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Hall, David ; Rajamalli, Pachaiyappan ; Duda, Eimantas ; Suresh, Subeesh Madayanad ; Rodella, Francesco ; Bagnich, Sergey ; Carpenter-Warren, Cameron L. ; Cordes, David B. ; Slawin, Alexandra M. Z. ; Strohriegl, Peter ; Beljonne, David ; Köhler, Anna ; Olivier, Yoann ; Zysman-Colman, Eli:
Substitution Effects on a New Pyridylbenzimidazole Acceptor for Thermally Activated Delayed Fluorescence and Their Use in Organic Light-Emitting Diodes.
In: Advanced Optical Materials.
Bd. 9
(2021)
Heft 20
.
- 2100846.
ISSN 2195-1071
DOI: https://doi.org/10.1002/adom.202100846
Abstract
In this work a new acceptor is used for use in thermally activated delayed fluorescence (TADF) emitters, pyridylbenzimidazole, which when coupled with phenoxazine allows efficient TADF to occur. N-functionalization of the benzimidazole using methyl, phenyl, and tert-butyl groups permits color tuning and suppression of aggregation-caused quenching (ACQ) with minimal impact on the TADF efficiency. The functionalized derivatives support a higher doping of 7 wt% before a fall-off in photoluminescence quantum yields is observed, in contrast with the parent compound, which undergoes ACQ at doping concentrations greater than 1 wt%. Complex conformational dynamics, reflected in the time-resolved decay profile, is found. The singlet−triplet energy gap, ΔEST, is modulated by N-substituents of the benzimidazole and ranges of between 0.22 and 0.32 eV in doped films. Vacuum-deposited organic light-emitting diodes, prepared using three of the four analogs, show maximum external quantum efficiencies, EQEmax, of 23.9%, 22.2%, and 18.6% for BIm(Me)PyPXZ, BIm(Ph)PyPXZ, and BImPyPXZ, respectively, with a correlated and modest efficiency roll-off at 100 cd m–2 of 19% 13%, and 24% of the EQEmax, respectively.