15 eV) comparing to mono substituted derivatives. Time-of-flight hole drift mobility values of the studied compounds with two substituents reached 10-3 cm 2 /Vs at high electric fields. Non-doped fluorescent OLEDs based on carbazole derivative containing two tetraphenylethenyl units demonstrated extremely high external quantum efficiency as for simple fluorescent organic light-emitting devices, which reached 5.32 %.
The role of carbazole in organic light-emitting devices
Synthetic Metals, 1996
New organic oligomers and polymers based on the carbazole molecule are explored for possible applications in light-emitting devices. In one case, (butyl-or octyl-) carbazole dimers and poly(N-butyl-3,6-carbazolylene) polymer were used as the hole-transporting and lightemitting layer in multilayer light-emitting diodes (LEDs). These devices yielded bright blue light (as much as about 6000 cd m-2) with high external quantum (about 10%) and luminance efficiencies (about 21m W-1). The other case involved ([3-octylthiophene J-[bis-(Nethyl or octyl carbazolylene) ]) multiblock copolymers as the active emitting layer in single-layer LEDs. Color tuning was achieved in these devices by changing the number of monomer units contained in the thiophene chain. We also observed an increase of the external quantum efficiency in diodes based on the copolymers with short thiophene segments that we attributed to a more balanced charge injection.
A series of novel carbazole-based materials, DPACz1, DPACz2 and DPACz3 having diphenylamino moieties at 1-and 8-positions of carbazole have been synthesized and characterized for the first time. The introduction of diphenylamino substituents at 1-or 1,8-positions of carbazole resulted into increase of the band-gap compared with the previously reported 3,6-or 2,7-substituted ones. The HOMO levels increased from DPACz1 to DPACz2 with the addition of one additional diphenylamino unit, and further increased in case of DPACz3, a dimer of DPACz1 having a benzidine moiety. The materials have high triplet energy levels of 2.68, 2.60 and 2.45 eV, respectively. Based on suitable HOMO levels and high triplet energies, the newly synthesized diphenylaminocabazoles were investigated for their potential as solution-processable host materials for green phosphorescent OLEDs with the device configuration, [ITO/ PEDOT:PSS/Emitting layer/TPBi/CsF/Al]. All the devices emitted typical green light with high luminance and had low turn-on voltages along with good luminous efficiencies which were further improved by adjusting charge balance using PBD, as a co-host. The basic characteristics and the preliminary OLED results showed the usefulness of our new materials, and this kind of 1-/1,8-substitution of carbazole would open a new way of materials design.
Efficient red phosphorescent OLEDs employing carbazole-based materials as the emitting host
Dyes and Pigments, 2015
We report on the synthesis and characterization of a new series of electro-active carbazole-based compounds. The derivatives are thermally stable amorphous materials with glass transition temperatures in the range of 54e93 C. Electron photoemission spectra of thin layers of the materials show ionization potential in the range of 5.4e5.5 eV. The carbazole-based derivatives are fully characterized and their spectroscopic properties are determined by absorption and photoluminescence. All developed materials and commonly-used tris(4-carbazoyl-9-ylphenyl)amine (TCTA) were used as hosts in red phosphorescent organic light-emitting diodes (OLEDs) for comparison. Results indicate that a device with 3-[bis(9-ethylcarbazol-3-yl)methyl]-9-hexylcarbazole exhibited superior performance with peak efficiencies of 8.4%, 5.3 cd/A and 5.5 lm/W.
Journal of Physical Organic Chemistry, 2017
New 2-(4′-9H-carbazole-9-yl)-styryl-1H-phenathro[9,10-d]imidazole-1-yl)benzonitrile (SPICN-Cz) and 4-(2-(4-(diphenylamino)phenyl-styryl-1H-phenathro[9,10-d]imidazole-1-yl)benzonitrile (SPICN-TPA) have been synthesised, and their photophysical, electrochemical, and electroluminescent properties were analysed in comparison with their cyano-free parent compounds, SPI-Cz, and SPI-TPA. Solvatochromic effects show the transformation of an excited state character from locally excited (LE) state to charge transfer (CT) state. Using time-dependent density functional theory calculation, the excited state properties of these donor-acceptor blue emissive materials have been analysed. Their excited state properties have been tuned by replacing the strong donor triphenylamine to weak donor carbazole to achieve the combination of high photoluminance efficiency locally excited (LE) component and high exciton-utilizing CT component in one excited state. Hybridization processes between LE and CT components of SPICN-Cz and SPICN-TPA in the emissive state have been discussed. The nondoped organic light emitting diode device based on SPICN-Cz exhibit better electroluminescent performances than those of SPICN-TPA-based device: high external quantum efficiency of 2.58 %, current efficiency of 2.90 cd A-1 , and power efficiency of 2.26 lm W-1 with Commission Internationale de l'Éclairage (CIE) coordinates of (0.15, 0.12). The excited state modulation and the composition of LE and CT states in the donor-acceptor system could be useful to design low-cost, high-efficiency fluorescent organic light emitting diode materials.
Organic Electronics, 2006
Three new oxadiazole substituted carbazole derivatives 9-{4-[5-(4-tert-butylphenyl)-[1,3,4] oxadiazol-2-yl]-benzyl}-9 H-carbazole (t-CmOxa), 9-[4-5-phenyl-[1,3,4]oxadiazol-2-yl-benzyl]-9H-carbazole (p-CmOxa) and 9- [4-5-biphenyl-[1,3,4] oxadiazol-2-yl-benzyl]-9H-carbazole (d-CmOxa) were successfully synthesized and characterized by spectroscopy (NMR, UV-vis, mass spectrum and photoluminescence) and cyclic voltammetry measurements. Employing t-CmOxa as a host and Ir(DBQ) 2 (acac) (DBQ = dibenzo[f,h]quinoxaline, acac = acetylacetonate) as the dopant emitter, OLEDs with structures of ITO/NPB(30 nm)/Ir(DBQ) 2 (acac): t-CmOxa (30 nm, x%)/Alq 3 (30 nm)/Mg 0.9 :Ag 0.1 were fabricated without using BCP as the hole blocking layer. Red emission was obtained with CIE coordinates (x = 0.66, and y = 0.34) at 5 V and a very high external electroluminescent (EL) quantum efficiency of 9.5 ± 0.1%, and an energy conversion efficiency of 9.9 ± 0.1 lm/W were achieved for the device when the doping concentration x is equal to 4%.
Carbazole–pyrene derivatives for undoped organic light-emitting devices
Organic Electronics, 2011
Two carbazole-pyrene derivatives, namely 3,6-dipyrenyl-9-(4 0-tert-butylphenyl) carbazole (BPyC) and 3,6-dipyrenyl-9-(4 0-pyrenylphenyl) carbazole (TPyC), have been designed and synthesized for application in organic light-emitting devices (OLEDs). While the two compounds have similar chemical structures and photoluminescent properties, OLEDs based on them show distinct electroluminescence (EL) spectra. The BPyC-based devices show a single peak saturated blue emission with CIE coordinates of (0.15, 0.18); whereas the TPyC-based devices exhibit two emission peaks at blue and yellow hues with CIE coordinates of (0.22, 0.29). The difference in their EL spectra is attributed to the substitution of the t-butyl unit of BPyC with a pyrenyl group to form TPyC, which effectively increases the electron-donating property and results in exciplex formation at its interface with the electron-accepting TPBI. A high external quantum efficiency of 3.11% is achieved in the TPyC-based devices. Influences of chemical structure and fluorescent quantum yield on the efficiency of exciplex emission are discussed.
Synthetic Metals, 2011
Phenyl or naphthyl substituted 9-(2,2-diphenylvinyl)carbazoles were synthesized by the multi-step synthetic route. The materials were examined by various techniques including thermogravimetry, differential scanning calorimetry, and electron photoemission technique. These derivatives were also tested as hole-transporting materials in bilayer OLEDs with Alq 3 as the emitter. The devices exhibited promising overall performance with a turn-on voltage of 3.2 V, a maximal photometric efficiency of about 4.8 cd/A and maximum brightness of 12,400-13,100 cd/m 2 .