Theoretical insights into molecular design of hot-exciton based thermally activated delayed fluorescence molecules

Abstract

Despite the recent breakthroughs in the TADF process, more research is needed to understand its mechanism and develop rational molecular designs for structures with higher efficiencies and quantum yield. Hot exciton-based TADF materials, like traditional (cold) TADF, can effectively utilize singlet and triplet excitons, theoretically resulting in 100% IQE. However, in contrast to cold TADF (from low-lying T₁ to S₁), the RISC process in hot TADF occurs from high-lying triplet to singlet excited states (from T_m(m > 1) to S_n(n > 1)). However, designing materials that satisfy conditions for hot exciton formation, such as large triplet spacing in lower states and a small singlet-triplet gap in higher states, remains a difficult job. In this study, we explore and analyze the fundamental concepts of molecular design and suggest a design strategy by establishing structure-property relationships for hot-TADF molecules using density functional theory methods. This study could lead to new insights into molecular design approaches for organic materials with many hot exciton channels, which could lead to better exciton utilization.