Dynamic Supramolecular Template: Multiple Stimuli-Controlled Size Adjustment of Porous Networks

Dynamically switchable porous networks offer exciting potential in functionalizing surfaces. The structure and morphology of the networks can be controlled by applying external stimuli. Here, a dynamic supramolecular template assembled by 1,3,5-tris(4-carboxyphenyl)benzene (BTB) is successfully achieved at the liquid-solid interface by applying two external stimuli simultaneously. Upon varying the concentration of BTB solution together with switching the polarity of the sample bias, self-assembled monolayers (SAMs) undergo phase transitions twice: an immediate transition from a compact structure to a macroporous (honeycomb) structure as a response to the change in the electric field and a fast-changing transition from the macroporous to a microporous (oblique) structure. With saturated BTB solution, however, the initial compact structure can only transform into the oblique structure after switching the polarity of the sample bias without the appearance of a honeycomb structure. The different phase transitions suggest that the dynamic supramolecular template can only survive at a specific concentration range and is obtainable by performing multiple stimuli simultaneously. Interestingly, introducing a guest molecule to the system can adjust the phase transition process and effectively stabilize the honeycomb structure of BTB. The flexibility associated with the porous networks renders it a dynamic supramolecular template for guest binding.