Substitution effects on a new pyridylbenzimidazole acceptor for thermally activated delayed fluorescence and their use in organic light-emitting diodes

David Hall, Pachaiyappan Rajamalli, Eimantas Duda, Subeesh Madayanad Suresh, Francesco Rodella, Sergey Bagnich, Cameron Lewis Carpenter-Warren, David Bradford Cordes, Alexandra Martha Zoya Slawin, Peter Strohriegl, David Beljonne, Anna Köhler, Yoann Olivier, Eli Zysman-Colman

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6 Citations (Scopus)
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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.
Original languageEnglish
Article number2100846
Number of pages13
JournalAdvanced Optical Materials
Volume9
Issue number20
Early online date2 Aug 2021
DOIs
Publication statusPublished - 18 Oct 2021

Keywords

  • DFT calculation
  • Organic light-emitting diodes
  • Photophysics
  • Pryidylbenzimidazole
  • Thermally activated delayed fluorescence

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