Triggering the Vapochromic Behavior in C₆₀ via the Supramolecular Wrapping of st-PMMA

Understanding the physicochemical modulation of functional molecules is the primary step in exploring novel stimuli-responsive materials, and preventing the π-π stacking configuration of π-conjugated molecules has been an effective strategy of vapochromic material development, such as of nanoporous frameworks. Nevertheless, the more complicated synthetic strategy should in fact be applied in many circumstances. In this study, we explore a facile supramolecular strategy where the commodity plastic, syndiotactic-poly(methyl methacrylate) (st-PMMA), is utilized to wrap C₆₀ to form the inclusion complex. The structural characterization revealed that C₆₀s in the st-PMMA supramolecular helix had a lower coordination number (CN = 2) compared to the face-centered-cubic packing of pure C₆₀s (CN = 12). Since the st-PMMA/C₆₀ helical complex has structural flexibility, the π-π stacking structure of C₆₀ was further interrupted by the intercalation of toluene vapors, and the complete isolation of C₆₀ in the complex induced the desired vapochromic behavior. Furthermore, the aromatic interaction between C₆₀ and aromatic solvent vapors enabled the st-PMMA/C₆₀ inclusion complex to selectively encapsulate chlorobenzene, toluene, etc., and induce the color change. The st-PMMA/C₆₀ inclusion complex exhibited a transparent film of sufficient structural integrity such that it can still induce a reversible color change after several cycles. As a result, a new strategy has been discovered for the development of novel vapochromic materials via host-guest chemistry.