Bigger Molecules Enter Smaller Channels of Zeolites via Inward-Coil-Alike Adaptation

Despite the well-defined pore apertures of zeolites, accumulating evidence reveals that molecules exceeding the nominal dimensions may permeate the pore, challenging the classical paradigm of size-exclusion molecular sieving. Although the framework flexibility of zeolites accommodating guest molecules has been reported, the potential structural adaptation of guest molecules remains underexplored. In this study, we demonstrated that a bulky fluorophore with a minimum projection diameter exceeding the zeolite pore size by ∼2-fold can undergo inward coiling, reducing size by about 18-27%, and enabling entry into the subnanometric channels of various zeolite frameworks, as confirmed by time-resolved fluorescence techniques, X-ray diffraction refinement, and in situ electron microscopy. These findings suggest, for the first time, that beyond the intrinsic flexibility of zeolite frameworks, guest molecules themselves may exhibit an unexpectedly high degree of conformational alternation to facilitate pore entry. Additionally, we demonstrated photophysical alternation of fluorophores as a result of energy state change in response to structure adaptation to various zeolites. Consequently, the fluorescence lifetime serves as a sensitive descriptor of molecular strain, providing a readout of the diverse confined microenvironments within zeolites. This approach establishes a novel strategy for probing pore accessibility and host-guest interactions in microporous materials.