Synergistic modulation of steric hindrance and isomerization space for enhanced photo-regulated performance of metal-organic polyhedra

Abstract

As an emerging class of smart materials, photoresponsive metal-organic polyhedra (PMOPs) have garnered growing attention owing to their modular architectures, tunable functionality and remote addressability. However, severe aggregation in the solid state compromises the photoresponsiveness; additionally, their photo-regulated performances (e.g. on adsorption) remain to be improved. Here we report a synergistic modulation strategy that concurrently engineers steric hindrance and isomerization space to construct a novel Rh-based PMOP, (tBu-Azo)(LA)MOP. This cage architecture comprises a sterically hindered azobenzene unit (tBu-Azo) and a long alkyl-chain spacer (LA), where the tert-butyl groups are designed to enhance the manipulation on open metal sites, while the LA ligands are designed to provide essential intermolecular spacing for efficient photoisomerization. Upon visible-/UV-light irradiation, the photoresponsive units in (tBu-Azo)(LA)MOP undergo reversible trans-cis isomerization with markedly improved photo-regulated performance. Consequently, a 49.7% change in propylene uptake is achieved, far surpassing that of the comparator (Azo)MOP assembled from unmodified azobenzene ligands in the absence of LA (17.1%). The outstanding photo-regulated performance, combined with high adsorption capacity, positions (tBu-Azo)(LA)MOP among the top-performing photoresponsive adsorbents reported to date. Density-functional-theory calculations are consistent with the interpretation that the trans-cis isomerization may effectively modulate the binding strength between active sites and C₃H₆. This work offers a viable avenue for the design of high-performance photoresponsive materials with broad applicability.