Steering Nanohelix and Upconverted Circularly Polarized Luminescence by Using Completely Achiral Components

Abstract

Enormous attention has been paid to upconverted circularly polarized luminescence (UC-CPL). However, so far, chiral species are still needed in UC-CPL materials, either through the covalent or noncovalent bond. Here, we report a general supramolecular coassembly approach for the fabrication of UC-CPL systems from completely achiral components. We have found that an achiral C 3 -symmetric molecule could form a chiral nanohelix through symmetry breaking, which could serve as a general helical platform to endow achiral guests with induced chirality and CPL activity. Two different photon upconversion systems, namely, triplet−triplet annihilation photon upconversion (TTA-UC) donor/acceptor pairs and inorganic lanthanide upconversion nanoparticles (UCNPs), are selected. When these two systems coassembled with the chiral nanohelix made from an achiral C 3 -symmetric molecule, hybrid nanohelix structures formed and UC-CPL activity was induced. Through such an approach, we demonstrated that the fabrication of the UC-CPL materials does not require any chiral molecules. Moreover, we have shown that the polarization of UC-CPL can be tuned by the helicity of the nanohelix, which could be controlled through the seeded vortex. Our work provides a general approach for designing tunable UC-CPL materials from completely achiral motifs, which largely expands the research scope of the CPL materials.

Frontiers in circularly polarized luminescence: molecular design, self-assembly, nanomaterials, and applications

“…The efficiency of the TTA process will be reduced due to chiralityinduced spin polarization, which is possibly responsible for the enhancement of g lum value. Moreover, CPLs based on TTA mechanism have been widely presented in other systems like liquid crystals [278,279] and supramolecular gels [280,281]. These chiral hosts have received considerable attentions for the flexible controllability of CPL.…”

“…These chiral hosts have received considerable attentions for the flexible controllability of CPL. Recent work has revealed a strategy by using achiral C 3 -symmetric molecules to build the chiral nanohelix through symmetry breaking, and then it can load TTA-UC donor/acceptor pairs [280]. Seeded vortex is proven available to control the chirality of assembly and corresponding UC-CPL.…”

“…Its ultraviolet region has been successfully used for the enantioselective polymerization of diacetylene. In addition, the approach of seeded vortex could be used to adjust chiral assembly, thus UCNPs were successfully blended into the nanohelix, enabling the UC-CPL emission [280]. Other chiral environments were also demonstrated like liquid crystal [282][283][284] and metal-organic framework [285,286], which built powerful platforms for constructing stimulus responsiveness of UC-CPL.…”

Hierarchical self-assembly into chiral nanostructures

“…14 In addition, chiral supramolecular structures are considered as excellent matrix and templates to regulate the assembly of inorganic building blocks, 221 endowing hybrid assemblies with compelling chiroptic performances, such as chiral plasmonic and circularly polarized emission. 2,15,190,192,[222][223][224] Therefore, utilizing the hierarchical self-assembly strategy to combine chiral molecules and other functional materials is a promising research direction as the chirality might endow the hybrid assemblies with interesting and exciting properties.…”

Shining light on chiral inorganic nanomaterials for biological issues

“…For this matter, applications of CPL properties on biological issues are seriously limited by low tissue penetration depth and phototoxicity to healthy tissues. It is then promising that with development of CPL testing techniques to NIR region or new species of CPL-active nanomaterials with NIR emissions or upconverted properties 197 , lanthanide UCNPs for instance, there would be plenty of room available for more CPL-based bioinspired applications in future.…”