Utilizing a Spiro TADF Moiety as a Functional Electron Donor in TADF Molecular Design toward Efficient “Multichannel” Reverse Intersystem Crossing

Abstract

Designing thermally activated delayed fluorescence (TADF) materials with an efficient reverse intersystem crossing (RISC) process is regarded as the key to actualize efficient organic light-emitting diodes (OLEDs) with low efficiency roll-off. Herein, a novel molecular design strategy is reported where a typical TADF material 10-phenyl-10H, 10′H-spiro[acridine-9, 9′-anthracen]-10′-one (ACRSA) is utilized as a functional electron donor to design TADF materials of 2,4,6-triphenyl-1,3,5-triazine(TRZ)-p-ACRSA and TRZ-m-ACRSA. It is unique that the intramolecular charge transfer of the ACRSA moiety and the intramolecular and through-space intermolecular charge transfer between the TRZ and ACRSA moieties, provide a "multichannel" effect to enhance the rate of the reverse intersystem crossing process (k risc ) exceeding 10 −6 s −1 . TADF OLEDs based on TRZ-p-ACRSA as an emitter show a maximum external quantum efficiency (EQE) of 28% with reduced efficiency roll-off (EQEs of 27.5% and 22.1% at 100 and 1000 cd m −2 , respectively). Yellow phosphorescent OLEDs utilizing TRZ-p-ACRSA as a host material show record-high EQE of 25.5% and power efficiency of 115 lm W −1 , while phosphorescent OLEDs based on TRZ-m-ACRSA show further lower efficiency roll-off with EQEs of 25.2%, 24.3%, and 21.5% at 100, 1000, and 10 000 cd m −2 , respectively.being consistent with the El-Sayed rule of intersystem crossing (ISC) process, when the natures of 1 CT and 3 CT are different, the SOC between 1 CT and 3 CT might be efficient as well. [2] More importantly, avoiding dual emission phenomenon, which caused by conformational transforming brought by flexible moieties, is considered as the first priority of TADF molecular design strategy. [9] Conformational transforming not only results in energy loss, but also limits the triplet exciton utilization because not all possible conformations have potential to achieve TADF phenomenon. [10] On the basis of this understanding, the key to design TADF

Tris(triazolo)triazine-based emitters for solution-processed blue thermally activated delayed fluorescence organic light-emitting diodes

“…Typically, a small DE ST is achieved by the spatial separation of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The classic design strategies are based on the combination of donor and acceptor groups and their small electronic coupling either via (1) a twisted intramolecular charge transfer [6][7][8][9][10][11] transition, (2) a through-space charge-transfer transition, 7,8,12 (3) a spiroconjugation charge transfer transition 13,14 or (4) an alternating HOMO/LUMO distribution in p,n-doped polycyclic aromatic hydrocarbons, termed a multi-resonance TADF transition. 2,[15][16][17][18] By employing solution-based processing techniques, [19][20][21] large-area OLEDs becomes simpler and more cost-efficient to fabricate.…”

Efficient Orange–Red Delayed Fluorescence Organic Light‐Emitting Diodes with External Quantum Efficiency over 26%

“…Density functional theory (DFT) and time-dependent DFT calculations were carried out by Gaussian 09 program with B3LYP/6-31G(d) basis sets to investigate the FMOs, HOMO/ LUMO levels, ground states, and excited states properties of BP derivatives (i.e., 1PXZ-BP, 2PXZ-BP, and 3PXZ-BP) in toluene solution. [2,5] As shown in Figure 1, all the dihedral angles between PXZ donor and BP acceptor are above 80° for three pre-twisted molecules in the optimized geometries. Moreover, the FMOs of all three compounds are almost completely separated, in which the LUMO levels are localized at the BP unit but the HOMO levels are mainly localized at the electron-donating PXZ moiety with a slight extent on the adjacent benzene ring.…”

“…Organic light-emitting diodes (OLEDs) have become a leading display technology due to their steadily improved efficiency and unique features such as fascinating flexibility, lightweight, no turn-on delay, superior color gamut, and wide viewing angle. [1][2][3][4][5][6] The key electroluminescent (EL) materials in OELDs are traditional fluorescent and phosphorescent materials. Fluorescent materials are inefficient with the maximum internal quantum efficiency (IQE) of only 25%, while phos-for orange-red/red TADF materials, since this PLQYs value can decrease with respect to the increase in emission wavelength in view of energy-gap law.…”

Multichannel Effect of Triplet Excitons for Highly Efficient Green and Red Phosphorescent OLEDs

“…That indicates more triplet excitons can be converted into singlet excited state and then transferred to emitters. [ 36,37 ] Therefore, the additional fast RISC process is critical to reduce the density of triplet excitons and to prevent TTA. Thus the TTA was effectively decreased in our green and red PhOLEDs, which is helpful to improve the performance of PhOLEDs.…”