Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 123, Issue 49, Pages 29875-29883Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.9b08563
Keywords
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Funding
- National Key R&D Program of China [2016YFB0401004]
- National Natural Science Foundation of China [51873183, 51673164]
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Highly efficient organic light-emitting diodes (OLEDs) employing metal-free thermally activated delayed fluorescence (TADF) emitters have attracted much attention in recent years. Efficient TADF mainly occurs in charge-transfer (CT) molecules. Here, we demonstrate that a small dipole moment for TADF emitters in the S-1 state is key for device stability by comparing two green TADF emitters with the same moieties but different types of linker. The compound 1AC-TRZ with a 9,9-dimethyl-9,10-dihydroacridine donor and a triphenyltriazine acceptor attached at the 1- and N-positions of carbazole has a smaller excited-state dipole moment (11 D) than the 3- and N-substituted analog 3AC-TRZ (30 D). Although the emission spectra and efficiencies of their devices are similar, the operational lifetime of the 1AC-TRZ-based device is much longer than that of the 3AC-TRZ-based device. Time-resolved emission spectra indicate that the S-1 energy of 3AC-TRZ in doped films is higher than that of 1AC-TRZ at the start of nanosecond solvation experiment suggests that the short-term existence (<1 ns) of high energy (>2.9 eV) excitons induced degradation in films. Our study reveals a relationship between solid-state solvation and new guideline for designing stable green and blue TADF emitters.
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