γ-Cyclodextrin-Based 2:2 Host-Guest Complexes With Emergent Circularly Polarized Luminescence

Abstract

Discrete 2:2 host-guest complexes provide a well-defined platform for correlating supramolecular structure with emergent photophysical behavior. Although γ-cyclodextrin (γ-CD) is widely used in aqueous host-guest chemistry, structurally well-defined 2:2 complexes and their formation mechanisms remain poorly understood. Here we report a γ-CD-mediated 2:2 host-guest complex formed with 1,3,6,8-tetrakis(4-carboxyphenyl)pyrene tetrasodium salt (TCP) and systematically elucidate its structural, mechanistic, and photophysical characteristics. Combined ¹H NMR, 2D NMR, and DOSY analyses resolve the 2:2 architecture, while thermodynamic and kinetic studies reveal a multistep complexation network involving 1:1, 1:2, and 2:2 species, with dimerization providing the dominant thermodynamic driving force. The resulting 2:2 complex exhibits enhanced fluorescence emission and pronounced chiroptical responses, including circular dichroism and circularly polarized luminescence, arising from supramolecular chirality induced by the chiral γ-CD cavities. Importantly, analogous γ-CD-mediated 2:2 complexation and associated photophysical features are also observed for a tetraphenylethylene-based guest, indicating that this binding mode is not limited to a single chromophoric scaffold. This study clarifies how 2:2 host-guest complexes can form in γ-CD systems and provides mechanistic insight into the emergence of chiral photophysical properties in such complexes.

Keywords

γ-cyclodextrin / 2:2 complexes / circularly polarized luminescence / host-guest

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