Alkylene Spacer Engineering for Boosting Circularly Polarized Luminescence in Homopolypeptide Self-Assembly

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Abstract
Functional materials with circularly polarized luminescence (CPL) property featuring both high luminescence efficiency and strong chiroptical activity are highly desirable for advanced photonic applications such as three-dimensional displays, optical encryption, asymmetric photochemistry, and biomedical imaging, yet remain challenging to develop. While extensive efforts have focused on engineering chromophore structures and chiral building blocks, the influence of the spacer connecting luminophores and chiral scaffolds on CPL generation remains poorly understood. Herein, we report an alkylene spacer engineering strategy to regulate supramolecular chirality and CPL performance in homopolypeptide-based assemblies. A series of luminescent homopolypeptides were synthesized, bearing an achiral terminal luminophore connected to the backbone through alkylene spacers of varying lengths. By self-assembly, nanotoroid-dispersed aqueous solutions were obtained from these homopolypeptides with photoluminescence quantum yields exceeding 50%. Despite their nearly identical morphologies, the assemblies exhibited markedly different CPL activities. Increasing the spacer length led to continuous enhancement of CPL performance, with the luminescence dissymmetry factor (glum) increasing by an order of magnitude from 1.1 × 10–3 to 1.1 × 10–2. Structural characterization and molecular simulations reveal that spacer elongation strengthens the coupling between the terminal luminophore and helical polypeptide scaffold, facilitating more efficient chirality transfer and supramolecular chirality amplification within the toroidal assemblies. Further optimizing the degree of polymerization promotes supramolecular ordering and amplifies CPL activity, yielding an enhanced glum up to 1. 8 × 10–2. This work reveals a previously overlooked role of spacer-mediated chirality communication between the terminal luminophore and helical polypeptide scaffolds and establishes alkylene spacer length as a critical structural parameter for chirality amplification in this supramolecular CPL system, providing new insights into the “molecular structure – supramolecular assembly – chiroptical property” relationship.
Funding Information
  • Shanghai Municipal Education Commission (2023ZKZD28)
  • Science and Technology Commission of Shanghai Municipality (25JD1401000)
  • Fundamental Research Funds for the Central Universities
  • National Natural Science Foundation of China (NSFC) (22301152)
  • National Natural Science Foundation of China (NSFC) (22335005)
  • National Natural Science Foundation of China (NSFC) (22573087)

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