A temperature-responsive porous material, FDC-3a, was developed to switch the recognition selectivity between two similar gaseous guests, CO₂ and C₂H₂, by regulating gas diffusion. The material features ultrasmall pore apertures with flip-flop motion of organic ligands, enabling dynamic control over gas diffusion rates. At low temperatures, CO₂ is preferentially adsorbed due to its faster diffusion rate, while at high temperatures, C₂H₂ is selectively adsorbed because of its higher affinity. This temperature-dependent selectivity was achieved without altering the host-guest affinity, demonstrating a novel approach to switchable molecular recognition. The material exhibited high separation factors of 498 (CO₂/C₂H₂) and 181 (C₂H₂/CO₂) at 240 K and 320 K, respectively. The study highlights the potential of dynamic porous materials for applications in gas separation, molecular machines, sensors, and drug delivery. The mechanism involves the regulation of gas diffusion through the dynamic pore system, which amplifies the rate differences between CO₂ and C₂H₂, enabling temperature-switched selective adsorption. The results demonstrate the feasibility of achieving switchable molecular recognition in artificial systems, overcoming the thermodynamic limitations of traditional host-guest interactions.A temperature-responsive porous material, FDC-3a, was developed to switch the recognition selectivity between two similar gaseous guests, CO₂ and C₂H₂, by regulating gas diffusion. The material features ultrasmall pore apertures with flip-flop motion of organic ligands, enabling dynamic control over gas diffusion rates. At low temperatures, CO₂ is preferentially adsorbed due to its faster diffusion rate, while at high temperatures, C₂H₂ is selectively adsorbed because of its higher affinity. This temperature-dependent selectivity was achieved without altering the host-guest affinity, demonstrating a novel approach to switchable molecular recognition. The material exhibited high separation factors of 498 (CO₂/C₂H₂) and 181 (C₂H₂/CO₂) at 240 K and 320 K, respectively. The study highlights the potential of dynamic porous materials for applications in gas separation, molecular machines, sensors, and drug delivery. The mechanism involves the regulation of gas diffusion through the dynamic pore system, which amplifies the rate differences between CO₂ and C₂H₂, enabling temperature-switched selective adsorption. The results demonstrate the feasibility of achieving switchable molecular recognition in artificial systems, overcoming the thermodynamic limitations of traditional host-guest interactions.