Molecular Design Strategy of Thermally Activated Delayed Fluorescent Emitters Using CN‐Substituted Imidazopyrazine as a New Electron‐Accepting Unit

Abstract

Thermally activated delayed fluorescence( TADF)based organic light-emitting diodes (OLEDs) have attracted enormous attention recently due to their capabilityt or eplace conventionalp hosphorescent organic light-emitting diodes for practical applications.I nt his work, an ewly designed CN-substituted imidazopyrazine moiety was utilized as an electron-accepting unit in aT ADF emitter.T wo TADF emitters, 8-(3-cyano-4-(9,9-dimethylacridin-10(9H)-yl)phenyl)-2-phenylimidazo[1,2-a]pyrazine-3-carbonitrile (Ac-CNImPyr) and 8-(3-cyano-4-(10H-phenoxazin-10-yl)phenyl)-2-phenylimidazo[1,2-a]pyrazine-3-carbonitrile (PXZ-CNImPyr), were developed based on the CN-substituted imidazopyrazine ac-ceptor combined with acridine and phenoxazine donor,r espectively.ACN-substituted phenyls pacerw as introduced between the donor and acceptor for as ufficiently small singlet-triplet energy gap (DE ST )a nd molecular orbitalm anagement. Small DE ST of 0.07 eV was achieved for the phenoxazine donor-based PXZ-CNImPyr emitter.A sar esult,a no rganic light-emitting diode based on the PXZ-CNImPyr emitter exhibited ah igh externalq uantum efficiency of up to 12.7 %, which surpassed the EQE limit of common fluorescent emitters. Hence, the CN-modified imidazopyrazine unit can be introduced asanew acceptor for further modifications to develop efficient TADF-based OLEDs.[a] Dr.

Isomer engineering of dipyrido[3,2-a:3′,4′-c]phenazine-acceptor-based red thermally activated delayed fluorescent emitters

“…Organic-emitter-based thermally activated delayed fluorescent (TADF)-OLEDs are considered competent alternatives to Ph-OLEDs, as internal quantum efficiencies of up to 100% are achievable in both cases. [7][8][9][10][11][12][13] Compared to precious-metalbased phosphorescent emitters, TADF emitters are inexpensive and allow for greater diversity in their design. Organic materials with a small singlet-triplet energy gap (DE ST ) are capable of converting non-radiative triplet excitons to radiative singlet excitons via a reverse intersystem crossing (RISC) process.…”

Singlet–triplet splitting energy management for thermally activated delayed fluorescence emitters: up-conversion of acceptor triplet into charge transfer singlet state

“…[1][2][3][4][5] In order to achieve efficient rISC and thus TADF, TADF emitters should be designed to possess small singlet-triplet splitting energy (DE ST ) between the singlet state (S 1 ) and the triplet state (T 1 ). [6][7][8] In this regard, many studies revealed that a donor-acceptor (D-A) design with a large twisting angle is the best universal strategy. Evidently, such a strategy can effectively separate the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs), and thus achieve the minimizing exchange integral and consequently a small DE ST .…”

4-(Aryl)-Benzo[4,5]imidazo[1,2-a]pyrimidine-3-Carbonitrile-Based Fluorophores: Povarov Reaction-Based Synthesis, Photophysical Studies, and DFT Calculations

“…The functionalization of the imidazole-containing domain with a strongly electron-withdrawing cyano-group and a reduced singlet-triplet energy gap, on the other hand, has received special attention as a universal and appealing strategy for creating AIE-active fluorophores, including those with thermally activated delayed fluorescence (TADF) [39]. For instance, the authors of [40] recently developed TADF materials with C3-functionalized cyano-group 2-phenylimidazopyrazine as an acceptor unit linked to either acridine or phenoxazine donor units, and for these fluorophores an EQE of about 12.7% was achieved. In addition, the use of 2-phenylimidazo[1,2-a]pyridine containing cyano-group as an acceptor has been reported as a tool for designing dark blue emitters with a relatively high fluorescence quantum yield [36,41].…”