Evolution of color-tunable TADF emitters in OLEDs: from design strategies to color modulation

Abstract

Organic thermally activated delayed fluorescence (TADF) materials have gained considerable attention in recent times, specifically in advancing organic light-emitting diodes (OLEDs) due to the possibility of achieving 100% EQE and the ability to tune their emission color. This review highlights the evolution of molecular design strategies that enable precise control of the singlet–triplet energy gap (ΔE_ST) and reverse intersystem crossing (RISC), thereby advancing device efficiency and color purity. We discuss the progression from early donor–acceptor systems to more advanced methodologies, including π-conjugation tuning and steric and substituent engineering, through-space charge transfer (TSCT), multi-resonance (MR) TADF, and circularly polarized luminescence (CPL)-active TADF emitters. In the later sections, we summarize the progression from the early conceptual development to the recent emergence of blue, green, red, and white TADF OLEDs and their operation mechanism. Thus, the objective of this review is to connect molecular design strategies with the development of next-generation TADF materials for high-performance, color-tunable OLEDs.