| In 1974,American scientists Aviram and Ratner first proposed the theoretical model of single-molecule rectifier,which aroused the interest of a wide range of scientific scholars in the study of single-molecule devices.In the past two decades,the rapid development of conductivity characterization techniques such as STM-BJ and MCBJ has provided a rich experimental platform for the construction and research of single-molecule devices.Using the above techniques,researchers can efficiently construct ’ electrode-molecule-electrode ’ single molecule junctions and characterize their electrical properties,thus laying a foundation for the development of functional single molecule devices.Functional molecules are the core part of single-molecule devices,and molecules containing radicals have received extensive attention due to their special electrical and magnetic properties.However,research on single molecules based on radical molecules is rare.The main reason is that the chemical properties of radicals are extremely active,and it is difficult to form environmentally stable molecular devices.To face this challenge head-on,in this thesis we design and synthesize a series of molecules with stable organic nitro nitroxide radical units as functional components of molecular wires,and we further construct stable singlemolecule conductance devices around these molecules to study the electrical transport properties of radical molecules in single-molecule junctions.In the second chapter,we designed and synthesized a series of molecular wires based on carbazole derivatives as the skeleton.By introducing radical units into their side chains and using the scanning tunneling junction(STM-BJ)technique,the singlemolecule conductance properties of these molecules were studied.Further,through comparative studies,we mainly discussed the effect of radical introduction on molecular conductance and combined with theoretical calculations to explore its essential reasons.In the third chapter,we designed and synthesized a series of asymmetric pyridine derivatives molecular wires,and discussed the influence of the introduction of stable radicals on the molecular conductance through comparative studies.Further,we performed an I-V test on the molecular wire,and found that the conductance value was significantly asymmetric with a significant single-molecule rectifier effect.In addition to studying the single-molecule conductance properties of radical molecules,in order to further study the structure-activity relationship of free radical molecules,in the fourth chapter,we designed and synthesized a series of molecules,and used different conjugated molecular skeletons as coupling units of diradical molecules systems.We made an in-depth study of structure and the spin-coupling interaction of diradicals has been explored in depth.We first designed a diradical molecule with a donor-acceptor(D-A)conjugated backbone as a coupling unit,and used the charge polarization between D-A to study its effect on the spin coupling between two radicals. |
