Recognising timescale as an adjustable dimension in porous solids provides a new perspective to develop novel four-dimensional framework materials. The deliberate design of three-dimensional porous framework architectures is a developed field; however, the understanding of dynamics in open frameworks leaves a number of key questions unanswered: What factors determine the spatiotemporal evolution of deformable networks? Can we deliberately engineer the response of dynamic materials along a time-axis? How can we engineer energy barriers for the selective recognition of molecules? Answering these questions will require significant methodological development to understand structural dynamics across a range of time and length scales. P orous framework materials offer outstanding functionality due to their wide range of tuneable building blocks and ultrahigh porosity 1-5. The integration of functions, such as chemisorptive, redox, optically or catalytically active centers, encapsulated drugs, enzymes, nanoparticles, and more, has led to the discovery of metal-organic framework (MOF) applications in gas separation, CO 2 sequestration, gas storage, catalysis, optics, and sensing, and a roadmap for integration into electronic systems has even been proposed 6-12. The chemistry of three-dimensional (3D) porous framework materials, connecting nodes and linkers through a variety of chemical bonds is enormously rich 13,14. While decades ago, rationalization was aided by topology analysis and isoreticular expansion 15,16 , in the age of digitalization computer-aided design plays a crucial role in predicting millions of new 3D structures and their properties 17-19. The serendipitous discovery of an adsorption induced structural transformation in a network nowadays termed ELM-11 20 stimulated researchers and laid the foundations for exploring novel dynamic phenomena in porous frameworks. Like enzymes, structural changes are stimulated by guest molecules intruding into the porous frameworks leading to macroscopic volume changes of up to 200-300%. The adaptive change of pore size is a fascinating feature, but a selectivity comparable to that of enzymes has not been reached yet. Emerging applications of adaptive porous materials Porosity switching in the crystalline solid state represents a unique phenomenon observed only in a limited number of porous materials 21-25. This flexibility was predicted in 1998 for MOFs by Kitagawa and coworkers, and later termed "3 rd Generation MOFs" 25-27. These materials are characterized by dynamic features of the framework structure and are also named "soft porous crystals" (SPCs). We briefly account here a few remarkable applications of the dynamic frameworks reported today as the premise for our following perspective (Fig. 1). In gas storage applications, the pore closing upon desorption provides almost ideal deliverable capacity, a key advantage compared with rigid adsorbents 28. More importantly, for gas separations, the selective response of the porous host in adapting the pore shape to a reco...