Encapsulation and Immobilization of Functional Molecules Using Cage-Like Porous Frameworks

To exhibit the intrinsic functions of functional molecules not only in solution but also in solid materials, we have developed immobilization methods that use porous frameworks as support materials. Conventionally, functional molecules are immobilized via impregnation into porous frameworks using physisorption or grafting on the pore surfaces using chemical bonds. However, these methods can lead to leakage during use and performance degradation owing to structural modifications for immobilization. Recently, cage-like porous frameworks have attracted attention as support materials, and a novel method (encapsulation), where the functional molecules are reliably confined into the pores, has been discovered. The narrow windows of cage-like porous frameworks physically confine functional molecules into their pores, thereby suppressing leakage without chemical bonds and preserving the intrinsic function of the molecules after immobilization. In this perspective, we comprehensively summarize various encapsulation methods and developments of functional solid materials based on encapsulation and outline their future prospects.