Self-Assemblies And Chemical Reactions Of Nitrogen-Containing Organic Molecules On Metal Surfaces

Nitrogen-containing organic compound is widely found in nature.It is closely related to life and widely applied to medicine,dye,dynamite and other respects.In this thesis,we systematically explored the self-assembly and reaction behavior of the nitrogen-containing organic molecules under ultrahigh vacuum conditions on different crystallographic planes of a Cu substrate studied by scanning tunneling microscopy(STM).Our results suggested that different products,such as oligomers,ID linear structures,2D networks could be formed via the coordination between Cu adatoms and the dehydrogenated amino groups.Besides,this coordination interaction can lead to chiral products.Furthermore,the probability of the adjacent C-H bond activation induced by the dehydrogenation of the amino groups increased when we raised the annealing temperature.Moreover,the electrostatic interaction between the imino nitrogen atoms and Cu adatoms can be used to construct 2D networks on surfaces.Through the above study,we provided a way for the understanding of the self-assembly and reaction pathway of organic molecules on solid surfaces.The work in this thesis is mainly divided into the following three sections:1.When we deposited the precursor molecule referred to 1,3,5-tris(4-aminophenyl)benzene onto Cu(111)surface held at different temperatures,various kinds of phases could be observed.When deposited onto the surface held at room temperature(298 K),the individual molecules could be found dispersing over the entire surface,suggesting that the intermolecular interactions were not strong.When the substrate temperature was 340 K,one hydrogen atom in an amino group could be removed,and the resulting imino group was able to coordinate with one copper adatom.As a result,there existed two dimer structures.When the substrate temperature was increased to 350 K,2D metal-organic frameworks could be identified in the STM image.The inner hexagonal units showed three kinds of shapes.Combining with the result carried out by Density Functional Theory(DFT)calculations,we obtained the structural models of the three hexagonal complexes and elaborated the reason why they were observed in the porous networks with similar probabilities.This work shows the generality of the coordination between the dehydrogenated amino groups and the copper adatoms and provides a new way for constructing metal-organic frameworks on surfaces.2.We systematically explored the adsorption behavior of the products formed by the dehydrogenated molecules coordinating with the copper adatoms on(111)and(100)of a Cu substrate.The two-fold symmetrical precursor molecules referred to as 4-amino-p-terphenyl and 4,4'-diamino-p-terphenyl have different numbers of amino groups.The result showed that there both existed two chiral packing strategies among the two products formed via the coordination between the dehydrogenated amino groups and Cu adatoms at the annealing temperature of 340 K.And the enantiomers were oriented at an angle of±32° relative to a set of the high-symmetry crystallographic directions.On the other hand,we found that large-area 2D porous networks could be formed by the electrostatic attraction between N,N-diphenylbenzidine and Cu adatoms on Cu(111).Among different domains,there were two chiral packing strategies as well.3.Upon annealing the sample at a certain temperature,the adjacent C-H bond of the amino group in 4-amino-p-terphenyl could be broken.Analyzing the number of a great amount of products,we found that the probability of the selective C-H activation could be increased when the annealing temperature rose.However,the desorption and side reactions obstructed the complete construction of products formed via the selective activation of C-H bonds.