Upconverting and downshifting circularly polarized luminescence in a superstructural helix

The modulation of circularly polarized luminescence (CPL) has become an increasingly prominent area of research. In this study, we propose a unique “one-excitation-to-three-emissions” CPL system through the co-assembly of an upconversion system, incorporating one sensitizer (Pt(II) mesotetraphenyl tetrabenzoporphyrine, PtTPBP) and two annihilators (R/S-DPA and R/S-BDP) within liquid crystals. The chiral nature of the annihilators induces a transformation of the nematic liquid crystal into chiral nematic liquid crystals (N*LC), establishing an excellent chiral matrix. Upon the incorporation of the sensitizer PtTPBP and subsequent excitation at 635 nm, the system demonstrates two independent triplet-triplet annihilation photon upconversion (TTA-UC) with the emission in blue and yellow, aided by thermally activated triplet-triplet energy transfer (TTET). This is accompanied by the simultaneous generation of upconverting circularly polarized luminescence (UC-CPL) and downshifting near-infrared circularly polarized luminescence (DS-CPL) originating from the residual luminescence of PtTPBP. Remarkably, fine-tuning the ratio between the two annihilators allows the TTA-UC system to exhibit multicolor CPL emission with an amplified luminescence dissymmetry factor (g_lum, reaching up to 0.6). Our study unveils a previously unreported “one-excitation-to-three-emissions” system and provides a versatile strategy for modulating CPL emissions, surpassing conventional methodologies.