Self-doping mechanism for thermally activated delayed fluorescence molecules: a theoretical perspective

Interesting properties of dual conformations of thermally activated delayed fluorescence molecules show various novel applications in self-doping systems. However, the species and quantities of self-doping systems are not enough to satisfy the requirements and a theoretical investigation to reveal the self-doping mechanism is highly desired. By analysing the potential energy surface, two stable conformations of TP2P-PXZ-qa (QA) and TP2P-PXZ-qe (QE) are determined. The basic geometric and electronic structures are optimised, frontier orbital distributions and energies are obtained, transition properties are analysed and the energy consumption processes of excited states are analysed. Results indicate that two conformations (QA and QE) coexist in the solid phase, the QA conformation acts as host and the QE conformation acts as guest. Efficient intersystem crossing (ISC) and reverse ISC processes are determined for QE conformation. In addition, a substantial overlap exists between the emission spectrum of the QA conformation and the absorption spectrum of the QE conformation, indicating an effective energy transfer process from host to guest. Thus, relationships between molecular structures and photophysical properties are illustrated and a self-doping mechanism is theoretically revealed. Our work rationalises the experimental observations and offers a theoretical perspective for the self-doping mechanism, contributing to the development of efficient non-doped emitters. {GRAPHICAL ABSTRACT}