Molecular Locking in Triplet Sensitization Amplifies Circularly Polarized Luminescence

The potential of chiral organic molecules exhibiting circularly polarized luminescence (CPL) for practical applications hinges on the luminescence efficiency and dissymmetry factor (g_lum). However, surpassing the molecular limitations of dissymmetry factors remains a significant challenge, primarily due to the different parity selection rules governing the electric and magnetic dipole moments in chiral molecules. In this study, we tackle this inherent constraint by designing a triplet sensitization photon upconversion system using nontoxic CuInS₂ quantum dots (QDs) photosensitizer. We demonstrate a 43-fold amplification of CPL in QD-sensitized triplet fusion process compared to the direct photoexcitation. Notably, a high green-to-blue upconversion quantum efficiency of 12.7 ± 0.19% (normalized to 100%) was achieved. The dissymmetry factors of QD-sensitized upconversion CPL outperform previous reports based on molecular photosensitizers. The observed large g_lum, according to our modeling and first-principles calculations, originates from the unique structural rearrangement of the chiral emitter during the ultrafast triplet energy transfer process. Our work provides a new strategy and mechanistic insights for CPL amplification through triplet sensitization.