Chiral Display of Pyrenes on a Peptoid Backbone: Conformational Homogeneity of Peptoid Controls Excimer Chirality

Controlling chromophore chirality in three-dimensional space is crucial for understanding the structure-chiroptical relationship. Such control enables the prediction of ideal materials for use in chiral photonic applications. In this study, optically active multipyrene systems are synthesized on peptoids. Pyrene-based chiral submonomers, (S)- and (R)-1-pyrenylethylamine (s1pye and r1pye), are successfully incorporated into peptoids as the respective (S)- and (R)-N-(1-pyrenylethyl)glycine (Ns1pye and Nr1pye) units. NMR spectroscopy revealed length- and N-acetylation-dependent conformational homogeneity enhancement in solution, stabilizing cis-amides in Ns1pye-containing peptoids. The X-ray crystal structure of Ns1pye tetramer displayed a polyproline type-I (PPI)-like helix. All of the pyrene-related absorptions are circular dichroism (CD) active, and the CD signal related to the long-axis-polarized transition increased with helical stabilization. Intramolecular excimer generation yielded significant circularly polarized luminescence (CPL) in the excimer emission region. Early-stage peptoids emitted left-handed CPL, but upon acquiring a PPI-like helix character, CPL handedness became inverted. The CPL dissymmetry factor (glum) was comparable or superior (10-2) to that of chiral organic dyes (10-5-10-2). This new class of helical pyrene-containing peptoids provides a CPL-active intramolecular excimer, modulating optical activity through peptoid secondary structure homogeneity. Peptoids generating circularly polarized luminescence (CPL) are synthesized and characterized for the first time. Structural determination employed nuclear magnetic resonance spectroscopy and X-ray crystallography. The peptoid scaffold facilitated chirality transfer to the resulting intramolecular pyrene excimer, demonstrating notable CPL activity (glum approximate to 10-2). The role of conformational homogeneity in modulating CPL activity and handedness is presented.image (c) 2023 WILEY-VCH GmbH

Automated summary

Controlling the chirality of chromophores in three-dimensional space is important for understanding the relationship between structure and chiroptical properties. In this study, the authors synthesized optically active multipyrene systems on peptoids, demonstrating the control of optical activity through peptoid secondary structure homogeneity. The resulting peptoids exhibited circularly polarized luminescence (CPL) through intramolecular excimer generation. The study highlights the role of conformational homogeneity in modulating CPL activity and handedness.