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

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-HMIDLINE HORIZONTAL ELLIPSISN 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-HMIDLINE HORIZONTAL ELLIPSISN hydrogen bonds and & pi;-& pi; 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. Through the introduction of different pyridine derivatives into carboxylic acid self-assembly structures, abundant co-assembly structures were constructed by converting the O-HMIDLINE HORIZONTAL ELLIPSISO hydrogen bond to O-HMIDLINE HORIZONTAL ELLIPSISN or C-HMIDLINE HORIZONTAL ELLIPSISN hydrogen bonds.