Control the Charge Transport Properties of Amine-functionalized Molecular Wires by pH, Electric Field, and Supramolecular Interactions

Amine is an important chemical group that appears ubiquitously in biological macromolecules including nucleic acids and proteins, as well as in synthetic organic materials such as approximately 42% of drugs and drug candidates. Understanding the fundamental role that amines play in constructing the physical properties that amine-containing materials exhibit is critically relevant in biomedicine and materials chemistry. However, there remain open questions about the specific electronic contributions of amines to the total transport properties of a material. For example, to control the electronic characteristics of amine-functionalized compounds by external stimuli is still a work in progress. Molecular junctions have emerged as a powerful platform for investigating the response of organic electronic materials to external stimuli at the single molecule level. Furthermore, this experimental approach allows us to relate the materials’ electronic and mechanical properties to their chemical composition, three-dimensional structures, and conformational dynamics. In this research, new molecular wires that are functionalized by amine groups will be implemented for constructing electronic circuits, however, the research focus is on how the electronic properties of these molecular wires will change upon a change in the environmental control. First, amines will be incorporated as chemical linkers, backbones, or side groups in a series of molecular wires, and single molecule conductance of these molecular wires under protonated and deprotonated states will be determined. Second, a dynamical response of single molecule conductance of amine compounds to a varying bias voltage and pH will be characterized, allowing us to probe the interplay between the two external controls. Next, host-guest complexes formed between a macrocycle and an amine-containing molecular wire will be attached to gold electrodes for determining whether and how the supramolecular interactions impact charge transport at nanoscale. Specific tuning of the supramolecular interactions in molecular junctions will be achieved by a modulation of the environmental pH. Last, novel functional molecular units will be explored. This project seeks to develop new chemical strategies and theories underlying the electronic response of amines to various external stimuli through the design and measurements of a series of structurally diverse amine compounds. The fundamental knowledge generated by this research will contribute to the general understanding of molecular electronic structures, nanoscale electrochemistry, and supramolecular assembly.