Heavy atom-free triplet photosensitizer based on thermally activated delayed fluorescence material for NIR-to-blue triplet-triplet annihilation upconversion

Triplet-triplet annihilation(TTA) upconversion-based materials have potential application in the broad range of research areas, including photocatalysis and life sciences. However, near-infrared(NIR)-to-blue upconverted emission is preferred for most of the practical applications, but developing a NIR-to-blue TTA upconversion system is a challenging task in photochemistry. In this work, a thermally activated delayed fluorescence(TADF) material with intense visible-to-NIR absorption is demonstrated that shows a longer triplet state lifetime(32 μs) and high triplet state energy(E_(T)= 1.55 e V). For the first time, a heavy atomfree NIR(λ_(ex)> 650 nm) to blue(λ_(em)< 460 nm) TTA upconversion system was devised, employing the dimeric borondifluoride curcuminoid TADF material as triplet photosensitizer(PS) and a large anti-Stokes shift(0.88 e V) along with moderate upconversion yield was achieved. Our work provides the solution and guidance for the future development of purely organic heavy atom-free NIR activating TTA upconversion system for a wide array of applications.