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.