Progress in scanning tunneling microscopy research on the regulation of carboxylic acids and their derivatives assembled structures by pyridine
The supramolecular self-assembly of organic functional molecules on the solid interfaces is a fundamental support for numerous basic and applied research fields.Therefore,the mechanism of self-assembled processes has attracted extensive interest for decades,which provides a theoretical basis for constructing functional nanostructures at the molecular level.Scanning tunneling microscope(STM)can achieve images with a truly atomic scale resolution based on the tunneling current between probes and surfaces.The development of STM opens up a new way to explore the structure and properties of self-assemblies on the two-dimensional(2D)surface.Due to the high-directionality and saturation of hydrogen bonds,the 2D nanostructures driven by intermolecular hydrogen bonding interactions have been widely developed.One of the typical hydrogen bonded networks is formed by carboxylic acid through O-H…O interactions of carboxyl groups between adjacent molecules.However,because of the molecular structure and solvent co-adsorption phenomena at the solid/liquid interface,most of these systems currently studied are homomolecular systems.The reliable preparation method of two-component systems requires the stability of the two-component system exceeds that of any other single-molecular system.The N atom of pyridine is a good acceptor of hydrogen bonds,which has an unpaired electron.Current research shows that carboxyl groups as donors and pyridine as acceptors can preferentially form a binary system based on hydrogen bonds in specific systems.This review summarizes the recent progress in the regulation of carboxylic acids and their derivatives self-assembled structures by pyridine derivatives using STM technology,focusing on how the number and position of functional groups and substituent group of pyridine and carboxylic acid affect the binary systems.Moreover,the self-assembly behavior and co-assembly with pyridine derivatives of rigid,planar and symmetric aromatic carboxylic acids are significantly different from those with low symmetry.The flexible alkyl side chains have structural orientation abilities which can work as molecular templates to accommodate pyridylethynyl derivatives with different sizes and shapes.Fluorination of carboxylic acids can prevent their self-assembly and advantages in the construction of binary networks with different pyridines.Carboxylic acid derivatives containing N heterocycles also show specific co-assembled modes attributed to different strengths of hydrogen bonds donors and acceptors.Carboxyls help porphyrin derivatives form an ordered arrangement through hydrogen bonds and make them can be regulated by different kinds of pyridine.In conclusion,rich binary nanostructures have been constructed which provide effective means for the fabrication and regulation of 2D multicomponent supramolecular assembled structures.However,there are still many shortcomings in this field that require further development.Firstly,we can continue to broaden the basic building blocks of surface nanostructures.For example,we can increase the number of pyridine groups and compare the proportion of O-H…O and O-H…N hydrogen bonds to further deepen the understanding of the co-assembled structure formed by pyridine and carboxylic acids.Secondly,the current understanding of the process and mechanism of surface self-assembly is still insufficient and we are unable to predict the assembled structure accurately.Thirdly,we hope that we can develop more mature surface detection technologies and promote the practical applications of supramolecular self-assembled structures.
NETL
NSTL
万方数据
维普
