Abstract A group of novel thieno‐[3,4‐ b ]‐pyrazine‐cored molecules containing polyphenyl dendrons with or without arylamino or carbazolyl surface groups ( DTP , N‐DTP and C‐DTP ) are synthesized and investigated. They are characterized by extra large Stokes shifts of over 250 nm. In addition, to provide the site‐isolation effect on the planar emissive core, the bulky dendrons enable these molecules to be solution processible. The peripheral carbazolyl or arylamino units facilitate the hole transporting ability in the neat films of these molecules. These dendritic materials are used as a non‐doped emitting layer to fabricate organic light‐emitting diodes (OLEDs) using a spin coating technique and saturated red emission is obtained. The dendritic molecules with arylamino or carbazolyl surface groups ( N‐DTP and C‐DTP ) exhibit a brightness of 1020 cd m −2 and a luminous efficiency of 0.6 cd A −1 , both higher than the dendritic analog without the surface functional groups ( DTP ), even superior to the small molecular reference compound which fails to transmit pure red emission under identical conditions. This performance is also comparable with that from vacuum deposited thieno‐[3,4‐ b ]‐pyrazine‐based counterparts and that for some other solution processible red fluorescent dendrimers. This is the first example of solution processible thieno‐[3,4‐ b ]‐pyrazine derivatives for OLED applications. magnified image
Two novel durene-containing molecules, 1,4-bis-[4-(9-carbazolyl)-phenyl]-durene (CPD) and 1,4-bis-{4-[9-(3,6-(di-tert-butyl)carbazoyl)]-phenyl}-durene (t-BuCPD), which are derived from 4,4′-bis(9-carbazolyl)biphenyl (CBP) by inserting durene in its biphenyl core, are designed and synthesized for use as host materials for blue phosphors in organic light-emitting diodes (OLEDs). Inserting durene in biphenyl causes a right-angle torsion between the durene and the adjacent phenyl groups due to the strong steric hindrance effect of the durene group, confining the effective π-conjugation on only one carbazole and one phenyl and increasing the triplet energies of CPD and t-BuCPD to over 3.0 eV. These durene-decorated molecules show higher thermal stabilities than many other CBP derivatives. Blue phosphorescent OLEDs were fabricated using CPD and t-BuCPD as triplet hosts and traditional iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (Firpic) as a dopant and excellent performances were achieved. In particular, peak efficiencies of 26.2 cd A−1 and 14.8 lm W−1 were realized when CPD was used as both a host and exciton-blocking material. This is the first report using durene to tune the triplet energy levels of phosphorescent host materials.
Abstract Herein, a design strategy is explored for thermally activated delayed fluorescence (TADF) materials by employing the meta ‐linkage of the spiral‐donors 10H‐spiro[acridine‐9,9'‐thioxanthene] (DspiroS) and 10',10'‐dimethyl‐10H,10'H‐spiro[acridine‐9,9'‐anthracene] (DspiroAc) to the robust acceptor 2,4,6‐triphenyl‐1,3,5‐triazine (TRZ). Two distinct TADF materials, m‐DspiroS‐TRZ and m‐DspiroAc‐TRZ, exhibiting unique photophysical properties and performance characteristics were synthesized. Interestingly, even subtle modifications in the molecular architecture can significantly impact the organization of materials in their aggregated state, thereby governing photophysical properties and inducing corresponding alterations in photoelectric characteristics. Notably, m ‐DspiroS‐TRZ exhibits superior photophysical properties and exciton dynamics data, achieving a high photoluminescence quantum yield (PLQY) value of up to 95.9% and a rapid reverse intersystem crossing (RISC) rate (𝒌 𝑹𝑰𝑺𝑪 ) of 1.0 × 10 6 s −1 . This positions m ‐DspiroS‐TRZ as a potentially excellent terminal emissive and sensitizing host material, inspiring further exploration of its applications in electroluminescence. Consequently, TADF organic light‐emitting device (TADF‐OLED) and TADF‐sensitized fluorescence (TSF‐OLED) based on m ‐DspiroS‐TRZ have achieved maximum external quantum efficiencies (EQEs) of 31.8% and 34.5%, respectively, demonstrating the significant versatile potential of m ‐DspiroS‐TRZ.
The effects of fluorophenyl substituents on the photoluminescence, redox properties, and oxygen sensing behaviors of the cyclometalated Pt(II) complexes are reported. The Pt(II) complexes with fluorophenyl substituents at the para position on the phenyl ring of 2-phenylpyridine (ppy) exhibit higher oxygen sensitivities than those at the meta position. Photodegradation tests demonstrate that the introduction of fluorophenyl substituents can strongly improve the photostability of cyclometalated Pt(II) complexes. Fast response and recovery times of oxygen sensing films are obtained in 3.0 s on going from 0% O2 to 100% O2 and in 4.0 s on going from 100% O2 to 0% O2 (95% recovery of the luminescence), respectively. The oxygen sensing films show excellent operational stability in 4000 s saturation O2/N2 cycles, which meets the requirement of monitoring molecular oxygen in real time.
As a new technology for flat-panel displays and general lighting sources, solution-processed phosphorescent organic light-emitting diodes (PhOLEDs) unfurl a bright future, due to their merits of high quantum efficiency and easy fabrication. In recent years, great progress has been made in the device performance of solution-processed PhOLEDs, by developing both high-efficiency organometallic phosphors and novel solution-processable organic host materials. This review highlights recently developed organic host materials for triplet guest emitters in solution-processed PhOLEDs. The solution-processable host materials are classified into three types – small molecule, dendrimer, and polymer – according to their molecular architecture and molecular weight. The material design concept and the relationships between the molecular structure, material properties and device performance are the focus of this discussion. A future strategy for the development of high-performance solution-processed host materials is proposed.
By tuning the peripheral groups on carbazole to increase the donor strength, the Δ E ST , Δ E TT and SOC are simultaneously optimized to facilitate the RISC and radiative transition. The EQE of 17.4% with CIE (0.15, 0.11) is realized in OLEDs.
Organic photovoltaic devices using starburst amine PCATA as the electron donor layer gave a quantum efficiency of up to 21.7% at short-circuit conditions, which is higher than those reported for UV-sensitive organic PV cells.
Novel fluorene based deep-blue-emitting molecules with naphthylanthracene endcaps, namely 2,7-di(10-naphthylanthracene-9-yl)-9,9-dioctylfluorene (NAF1) and 7,7′-di(10-naphthylanthracene-9-yl)-9,9,9′,9′-tetraoctyl-2,2′-bifluorene (NAF2), are synthesized by a Suzuki cross-coupling reaction. These materials exhibit excellent thermal and amorphous stabilities, and high fluorescence quantum yield of over 70%. Organic light-emitting devices (OLEDs) using NAF1 or NAF2 as non-doped emitter exhibit bright deep blue electroluminescence with CIE coordinates of (0.15, 0.13) for NAF1, (0.16, 0.13) for NAF2. A maximum power efficiency of 2.2 lm W−1 (4.04 cd A−1, 4.04%) is achieved for NAF1, which is among the highest values ever reported for deep-blue fluorescent OLEDs. A further improved coordinates of (0.15, 0.09) with efficiencies of 3.56 cd A−1 and 2.10 lm W−1 are achieved for NAF1 upon tuning device thickness, which are also among the best data for non-doped deep blue fluorescent OLEDs with a CIE coordinate of y < 0.1. NAF1 serves as excellent host emitter when doped with an orange fluorophore (4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran, DCJTB). Upon careful tuning the doping level, the two-emitting-component (NAF1 : DCJTB) OLED realizes efficient white light emission with a power efficiency of 3.01 lm W−1 (7.66 cd A−1), a brightness of 12090 cd m−2, and a standard white light coordinates of (0.33, 0.33). This performance is among the best results ever reported for two-emitting-component white OLEDs based on fluorescent materials.
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