 This study reports the development of a temperature responsive recognition system in an artificial host guest system that can switch selectivity between two similar gaseous guests, CO2 and C2H2, by utilizing a dynamic porous crystal with flip-flop local emotive organic moiety. The dynamic local motion regulates the diffusion process of the guests and amplifies their rate differences, allowing the crystal to selectively adsorb one guest at low temperatures and the other at high temperatures with separation factors of 498, CO2, C2H2, and 181, C2H2, CO2, respectively. This article was authored by Yang Tzu, Kenichio Take, Jiu Jiu Xing, and others.