Switching molecular recognition selectivities by temperature in a diffusion-regulatory porous material

Abstract Over the long history of evolution, nature has developed a variety of biological systems with switchable recognition functions, such as the ion transmissibility of biological membranes, which can switch their ion selectivities in response to diverse stimuli. However, developing a method in an artificial host-guest system for switchable recognition of specific guests upon the change of external stimuli is a fundamental challenge in chemistry because the order in the host-guest affinity of a given system hardly varies along with environmental conditions. Herein, we report temperature-responsive recognition of two similar gaseous guests, CO2 and C2H2, with selectivities switched by temperature change by a diffusion-regulatory mechanism, which is realized by a dynamic porous crystal featuring ultrasmall pore apertures with flip-flop locally-motive organic moiety. The dynamic local motion regulates the diffusion process of CO2 and C2H2 and amplifies their rate differences, allowing the crystal to selectively adsorb CO2 at low temperatures and C2H2 at high temperatures with separation factors of 498 (CO2/C2H2) and 181 (C2H2/CO2), respectively.