Highly Active Cross-Metathesis of Tetrafluoroethylene with a Seven-Membered N-Heterocyclic-Carbene-Ruthenium Catalyst.

A drastic increase in catalyst turnover number (TON) was accomplished in the cross-metathesis of tetrafluoroethylene (TFE) and vinyl ethers. Under a continuous flow of TFE, catalyst Ru7, which contains a seven-membered N-heterocyclic carbene (NHC) ligand, reached a TON of 4100; this is 2 orders of magnitude higher than the highest hitherto reported value. Mechanistic studies revealed that the expanded NHC successfully destabilizes the stable intermediates with a difluorocarbene structure, which strongly promotes the reaction.

Molecular Design Based on Donor-Weak Donor Scaffold for Blue Thermally-Activated Delayed Fluorescence Designed by Combinatorial DFT Calculations.

Quantum chemical calculations are necessary to develop advanced emitter materials showing thermally-activated delayed fluorescence (TADF) for organic light-emitting diodes (OLEDs). However, calculation costs become problematic when more accurate functionals were used, therefore it is judicious to use a multimethod approach for efficiency. Here we employed combinatorial chemistry in silico to develop the deep blue TADF materials with a new concept of homo-junction design. The homo-junction materials containing TADF candidates designed by calculation were synthesized and analyzed. We found that these materials showed the emission from charge transfer (CT) state, and the clear delayed emission was provided in solid state. Because the homo-junction TADF materials showed three exponential decayed emission in solid state, we employed novel four-state kinetic analysis.

Trifluoromethane modification of thermally activated delayed fluorescence molecules for high-efficiency blue organic light-emitting diodes.

Highly efficient blue and green thermally activated delayed fluorescence (TADF) molecules bearing trifluoromethane-modified carbazole groups were developed. The trifluoromethane groups on carbazole induced blue-shifted emission and improved the photoluminescence quantum yield. The photostability of the TADF molecules was strongly related to the modification position of trifluoromethane on carbazole.

Long-lived efficient delayed fluorescence organic light-emitting diodes using n-type hosts.

Organic light-emitting diodes have become a mainstream display technology because of their desirable features. Third-generation electroluminescent devices that emit light through a mechanism called thermally activated delayed fluorescence are currently garnering much attention. However, unsatisfactory device stability is still an unresolved issue in this field. Here we demonstrate that electron-transporting n-type hosts, which typically include an acceptor moiety in their chemical structure, have the intrinsic ability to balance the charge fluxes and broaden the recombination zone in delayed fluorescence organic electroluminescent devices, while at the same time preventing the formation of high-energy excitons. The n-type hosts lengthen the lifetimes of green and blue delayed fluorescence devices by > 30 and 1000 times, respectively. Our results indicate that n-type hosts are suitable to realize stable delayed fluorescence organic electroluminescent devices.

Donor-σ-Acceptor Motifs: Thermally Activated Delayed Fluorescence Emitters with Dual Upconversion.

A family of organic emitters with a donor-σ-acceptor (D-σ-A) motif is presented. Owing to the weakly coupled D-σ-A intramolecular charge-transfer state, a transition from the localized excited triplet state (3 LE) and charge-transfer triplet state (3 CT) to the charge-transfer singlet state (1 CT) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200-400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D-σ-A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes.

Highly Efficient Thermally Activated Delayed Fluorescence from an Excited-State Intramolecular Proton Transfer System.

Thermally activated delayed fluorescence (TADF) materials have shown great potential for highly efficient organic light-emitting diodes (OLEDs). While the current molecular design of TADF materials primarily focuses on combining donor and acceptor units, we present a novel system based on the use of excited-state intramolecular proton transfer (ESIPT) to achieve efficient TADF without relying on the well-established donor-acceptor scheme. In an appropriately designed acridone-based compound with intramolecular hydrogen bonding, ESIPT leads to separation of the highest occupied and lowest unoccupied molecular orbitals, resulting in TADF emission with a photoluminescence quantum yield of nearly 60%. High external electroluminescence quantum efficiencies of up to 14% in OLEDs using this emitter prove that efficient triplet harvesting is possible with ESIPT-based TADF materials. This work will expand and accelerate the development of a wide variety of TADF materials for high performance OLEDs.