Smart Hydrogen-Bonded Organic Frameworks: From Design Rules to Applications

Crystalline porous materials have evolved significantly with the advent of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), yet hydrogen-bonded organic frameworks (HOFs) represent a distinct paradigm shift from static to adaptive porosity. Unlike their coordination- or covalent-bonded counterparts, HOFs are assembled via weak, reversible hydrogen interactions, endowing the framework with intrinsic "softness" and adaptive flexibility. This unique structural nature allows for reversible transformations─such as breathing, gate-opening, and layer sliding─in response to external stimuli. In this perspective, we systematically discuss the design rules of smart HOFs, highlighting how specific flexibility mechanisms are translated into advanced functionalities across four pivotal domains. We explore how adaptive pore environments enable the discrimination of similar-sized molecules and "self-healing" capabilities in separation processes, and how structural perturbations are converted into readable optical or electrical signals for precise sensing. Furthermore, we examine the leveraging of dynamic luminescence and topological switching for smart optoelectronics and information security, as well as the utilization of stimuli-responsive drug release and biocompatibility for precision biomedical therapy. Finally, we provide a critical outlook on the future challenges regarding stability, predictability, and processability, aiming to bridge the gap between theoretical design and practical deployment of smart HOF materials.