First-Principles Investigation of Thermally Activated Delayed Fluorescence Processes*

Thermally Activated Delayed Fluorescence (TADF) compounds are promising materials for the realization of next generation Organic Light Emitting Diodes ^[1]. Among several TADF systems recently proposed in the literature, NAI-DMAC^[2][C₃₇H₃₂N₂O₂] represents one of the few available orange-red emitters, with a remarkable 30% external quantum efficiency. We present a detailed first principle study of the NAI-DMAC compound, and we consider both the single molecule (dilute limit) and the crystal (high-packing limit). We carried out First-Principles Molecular Dynamics simulations at finite temperature with the Qbox^[3] code (http://qboxcode.org) and we analyzed the structural motifs that lead to the desired energy splitting between the singlet and triplet excited states. This splitting is the key driving force of the TADF process. We also computed diabatic coupling parameters associated to the charge mobility^[4] and we discuss how charge transfer processes occur in NAI-DMAC.

[1] H. Uoyama, et al., Nature, 2012, 492, 234-238;
[2] W. Zeng, et al., Adv. Mat., 2018, 30(5), 1704961;
[3] F. Gygi, IBM J. Res. Dev., 2008, 52, p.137;
[4] H. Ma, et. al., J. Comp. Chem., 2020, 41: 1859-1867.