Understanding the origin of thermally activated delayed fluorescence in coplanar emitters Katrina Bergmann and Zachary M. Hudson The University of British Columbia, Canada
Materials that exhibit thermally activated delayed fluorescence (TADF) are important for applications in organic light-emitting diodes, light-emitting electrochemical cells, time-resolved fluorescence bioimaging, and photocatalysis. To improve the design of TADF emitters and accelerate conversion of triplet excitons to singlets, two principal techniques have been identified: (1) utilizing the heavy atom effect to increase spin orbit coupling, or (2) spatially separating the frontier molecular orbitals through orthogonal donor-acceptor design to minimize the singlet-triplet energy gap (∆E ST ). Planarized donor-acceptor materials exhibiting TADF have recently attracted attention due to their advantageous properties such as high colour purity, improved photostability, and high quantum yields, 1 but with large ∆E ST values and no heavy atoms, the origin of their TADF properties remains unclear. Our recent work on a pair of planar isomers that do and do not display TADF highlights the importance of modeling excited state potential energy surfaces of coplanar emitters to rationalize their photophysical behaviour. 2 However, a broader understanding of TADF in planar emitters is still missing. Herein, we investigate two sets of previously reported planar fluorophores: one set that exhibits TADF, and one set that does not. This theoretical investigation reveals trends that discernibly separate a variety of TADF emitters from non-TADF emitters, providing concrete metrics from which future planar emitters can be designed. References 1. I. Zoh, M. Imai-Imada, J. Bae, H. Imada, Y. Tsuchiya, C. Adachi and Y. Kim, J. Phys. Chem. Lett., 2021, 12 , 7512-7518. 2. K. Bergmann, R. Hojo and Z. M. Hudson, J. Phys. Chem. Lett., 2023, 14 , 310-317.
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© The Author(s), 2023
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