Multiple resonance thermally activated delayed fluorescence enhanced by halogen atoms

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2022-08, Vol.1 (33), p.11855-11861
• Main Authors: Lee, Youngnam, Hong, Jong-In
• Format: Article
• Language: English
• Subjects: Emitters; Fluorescence; Photoluminescence; Quantum efficiency; Rate constants; Resonance
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d2tc02909j

We synthesized halogen-substituted multiple-resonance (MR) thermally activated delayed fluorescence emitters, namely 2,12-dichloro- N , N ,5,9-tetrakis(4-chlorophenyl)-5,9-dihydro-5,9-diaza-13 b -boranaphtho[3,2,1- de ]anthracen-7-amine (Cl-MR) and 2,12-dibromo- N , N ,5,9-tetrakis(4-bromophenyl)-5,9-dihydro-5,9-diaza-13 b -boranaphtho[3,2,1- de ]anthracen-7-amine (Br-MR). Cl-MR and Br-MR exhibited a decreased delayed fluorescence lifetime and an enhanced reverse intersystem crossing rate without any changes in Δ E ST and orbital distribution compared with a non-halogenated MR emitter. Cl-MR exhibited a high photoluminescence quantum yield (PLQY) of 85% and external quantum efficiency (EQE) of 17%; however, Br-MR did not exhibit any enhancement in the PLQY and EQE. The different performances of Cl-MR and Br-MR were rationalized by analysing the rate constants of the excited states and bond dissociation energies of the carbon-halogen bonds. Halogenated multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters, Cl-MR and Br-MR, were developed to improve the reverse intersystem crossing rate constant of MR-TADF emitters.