Asymmetrical-Dendronized TADF Emitters for Efficient Non-doped Solution-Processed OLEDs by Eliminating Degenerate Excited States and Creating Solely Thermal Equilibrium Routes.

The mechanism of thermally activated delayed fluorescence (TADF) in dendrimers is not clear. We report that fully-conjugated or fully-nonconjugated structures cause unwanted degenerate excited states due to multiple identical dendrons, which limit their TADF efficiency. We have synthesized asymmetrical "half-dendronized" and "half-dendronized-half-encapsulated" emitters. By eliminating degenerate excited states, the triplet locally excited state is ≥0.3 eV above the lowest triplet charge-transfer state, assuring a solely thermal equilibrium route for an effective spin-flip process. The isolated encapsulating tricarbazole unit can protect the TADF unit, reducing nonradiative decay and enhancing TADF performance. Non-doped solution-processed devices reach a high external quantum efficiency (EQEmax ) of 24.0 % (65.9 cd A-1 , 59.2 lm W-1 ) with CIE coordinates of (0.24, 0.45) with a low efficiency roll-off and EQEs of 23.6 % and 21.3 % at 100 and 500 cd m-2 .

Photoluminescent Behaviors of Thermally Activated Delayed Fluorescence Polymeric Emitters in Nanofibers.

Anisotropic 1D nanostructures with high surface-area-to-volume ratio display the enhanced optoelectronic properties of light-emitting compounds compared to bulk or 2D systems. To study the effect of nanometer-constrained space on photoluminescent behavior of thermally activated delayed fluorescence (TADF) polymeric emitters, electrospinning technique is used to produce nanofibers of TADF emitters. Herein, two TADF polymer (P1 and P3) nanofibers with 90% polyacrylonitrile (PAN) are fabricated and their photophysical properties are studied and compared with their spin-coated film counterparts. The distinguishing polarized photoluminescencent properties of P1/PAN or P3/PAN electrospun nanofibers are obtained due to high orientation degree and superior molecular arrangement. Moreover, the better TADF properties in nanofibers can be observed comparing with their spin-coated films, including longer-lived excited states, higher photoluminescence quantum efficiency, lower internal conversion decay rate, and higher reverse intersystem crossing rate constant.

Synthesis and Cyclization-Induced Charge Transfer of Rectangular Bisterthiophenesiloxanes.

Cyclization-modified terthiophene displays the change of emission behavior from locally excited (LE) to the intramolecular charge transfer (ICT) state. The rectangular bisterthiophenesiloxanes (DSiTh) was successfully prepared by π-π-stacking-aided hydrogen-bonding interactions. Cyclization-induced ICT in DSiTh could be observed, which was confirmed by absorption spectra, fluorescence spectra, and quantum chemistry analysis. The cyclization produces a strong intramolecular electron redistribution of a highly packed π-conjugated terthiophene. Thus, a distinctive variation of the dipole moment and a through-space ICT happen.

Development of a UPLC-MS/MS method for determination of a dual EZH1/2 inhibitor UNC1999 in rat plasma.

Aim: We aimed to establish and validate a simple and sensitive UPLC-MS/MS method for the determination of UNC1999, a dual inhibitor against EZH1 and EZH2 in plasma samples. Materials & methods: UNC1999 in rat plasma was processed with protein precipitation method and then separated on a C18 column and detected under positive ionization mode. The method presented good linearity over the range of 1.0-2000 ng/ml with good accuracy and precision. UNC1999 was absorbed slowly and achieved a maximum concentration of 118.8 ± 12.0 ng/ml 1.5 h after oral administration. Conclusion: The method provides a favorable character in selectivity, linearity, accuracy, precision, recovery, matrix effects and stabilities and was suitable for describing the pharmacokinetic profile of UNC1999.

Blue Phosphorescence and Hyperluminescence Generated from Imidazo[4,5-b]pyridin-2-ylidene-Based Iridium(III) Phosphors.

Four isomeric, homoleptic iridium(III) metal complexes bearing 5-(trifluoromethyl)imidazo[4,5-b]pyridin-2-ylidene and 6-(trifluoromethyl)imidazo[4,5-b]pyridin-2-ylidene-based cyclometalating chelates are successfully synthesized. The meridional isomers can be converted to facial isomers through acid induced isomerization. The m-isomers display a relatively broadened and red-shifted emission, while f-isomers exhibit narrowed blue emission band, together with higher photoluminescent quantum yields and reduced radiative lifetime relative to the mer-counterparts. Maximum external quantum efficiencies of 13.5% and 22.8% are achieved for the electrophosphorescent devices based on f-tpb1 and m-tpb1 as dopant emitter together with CIE coordinates of (0.15, 0.23) and (0.22, 0.45), respectively. By using f-tpb1 as the sensitizing phosphor and t-DABNA as thermally activated delayed fluorescence (TADF) terminal emitter, hyperluminescent OLEDs are successfully fabricated, giving high efficiency of 29.6%, full width at half maximum (FWHM) of 30 nm, and CIE coordinates of (0.13, 0.11), confirming the efficient Förster resonance energy transfer (FRET) process.

Thermally Activated Delayed Fluorescence Pendant Copolymers with Electron- and Hole-Transporting Spacers.

To study the effect of hole- and electron-transporting spacers in copolymers on the thermally activated delayed fluorescence (TADF) properties and device efficiency of copolymers, two series of copolymers PCzPT-x and POPT-x have been designed and synthesized successfully. In these copolymers, 2-(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide units give green-yellow TADF, while hole-transporting 9-(4-vinylphenyl)-9H-carbazole units or electron-transporting diphenyl(4-vinylphenyl)phosphine oxide act as spacers or hosts. Their thermal, electrochemical, photophysical, and electroluminescent properties and theoretical calculations are systematically investigated to illustrate the relationships between molecular structures and photophysical properties. By optimizing the upconversion and radiative decay rate and managing the energy transfer, a green-yellow device based on POPT-25 achieves a maximum external quantum efficiency of 5.2%, a current efficiency of 16.8 cd/A, and a power efficiency of 7.8 lm/W with CIE coordinates of (0.36, 0.50). Moreover, an external quantum efficiency of 3.5% at the practical luminescence of 100 cd/m2 is obtained.

Pyridylpyrazole N

A series of blue iridium(iii) complexes (12-15) comprising sulfonyl-functionalised phenylpyridyl cyclometalating ligands and pyridylpyrazole N^N ligands are reported, with an X-ray crystal structure obtained for 12. The complexes are highly emissive with photoluminescence quantum yields of 0.52-0.70 in dichloromethane solutions: two of the complexes (12 and 14) show emissions at λ 457 nm which is considerably blue-shifted compared to the archetypal blue emitter FIrpic (λmax 468 nm). The short excited state lifetimes (1.8-3.3 µs) and spectral profiles are consistent with phosphorescence from a mixture of ligand-centred and MLCT excited states. Density functional (DFT) and time dependent DFT (TD-DFT) calculations are in agreement with the electrochemical properties and the blue phosphorescence of the complexes. The additional mesityl substituent on the pyridylpyrazole ligand of 12 and 13 enhances the solubility of the complexes facilitating thin film formation by solution processing. Phosphorescent organic light-emitting diodes (PhOLEDs) have been fabricated using 12 or 13 in a solution-processed single-emitting layer using either poly(vinylcarbazole) (PVK) or 1,3-bis(N-carbazolyl)benzene (mCP) as host. The most blue-shifted electroluminescence (λ 460 nm, CIEx,y 0.15, 0.21) is obtained for an OLED containing complex 12 and mCP, with a brightness of 5400 cd m-2 at 10 V which is high for PhOLEDs with similar blue CIE coordinates using a solution-processed emitter layer.