Exact solution of kinetic analysis for thermally activated delayed fluorescence materials

The photophysical analysis of thermally activated delayed fluorescence (TADF) materials has become instrumental to providing insight into their stability and performance, which is not only relevant for organic light-emitting diodes (OLED), but also for other applications such as sensing, imaging and photocatalysis. Thus, a deeper understanding of the photophysics underpinning the TADF mechanism is required to push materials design further. Previously reported analyses in the literature of the kinetics of the various processes occurring in a TADF material rely on several a priori assumptions to estimate the rate constants for forward and reverse intersystem crossing (ISC and RISC, respectively). In this report, we demonstrate a method to determine these rate constants using a three-state model together with a steady-state approximation and, importantly, no additional assumptions. Further, we derive the exact rate equations, greatly facilitating a comparison of the TADF properties of structurally diverse emitters and providing a comprehensive understanding of the photophysics of these systems.