Positional selectivity of reversible azomethine condensation reactions at solid/liquid interfaces leading to supramolecule formation

• Position selective azomethine reactions on a surface were found as supramolecular reaction.
• The reaction mechanisms were elucidated visually using in situ STM at the liquid–solid interface.
• The highly position selectivity was achieved by bonding and simultaneous self-assembly.

We used in situ scanning tunneling microscopy to investigate the formation of two-dimensional supramolecules by means of reversible azomethine condensation reactions between aqueous 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and terephthaldicarboxaldehyde (TPA) or benzaldehyde (BA) at the solid/liquid interface of an iodine-modified Au(1 1 1) surface. A nanomesh and a close-packed array were formed by the reaction of TAPP with the dicarboxaldehyde. Formation of these structures was driven by Schiff base (azomethine) bonding and simultaneous self-assembly controlled by adsorption and condensation equilibria. Surface cross coupling between TAPP and the monocarboxaldehyde (BA) formed highly ordered adlayers consisting solely of TAPP symmetrically disubstituted with two BA molecules attached at diagonally opposite corners. The position selectivity was achieved through simultaneous coupling reaction equilibria and the thermodynamic self-assembly.

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