Intellectual Merit: Organic optoelectronics is a rapidly advancing field, but most studies to date are focused on measurements of thin films involving a large ensemble of molecules. The present project aims at studying how the optoelectronic properties of these systems change when the device is decreased to nano- and molecular-scales, and exploring single molecule light emitting device and optical sensing applications. Such studies will lead to new insights into charge transport mechanisms, carrier energy dissipation processes and electrode-molecule contact effects in molecular-scale junctions, determine the interplay between the charge transport and optical properties, and provide the basic knowledge and necessary skills to develop novel device applications. Broader Impact: The project will also have an important impact on a variety of other fields, including biophotonics and photosynthesis, as well as thin film-based optoelectronic devices, such as organic photovoltaics and organic light emitting diodes. In addition, it will expose engineering undergraduates to research opportunities in emerging fields. To this end the PIs will work together with the outreach program at Fulton School of Engineering and Biodesign Institute to recruit minority students. The proposed research and training activities will also help graduate students develop important teaching, management and communication skills. As part of the outreach plan, international collaborations with research groups in Germany and Japan will be developed to provide students with international experience. The interdisciplinary research has potential transformational impacts on the next-generation of scientists and engineers, and on the next-generation organic optoelectronics.
Advances in electronics and optoelectronics have relied on understanding and manipulating semiconductor materials at ever-smaller scales. The ultimate functional building blocks of devices are single molecules. Single molecule-based devices are attractive not only because their sizes, but because their properties and functions that are often completely different from the conventional semiconductor devices, which may lead to applications that the current semiconductor materials cannot achieve. To develop single molecule devices, one must understand single molecule properties, and find out ways to manipulate and measure single molecules, which are the goals of the present project. Supported by NSF, we have made significant progress in the following areas: We have developed a setup that can manipulate single molecules and measure electrical properties of single molecules. The setup allows us to characterize electrical properties of single molecules. Some of the molecules we studied exhibit the rectification effect, i.e., current flows in one direction is more easily than the opposite direction, which is in analogous to a diode widely used in today’s electronic devices. Other molecules have properties that are analogous to a transistor, another widely used semiconductor device. We also studied heat generation as a consequence of current flowing through the molecule, which is critically important for future device applications. While it is important to study molecules that are analogous to conventional semiconductor devices, such as transistors and diodes, it is also possible to perform experiments that have no parallels in conventional electronics. For example, by applying a mechanical force to a molecule bridged between two electrodes, a device known as a molecular junction, it is possible to combine the molecule's electrical and mechanical properties to control the charge transport through the junction. We have studied the electromechanical properties of different molecules as they are stretched and compressed. For the most molecules, the conductance decreases when we stretch them. However, we have also observed that the conductance of a molecule can increase by one order of magnitude by stretching. The project has provided us with basic knowledge and skills to develop single molecule-based devices. It has also led to new insights into electron transport in single molecules, which occur in many chemical and biological processes.
