This study reports a temperature-responsive recognition system for two similar gaseous guests, CO₂ and C₂H₂, using a diffusion-regulatory porous material. The system, termed flip-flop dynamic crystal (FDC-3a), features ultrasmall pore apertures and locally dynamic organic moieties that regulate gas diffusion. At low temperatures, CO₂ diffuses faster than C₂H₂, leading to preferential adsorption of CO₂ with a selectivity of 498 (CO₂/C₂H₂). At high temperatures, C₂H₂ has a higher adsorption affinity, resulting in selective adsorption of C₂H₂ with a selectivity of 181 (C₂H₂/CO₂). This temperature-dependent adsorption behavior is achieved by amplifying the rate differences between CO₂ and C₂H₂, which are controlled by the dynamic local motion of the ligand. The system demonstrates significant potential for applications in molecular machines, sensors, gas separation, and drug delivery.This study reports a temperature-responsive recognition system for two similar gaseous guests, CO₂ and C₂H₂, using a diffusion-regulatory porous material. The system, termed flip-flop dynamic crystal (FDC-3a), features ultrasmall pore apertures and locally dynamic organic moieties that regulate gas diffusion. At low temperatures, CO₂ diffuses faster than C₂H₂, leading to preferential adsorption of CO₂ with a selectivity of 498 (CO₂/C₂H₂). At high temperatures, C₂H₂ has a higher adsorption affinity, resulting in selective adsorption of C₂H₂ with a selectivity of 181 (C₂H₂/CO₂). This temperature-dependent adsorption behavior is achieved by amplifying the rate differences between CO₂ and C₂H₂, which are controlled by the dynamic local motion of the ligand. The system demonstrates significant potential for applications in molecular machines, sensors, gas separation, and drug delivery.