Molecular engineering of organic room temperature phosphorescence emitters for next generation applications

The emergence of room-temperature phosphorescence (RTP) has opened a new era in material science, offering metal-free alternatives for efficient triplet exciton utilization. Key advances, such as the incorporation of non-metallic heavy atoms (S, Se, B), rigid conjugated scaffolds, and intramolecular locking strategies, have enabled efficient inter-system crossing (ISC), spin-orbit coupling (SOC), and the stabilization of triplet states, leading to efficient RTP. Alongside RTP, thermally activated delayed fluorescence (TADF) emitters have emerged as another breakthrough in purely organic triplet harvesting. Both classes of materials share design synergies, such as rigid polycyclic frameworks and precise electronic control, yet differ fundamentally in their excited-state dynamics: RTP relies on triplet phosphorescence, while TADF relies on reverse inter-system crossing. Interestingly, recent studies reveal that certain TADF molecules can also exhibit RTP, owing to their structural modulation. This duality suggests exciting opportunities to design multifunctional emitters that selectively access TADF and RTP, thereby broadening the application landscape. This review critically surveys and classifies the state-of-the-art in organic RTP molecules showing TADF, outlining molecular design strategies, photo physical principles and their potential applications in OLEDs, bio imaging, information encryption, X-Ray imaging, time-gated bioassay, photodynamic therapy, flexible wearable optoelectronic devices and circularly polarized room-temperature phosphorescence. Finally, the challenges and opportunities are identified for expanding these classes of organic triplet-harvesting molecules.