Cucurbituril-Mediated Conformational Control: From Molecular Manipulation to Functional Applications

High Resolution Image Download MS PowerPoint Slide Conspectus Molecular conformation is a fundamental determinant of intramolecular interactions, reactivity, and conjugation extent in organic molecules, directly influencing properties ranging from photophysical characteristics to chemical reactivity. Consequently, precise control over molecular conformation represents both a significant challenge and opportunity in organic chemistry and materials science, enabling the rational design of functional materials. Beyond covalent modifications such as steric group incorporation, molecular conformation can also be effectively regulated through noncovalent host–guest complexation in supramolecular chemistry. Among the various supramolecular tools available, the cucurbit[ n ]uril (CB[ n ], n = 5–8, 10) family of synthetic macrocycles has emerged as a powerful tool for conformational manipulation. CB[ n ] hosts feature rigid, hydrophobic cavities and electronegative carbonyl portals, providing excellent binding affinity and selectivity toward cationic guest molecules through a combination of hydrophobic effects, ion–dipole interactions, and hydrogen bonding. Larger homologues such as CB[7], CB[8], and CB[10] possess cavities capable of encapsulating and precisely manipulating molecular conformations through host–guest interactions, thereby profoundly altering guest properties. The evolution of CB[ n ] hosts from simple molecular containers to conformational regulators has enabled the construction of diverse functional supramolecular materials. Recently, numerous supramolecular assemblies have been developed through CB[ n ]-mediated conformational control. This Account provides an overview of recent fundamental advances and applications in CB[ n ]-mediated conformational control, establishing clear structure–property relationships between conformation manipulation and material functionality. We categorize CB[ n ]-mediated conformationally adaptive guest molecules into five representative paradigms, each demonstrating a distinct mode of conformational modulation: the induced U-shaped folding of flexible alkyl chains within the hydrophobic cavity, the folded conformation of charge-transfer complexes within CB[ n ], controllable photoresponsiveness of diarylethene molecular photoswitches, controlled twisting of sterically constrained molecules, and linear donor–acceptor type molecules. Through a careful evaluation of selected examples, we demonstrate that CB[ n ] functions as a conformational regulator rather than merely a molecular container with the confined microenvironment effectively shifting the conformation into normally disfavored states. More importantly, this complexation process yields host–guest systems with unique properties markedly different from the free guest molecules, including tunable fluorescence or room temperature phosphorescence (RTP) emission as well as different responsive behaviors toward light and external mechanical stimulation. We further explore the applications of CB[ n ]-mediated conformational control, including tunable luminescent materials for sensing and information encryption, efficient RTP materials for bioimaging, photochromic materials, mechanochromic materials, and stimuli-responsive biomaterials. Finally, this Account outlines the challenges and future perspectives for designing CB[ n ]-based systems with multiple functions. By integrating molecular design with diverse applications across chemistry, materials science, and bioimaging, this Account aims to deepen the understanding of supramolecular conformational engineering while inspiring broader efforts to translate CB[ n ]-mediated conformational control into advanced material functionalities.