Bidirectional Phase Transformation of Supramolecular Networks Using Two Molecular Signals.

Reversible control of molecular self-assembly is omnipresent in adaptive biological systems, yet its realization in artificial systems remains a major challenge. Using scanning tunneling microscopy and density functional theory calculations, we show that a 2D supramolecular network formed by terthienobenzenetricarboxylic acid (TTBTA) can undergo a reversible structural transition between a porous and dense phase in response to different molecular signals (trimethyltripyrazolotriazine (TMTPT) and C). TMTPT molecules can induce a phase transition from the TTBTA honeycomb to the dense phase, whereas a reverse transition can be triggered by introducing C molecules. This response stems from the selective association between signal molecules and TTBTA polymorphs. The successful realization of reversible molecular transformation represents important progress in controlling supramolecular surface nanostructures and could be potentially applicable in various areas of nanotechnology, including phase control, molecular sensing, and "smart" switchable surfaces.