All-visible-light-responsive porous aromatic frameworks manipulate CO2 uptake by reversible bulk isomerization of azobenzene pendants

Embedding light-responsive small molecules in a porous solid is a promising strategy to achieve dynamic control over material properties. Powering these systems with low-energy photons is essential for their future applications, since visible light, compared to UV light, is less damaging and offers more selective isomerization with higher penetration depth. However, the construction of visible light-responsive porous materials remains a significant challenge. Here, we report the construction of a series of visible-light-responsive porous aromatic switchable framework materials grafted with o-fluoroazobenzene pendants (Azo-PSFs). The materials exhibit high microporosity and reversible photoswitching upon irradiation with visible light. The highly robust materials can be cycled between two distinct states multiple times without showing any photo fatigue or decomposition. Remarkably, solid-state NMR revealed that the azobenzene moiety undergoes reversible bulk isomerization in the framework. The isomerization of azobenzene within the framework is associated with substantial changes in adsorption capacity and CO2 uptake-release by the material. This work presents the example of visible-light-triggered bulk isomerization in an azobenzene-based porous material, providing a benchmark characterization of photoresponsive systems and paving the way for the future advancements in light-driven materials.