Theoretical Investigation On The Structures And Properties Of Molecular Switch And Two-dimensional Material

Over the past few decades,information technology has dramatically changed the lifestyle of people.Meanwhile,the growing need to store and process data has largely stimulated the search for molecular switches as tiny as a molecule and storage elements.Molecular switches can be switched from one state to another by external stimuli,similar to macroscopic machines,so they can be controlled to achieve many functions.Designing new molecular switches with excellent physical properties will hopefully expand the field of molecular switches.After the discovery of graphene with a Dirac cone,the exploration of graphene-like two-dimensional materials has also been developed rapidly in material research.Especially in recent years,many studies on honeycomb borophenes have been reported.But the stabilization of honeycomb borophenes was achieved only on the surface of aluminum experimentally.In this paper,a new molecular clam switch and two-dimensional borophene material were designed,respectively.For the molecular clam switch,it was focused on analyses of conformational evolution of system with external electric field and its potential applications.For the two-dimensional borophene material,based on the first principles calculations,a new two-dimensional structure Li₂B₂ were predicted and its potential applications were explored.Specific research results are as follows:1.Most molecular switches are performed by external chemical stimuli,which limits application in the field of molecular electronics.In this paper,a new kind of molecular switch was obtained by using a physical method of external electric field.we chose a small Janus molecule with a large HOMO-LUMO gap value and dipole moment,so its dimer is easy to be manipulated by the external electric field and become a molecular switch.This switching process is reversible and like a clam behavior,so this switch is named as the molecular calm switch.There is an interlayer multiple hydrogen bond altering mechanism in the switching,that is,the breaking and forming of multiple hydrogen bonds.This distinguishes the mechanism of the breaking and forming of strong chemical bonds in some switchings.Importantly,the clam switch may serve as an electric information storage unit due to a great electric dipole moment contrast between Closed state and Open state in the switching process.This is different from widely used magnetic information storage unit and a new way of storing information.The reading,writing,and erasing of binary information on the storage unit are easy.Finally,it was found that the graphene-based fragment Janus dimer can also serve as a molecular clam switch.This work proposes a new molecular switch prototype and a potential electric information storage unit,which is expected to provide a new idea for field of artificial molecular machines and molecular electronics.2.Compared with three-dimensional materials,two-dimensional?2D?materials have attracted much attention for their unique optical,electronic and mechanical properties.In recent years,the research on borophenes has become one of hot topics,especially reports on the stabilization of graphene-like borophenes are rare.In this paper,A new two-dimensional honeycomb borophene?Li₂B₂?exfoliated from the substrate is reported.Firstly,based on molecular orbital analyses,two Li atoms were chosen to stabilize a B₆ ring and obtained a series of Li-doped honeycomb borophene fragments,namely Li₂B₆,Li₆B₁₃ and Li₁₄B₂₄.Remarkably,the Li₁₄B₂₄ including the planar polyanion B₂₄^14-,can serve as an electron reservoir unusually exhibiting two different behaviors of electron donor and electron acceptor.Secondly,the Li₂B₂ sheet was obtained and demonstrated to be thermally and mechanically stable by material property calculations.Importantly,we calculated the energy band and superconducting properties,indicating that the Li₂B₂ sheet is not only a metal 2D material with a Dirac cone,but also an intrinsic superconductor with the superconducting transition temperature T_c⁶.2 K.This work enriches the research of two-dimensional superconducting materials.