Analysis of Molecular Interaction and Its Effect on Light- Harvesting and Emitting Organic Systems at the Nanoscale

Abstract

Organic electronics is a branch of modern electronics, and it deals with organic materials, such as polymers or small molecules. Its high flexibility, ease of manufacturing, low cost and environmental impact gathered huge interest from industry and academia. While there have been great progress in the area of organic electronic materials, many challenges limit the potentials of various organic systems. The intrinsic structural and electronic inhomogeneity of the solid state aggregates of organic molecules limit their performance and lower their stability. Mismatch between the light absorption and the exciton transport length in organic photovoltaic cells is the critical point of the issue. To solve this problem a better understanding of the excitation transport properties on a local level is essential. However it is difficult to probe the exited dynamics due to fast decay and short transport length of exciton. To better investigate these materials, superior spatial and temporal resolved spectroscopy is essential. In this dissertation, various spectroscopic methods have been introduced to analyze the exciton dynamics in local level. Interferometric two-photon near-field scanning optical microscopy has been introduced to show the organic macromolecular and aggregate systems assembled in different molecular structural orientation. A focus will be placed on the combination of fs-laser interferometry and NSOM microscopy. ~100fs temporal and ~50nm spatial resolution of the system efficiently highlight the structure-functional relationship, discriminate the heterogeneity and measure the coherent excited state dynamic of the molecular system aggregates. Additionally, the ultra-fast excited state behavior of selected organic electronic materials has been studied using fluorescence upconversion and transient absorption spectroscopy. These investigations inform us of how these photophysical interactions occur in several systems, including light -harvesting and -emitting systems.