Abstract
Organic materials with aggregation‐induced delayed fluorescence (AIDF) have exhibited impressive merits for improving electroluminescence efficiency and decreasing efficiency roll‐off of nondoped organic light‐emitting diodes (OLEDs). However, the lack of comprehensive insights into the underlying mechanism may impede further development and application of AIDF materials. Herein, AIDF materials consisting of benzoyl serving as an electron acceptor, and phenoxazine and fluorene derivatives as electron donors are reported. They display greatly enhanced fluorescence with increased delayed component upon aggregate formation. Experimental and theoretical investigations reveal that this AIDF phenomenon can be rationally ascribed to the suppression of internal conversion and the promotion of intersystem crossing in solid. Moreover, the theoretical calculations disclose that the efficient solid‐state delayed fluorescence originates from the higher energy electronic excited state (e.g., S2) rather than the lowest energy‐excited state (S1), demonstrating an anti‐Kasha behavior. The excellent AIDF property allows high exciton utilization and thus superb performance of OLEDs using these new materials as light‐emitting layers.
Highlights
(TADF) emitters that are able to fully harefficiency and decreasing efficiency roll-off of nondoped organic light-emitting diodes (OLEDs)
We have developed a series of new AIDF materials by combining an electron-withdrawing benzoyl core and the electron-donating PXZ and fluorene derivatives
These AIDF materials can be readily synthesized with high yields so that they are applicable for the large-scale commercial applications
Summary
The new emitters DMF-BP-PXZ, DPF-BP-PXZ, and SBF-BP-PXZ were prepared according to the synthetic routes involving two-steps reactions with high yields as described in Supporting Information. The molecular structures were confirmed by NMR and high-resolution mass spectrometry. They are highly soluble in common organic solvents including tetrahydrofuran (THF), dichloromethane, chloroform, toluene, etc., but insoluble in water and ethanol. The high decomposition temperatures (Td, corresponding to 5% weight loss) of 341, 395, and 398 °C, and high glass-transition temperatures (Tg) of 83, 126, and 132 °C are recorded for DMFBP-PXZ, DPF-BP-PXZ, and SBF-BP-PXZ, respectively (Figure S1, Supporting Information), which are conducive to fabricating stable EL devices. Based on the onset of oxidation and reduction potentials relative to Fc/Fc+, the highest occupied molecular orbital (HOMO) energy levels are estimated to be −5.01 eV for DMF-BP-PXZ, −5.02 eV for DPFBP-PXZ, and −5.04 eV for SBF-BP-PXZ, respectively. The lowest unoccupied molecular orbitals (LUMO) energy levels of DMFBP-PXZ, DPF-BP-PXZ, and SBF-BP-PXZ are −2.83, −2.84, and −2.88 eV, respectively
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