Photoresponsive metal-organic polyhedra in metal-organic frameworks: Achieving real responsiveness

Photoresponsive metal-organic polyhedra (PMOPs) show controllable properties in a broad range of applications, such as adsorption, catalysis, and molecule inclusion. However, the aggregation of bulk PMOPs leads to their inaccessibility of inside nanocages and low regulatory efficiency by light. Herein, a new PMOP (PM2L4) with pendant azobenzene units was synthesized and dispersed into the pores of the metal-organic framework (MOF, PCN-333). The obtained PM2L4@MOF composites show improved CO2 uptake and photoresponsive efficiency. Upon visible-light irradiation, the azobenzene groups stay in the trans state where CO2 molecules can freely enter the nanospace of PM2L4. Nevertheless, upon ultraviolet (UV)-light irradiation, the azobenzene groups transform to the cis state, which hinders the entrance of CO2 to the nanospace of PM2L4. In addition, UV/visible light irradiation can facilitate the reversible cis-/trans-isomerization of the azobenzene groups of PM2L4. The adsorption variation of CO2 captured by PM2L4@MOF composite under light is 15.5%, which is much higher than that of bulk PM2L4 (5.9%). We believe that the findings of this study will provide insights into the potential of PMOPs and may inspire the development of exquisite strategies to efficiently control adsorption processes.

Automated summary

In this study, a new type of photoresponsive metal-organic polyhedra (PMOP) with pendant azobenzene units was successfully synthesized and dispersed into a metal-organic framework (MOF), resulting in improved CO2 uptake and controllability. Visible light allows CO2 molecules to freely enter the nanospace of PMOP, while ultraviolet light prevents their entrance. Additionally, UV/visible light irradiation enables the reversible cis-/trans-isomerization of the azobenzene groups in PMOP. The adsorption variation of CO2 captured by the PMOP@MOF composite under light is 15.5%, significantly higher than that of bulk PMOP (5.9%). These findings provide insights into the potential of PMOPs and inspire the development of efficient strategies for controlling adsorption processes.