Structural and Electronic Properties of the NAI-DMAC Organic Emitting Diode: A Thermally Activated Delayed Fluorescence Compound*

Thermally activated delayed fluorescence compounds (TADFs) are a class of purely organic light emitting diodes^[1] based on reverse intersystem crossing processes. Despite the successful synthesis of blue/green TADF compounds, the search for efficient orange-red fluorescent TADFs remains an open problem. NAI-DMAC^[2] [C₃₇H₃₂N₂O₂] is one of the few orange-red light emitters with an external quantum efficiency of ~ 30%. Here we present a first principle study of NAI-DMAC both in the dilute and solid state limit. We carried out First-Principles Molecular Dynamics simulations with the Qbox code (http://qboxcode.org) at different temperatures and computed ground to excited state transitions by employing range-separated hybrid functionals^[3], as well as the SCAN functional^[4]. We present results for the energy difference between singlet and triplet excited states (ΔE_ST), and we discuss how ΔE_ST is related to structural differences in the ground and excited states, in particular to the dihedral angle between the donor and acceptor moieties.

[1] H. Uoyama, et al. Nature, (2012), 492, 234-238;
[2] W. Zeng, et al. Adv. Mat., (2018), 30(5), 1704961;
[3] J. H. Skone, et al. Phys. Rev. B 93.23 (2016): 235106;
[4] J. Sun, et al. Phys. Rev. Lett. 115.3 (2015): 036402.