Porosity Switching in Polymorphic Porous Organic Cages with Exceptional Chemical Stability

Porous solids that can be switched between different forms with distinct physical properties are appealing candidates for separation, catalysis and host‐guest chemistry. In this regard, porous organic cages (POCs) are of profound interest because of their solution state accessibility. However, the application of POCs is limited due to their poor chemical stability. Herein, we report synthesis of an exceptionally stable imine linked (4+6) porous organic cage (TpOMe‐CDA) using 2,4,6‐trimethoxy‐1,3,5‐triformyl benzene (TpOMe) as a precursor aldehyde. Introduction of the –OMe functionality in the aldehyde provides the significant steric and hydrophobic environment around the imine bonds that protects the cage molecules from being hydrolysed in the presence of acids or bases. The electronic effect of the ‐OMe group also plays an important role in enhancing the stability of the reported POCs. As a consequence, TpOMe‐CDA reveals exceptional chemical stability in neutral, acidic and basic conditions, even in 12 (M) NaOH. Interestingly, TpOMe‐CDA exists in three different porous and non porous polymorphic forms (α, β and γ) concerning the different crystallographic packing and the orientation of the flexible methoxy groups. All of the polymorphs retain their crystallinity even after the treatment with acids and bases. All the polymorphs of TpOMe‐CDA significantly differ in their properties as well as morphology and could be reversibly switched in the presence of an external stimulus.

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