Triplet-Triplet Annihilation Upconversion Circularly Polarized Luminescence That Originates from Achiral and Racemic Luminophores Encapsulated in Chiral Silica

Circularly polarized luminescence (CPL) has emerged as a key optical property with chiral-photonic and optoelectronic applications. However, conventional CPL systems rely on synthetically demanding chiral luminophores that emit at fixed wavelengths, which limits tunability and efficiency. In this study, we demonstrate that achiral or racemic luminophores co-encapsulated with photosensitizers in the helical nanocavities of chiral silica exhibit upconversion CPL (UC-CPL). The chiral silica, which is derived from polymethylvinylsiloxane comprising polyhedral oligomeric silsesquioxane decorated with enantiomeric N-(tert-butoxycarbonyl)cysteine methyl ester moieties (PMVS-POSS-Cys), has a helical structure with a preferred-handedness that facilitates efficient triplet-triplet energy transfer (TTET) and triplet-triplet annihilation (TTA). The resulting materials exhibit distinct CPL and UC-CPL signals when excited at 365 and 532 nm, respectively, despite the achiral nature of the luminophore. This study unprecedentedly demonstrates UC-CPL from achiral emitters within chiral silica matrices, which is achieved through chiral induction in the solid-state helical silica frameworks. The strategy described herein provides a general and versatile platform for developing energy-efficient, wavelength-tunable chiral-photonic materials without the need for elaborate chiral syntheses.