Abundant two-dimensional hydrogen-bonded co-assemblies of tetracarboxylic acid derivatives and pyridine derivatives studied by means of scanning tunneling microscopy

Abstract

In this study, the abundant co-assemblies of three rigid pyridine derivatives (PDPD, BisPY and TPYB) and tetracarboxylic acid (H₄BTY) are constructed and explored with the assistance of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. By examining the self-assembly of H₄BTY and co-assemblies of H₄BTY and three different pyridine derivatives, the driving mechanisms of those assemblies are contemplated. Firstly, H₄BTY self-assembles into a quadrilateral structure at the interface and then the self-assembled structure exhibits various responses when different pyridine derivatives (PDPD, BisPY and TPYB) are added. The bipyridine PDPD molecule with a shorter conjugate length constructs a classical acid–pyridine–acid two-dimensional co-assembly structure by forming O–H⋯N hydrogen bonds. As for the longer bipyridine molecule BisPY, a novel acid–pyridine–pyridine–acid two-dimensional co-assembly structure is formed at the interface via O–H⋯N hydrogen bonds and π–π interaction. With regard to the tripyridine molecule TPYB, three pyridine groups interact with a carboxyl group or a phenyl group, and finally three different co-assemblies are formed at the interface. Such structural regulatory behaviors may be ascribed to the different intermolecular and intramolecular interactions of co-assemblies. The regulations of pyridine derivatives on carboxylic acid assembly structures could be advantageous to the construction of functional nanostructures and the explorations of co-assembly mechanisms in molecular nanostructures.