Harnessing a New Co-Host System and Low Concentration of New TADF Emitters Equipped with Trifluoromethyl- and Cyano-Substituted Benzene as Core for High-Efficiency Blue OLEDs.

A strategic approach combining a new co-host system and low concentration of new thermally activated delayed fluorescence (TADF) emitters to make efficient blue TADF organic light-emitting diode (OLED) was developed. The benchmark TADF molecule, 4CzIPN, was adopted as a probe to examine the feasibility of a co-host composing of a hole transporter SimCP and an electron transporter oCF3-T2T. As a result, a sky blue device with 1 wt % 4CzIPN doped in SimCP:oCF3-T2T co-host exhibited 100% energy transfer and achieved a high external quantum efficiency (EQE) up to 26.1%. Importantly, this device showed a limited efficiency rolloff with an EQE of 24% at 1000 cd m-2. To further shift the emission toward blue, three new TADF molecules, 4CzIPN-CF3, 3CzIPN-H-CF3, and 3CzIPN-CF3, modified either by lowering the electron-withdrawing ability of the acceptor group or by reducing the number of carbazole donors of 4CzIPN, have been synthesized and characterized. Among them, 4CzIPN-CF3 and 3CzIPN-H-CF3 display hypsochromic shift emissions compared to that of 4CzIPN. These new compounds were then explored for their potential applications as TADF emitters. Blue TADF OLEDs with 1 wt % of 4CzIPN-CF3 and 3CzIPN-H-CF3 dispersed in SimCP:oCF3-T2T co-host achieved EQEs of 23.1 and 16.5% and retained high EQEs of 20.9 and 14.7% at 1000 cd m-2, respectively.

Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D-D'-A TADF Emitters.

Understanding the excited-state dynamics and conformational relaxation in thermally activated delayed fluorescence (TADF) molecules, including conformations that potentially support intramolecular through-space charge transfer, can open new avenues for TADF molecular design as well as elucidate complex photophysical pathways in structurally complex molecules. Emissive molecules comprising a donor (triphenylamine, TPA) and an acceptor (triphenyltriazine, TRZ) bridged by a second donor (9,9-dimethyl-9-10-dihydroacridin, DMAC, or phenoxazine, PXZ) are synthesized and characterized. In solution, the flexibility of the sp3-hybridized carbon atom in DMAC of DMAC-TPA-TRZ, compared to the rigid PXZ, allows significant conformational reorganization, giving rise to multiple charge-transfer excited states. As a result of such a reorganization, the TRZ and TPA moieties become cofacially aligned, driven by a strong dipole-dipole attraction between the TPA and TRZ units, forming a weakly charge-transfer dimer state, in stark contrast to the case of PXZ-TPA-TRZ where the rigid PXZ bridge only supports a single PXZ-TRZ charge transfer (CT) state. The low-energy TPA-TRZ dimer is found to have a high-energy dimer local triplet state, which quenches delayed emission because the resultant singlet CT local triplet energy gap is too large to mediate efficient reverse intersystem crossing. However, organic light-emitting diodes using PXZ-TPA-TRZ as an emitting dopant resulted in external quantum efficiency as high as 22%, more than two times higher than that of DMAC-TPA-TRZ-based device, showing the impact that such intramolecular reorganization and donor-acceptor dimerization have on TADF performance.

Iron-catalyzed synthesis of thioesters from thiols and aldehydes in water.

The preparation of thioesters through the iron-catalyzed coupling reaction of thiols with aldehydes is described. The reactions were carried out by using tert-butyl hydroperoxide (TBHP) as an oxidant and water as a solvent in most cases. This system is compatible with a variety of functional groups.

Manganese-catalyzed cross-coupling of thiols with aryl iodides.

A manganese-catalyzed cross-coupling reaction of thiols with aryl iodides, furnishing aryl thioethers in good to excellent yields has been reported; the system shows good functional group tolerance and enables the sterically demanding aryl iodides to couple with thiols.

Highly regioselective synthesis of aryl chalcogenides through C-H functionalization of arenes.

We report here the regioselective synthesis of aryl chalcogenides through the iridium-catalyzed meta C-H borylation followed by copper-catalyzed C-S coupling reaction with chalcogenide sources in one pot, giving the 3,5-disubstituted aryl chalcogenides with high regioselectivity and good yields.