Triplet-to-singlet FRET (TS-FRET) in pure organic phosphors: emerging applications and new opportunities.

Förster resonance energy transfer (FRET) involving spin conversion from the triplet to the singlet state, commonly referred to as triplet-to-singlet FRET (TS-FRET) or phosphorescence energy transfer, has recently emerged as an active area of research in purely organic systems, driven by the development of efficient organic phosphors. This mechanism enables delayed fluorescence with several advantages, including long-lived emission, high quantum yields, large Stokes shifts, and tunable emission profiles, all achieved without the need for complex molecular design strategies. While the growing number of TS-FRET scaffolds has expanded the chemical space of such systems, further progress in this field depends on redirecting the focus toward their practical applications and long-term potential, akin to the well-established singlet-to-singlet FRET systems. With this in mind, this perspective aims to provide a functional and forward-looking interpretation of TS-FRET systems. Alongside a concise overview of their historical development and underlying principles, it highlights key application areas where TS-FRET can make impactful contributions, thereby charting a course for advancing the field beyond current paradigms.