Chirality-Induced Exciton Spin Selectivity in Triplet Fusion Photon Upconversion.

Chirality-induced spin selectivity (CISS) has been extensively studied in the transport of spin-polarized charge carriers, yet its role in the generation of spin/triplet excitons remains largely unexplored. Here, spin dynamics simulations combined with magnetophotoluminescence measurements demonstrate that CISS strongly influences the formation of triplet-triplet (TT) pairs during triplet fusion photon upconversion in extremely dilute solutions (10-6 mol L-1), with the racemic system exhibiting stronger upconversion emission than its enantiopure counterparts. Because the photophysical properties of chiral and racemic systems are otherwise identical, this difference is attributed to chirality-induced exciton spin selectivity (CIESS), which leads to imbalanced populations on the sublevels of TT pairs in chiral annihilators. Distinct "U-shaped" and "W-shaped" magnetophotoluminescence responses, observed in chiral and racemic systems, respectively, further indicate that spin-polarized triplet excitons are preferentially generated in chiral systems and form high-spin TT pairs. These findings provide compelling theoretical and experimental evidence for the CIESS effect of excitons.