In recent years, combining the first principle of calculation with scanning tunneling microscope (STM) and atomic force microscope (AFM) experiments has become a powerful means to study surface physics and chemical processes at the atomic and molecular levels. On the basis of achieving small molecule or even single atom level manipulation and surface chemical reactions, novel physicochemical properties at the atomic scale can be further studied.
surface synthesis is a synthesis method that has attracted much attention in recent years. Using the catalytic and confined domain effects on the surface of metal single crystals, a large number of low-dimensional functional nanomaterials that cannot be synthesized by traditional wet chemistry methods have been synthesized. Du Shixuan, a researcher at the Institute of Physics, Chinese Academy of Sciences/Beijing National Research Center for Condensed Matter Physics, etc., has achieved a series of internationally cutting-edge research results in this field. In 2014, they combined first-principle calculations with STM experiments to confirm for the first time that the cyclized trimerization addition reaction of alkyne molecules occurring on the Au surface is a two-step reaction of [2 + 2 + 2]. At the same time, they found that the surface domain-limiting effect effectively improves the selectivity of the reaction. Related work was published in J. Am. Chem. Soc. 136, 5567 (2014). Recently, they collaborated with H. Fuchs, a professor at the University of Munster, Germany, to discover the modulation effect of different metal substrates on the surface Ullmann reaction. Related work was published in Chem. Commun. 54, 9305 (2018); in addition, they collaborated with Lawrence Berkeley National Laboratory to study the mechanism of self-assembly of surface metal organic nanoparticles and nanocrystals to form two-dimensional superstructures, and related work was published in Angew. Chem. Int. Ed. 57, 13172 (2018). The synthesis of these fine structures shows that the substrate surface and the own structure of functional molecules are precisely selective in the activation and breaking of different functional groups . Controllable selective functionalization of
organic molecule is of great significance to realize the precise structure of low-dimensional materials at the atomic scale. However, achieving selective activation of similar groups in organic molecules, especially those of equivalent groups in symmetric molecules, is a historic problem in traditional chemical synthesis.
Recently, Du Shixuan (co-corresponding author) and Professor Chi Lifeng of Soochow University and Professor André of Giesen University in Germany Schirmeisen cooperated to achieve the selective activation of two identical amino groups in DATP through the adsorption of 4,4″ amino -p-terbyl (DATP) molecules on the surface of Cu (111), and the molecular long axis is along the [ 11-2] and its equivalent crystal direction, in the AFM image, the molecule has a blurred feature, and the mirror symmetry of the molecule is broken (Figure 1). Chemical bond resolution AFM characterization combined with first-principle calculation reveals that the lattice mismatch between DATP molecules and Cu(111) causes two equivalent amino functional groups in the molecule to adsorb at different positions on the copper surface, one end adsorbs at the apical position of the copper atom and the other end adsorbs at the hollow position of the Cu atom on the surface (Figure 3). The amino group adsorbed at the apical position is closer to the copper surface than the amino group at the other end, and has stronger interaction with the surface, so the degree of activation is stronger, making it appear non-stable under the influence of the needle tip, and preferentially binds to the 2-tribenzaldehyde (TPCA) molecules with hydrogen bonds (Fig. 5). When the DATP molecule is adsorbed on the Au(111) surface, the molecules remain mirror-symmetric because the length of the molecule matches the base lattice, and the amino adsorption positions at both ends are The same, so the activation degree of amino groups at both ends is the same (Figure 4). The molecular asymmetric adsorption caused by the lattice mismatch between the DATP molecule and Cu(111) surface and the enhanced activity of specific functional groups provide a widely used approach for the selective functionalization of equivalent groups in symmetric molecules and a new idea for asymmetric chemical reactions on the surface. The related work of
was published in "Nature Communications" (Nature Communications9, 3277 (2018)), this work was supported by the National Natural Science Foundation of China-Germany Cooperation Program, the Ministry of Science and Technology and the Chinese Academy of Sciences.
Figure 1. Two adsorption configurations of DATP molecules on the surface of Cu(111).
Figure 2. Kinetic analysis and energy barrier of observed jump mechanisms.
Figure 3. The first asymmetric adsorption configuration of DATP molecules on the surface of Cu(111).
Figure 4. The second symmetrical adsorption configuration of DATP molecules on the surface of Cu(111) and Au(111).
Figure 5. Self-assembly of DATP and TPCA molecules.
