Next Generation of CO2-Responsive Materials Constructed by Dynamic Gas-Bridged Chemistry

Stimuli-responsive materials, which undergo reversible structural/phase transitions in response to stimuli, represent one of the most active and appealing research areas in intelligent materials. Compared to other external cues, carbon dioxide (CO2) as a unique gaseous stimulus offers distinct advantages, including being green and chemical-waste-free and offering ease of introduction and removal and spatiotemporal control, and exhibits promising applications in diverse fields such as CO2 capture and utilization, gas sensors, biomedicines, and smart interfaces. Despite substantial advancements, conventional CO2-responsive systems predominantly rely on a Brønsted acid-base mechanism by which tertiary amine or nitrogen-bearing basic groups react with hydrated CO2. Since this mechanism entails the participation of H2O molecules and the generated carbonic acid (H2CO3) is inherently weak and metastable, the reactive process compromises on slow response rates, short lifetimes, and heavy environmental dependence, which highly impede its utility in smart control and functional switching. In this context, the molecular principle behind CO2-responsive materials desires an urgent breakthrough. Building on the foundation work from our research, this Account presents a concept of dynamic gas-bridged chemistry (DGB) and leverages it to realize a second CO2 response mechanism. This mechanism can avoid the Brønsted acid-base reaction (CO2 + H2O + R3N ⇄ R3NH+ + HCO3-) and involves direct dynamic binding between CO2 gas and a triarylborane/triarylphosphine-based frustrated Lewis pair (FLP) to form a dative gas-bridging structure (CO2 + Ar3B + Ar3P → Ar3P-CO2-BAr3). DGB has two advantages: (i) it belongs to a unique class of dynamic covalent bonding that endows the materials with favorable stability while maintaining reversible dissociation, and (ii) its binding kinetics (10-30 s) conquers the limit of response rate in first-generation CO2-sensitive materials. In this Account, we first introduce the chemical essence of DGB for replying to CO2 and highlight its noncanonical properties distinct from common dynamic bonds, called "gas-bridge metathesis" and "gas-bridge semiactivation", which respectively become the foundation of CO2-regulated self-assembly and CO2-involved efficient catalysis. Second, we summarize the advance of a new generation of CO2-responsive materials on the basis of the DGB principle, including how to exploit CO2 gas as a connector to construct multidimensional materials, use CO2 as a trigger to manipulate self-assembly kinetics and reshuffle material architectures, and establish CO2-involved porous and nanomaterial platforms for high-performance gas catalysis. Finally, we extend this DGB-based CO2-responsive mechanism to a broad spectrum of gas molecules and offer an outlook on the future challenges and possible directions in gas sensors and gas-gated electronics.