Design of Organic Materials with Unique Supramolecular Assembly for Optical, Electronic, and Biomedical Applications.

Abstract

Rational material design is inevitable to fully realize the properties of organic conjugated materials in applications, by regulating their intermolecular packing as well as intramolecular properties. In this dissertation, molecular design strategies to control interactions and assemblies of organic conjugated materials are systematically investigated, which enables unique optoelectronic properties for various optoelectronic applications. In Chapter 2, a molecular design to control intermolecular interactions renders a unique thermally stable supercooled liquid and its shear-triggered lighting-up crystallization with 25-times fluorescence enhancement. The origin of the unique property is systematically scrutinized. Furthermore, possible biosensor application is proposed by demonstrating highly sensitive crystallization of the supercooled liquid by living cell attachment. Insightful design consideration for both intrachain and interchain properties is also critically important for conjugated polymers (CPs). In Chapter 3, molecular design of CPs’ main and side chains is logically investigated to regulate optical properties. Tailored CPs exhibit identical color in solution manifesting the same intramolecular optical properties by conjugated backbone design. Contrastingly, they show distinct color gradation in the solid state due to the coined intermolecular packing propensity difference through side chain design. Latent optical information encoding using CPs as security inks is demonstrated, which reveals and conceals hidden information upon CP aggregation/deaggregation. Furthermore, expansion of the design principles for efficient CP alignment is investigated (Chapter 4). Realization of CP alignment largely affects optoelectronic applications of CPs since it is inevitable to fully utilize CPs’ anisotropic properties in devices. Previously identified molecular design rules to realize directed CP alignment are evaluated, and more detailed design factors are additionally revealed. The properties of organic conjugated materials are also influenced by environmental factors, including characteristics of a substrate and solvent molecules. In Chapter 5, a novel optical sensor is devised based on controlled subtle interaction differences between substrates, fluorescent sensory molecules, and analyte solvents. The highly selective sensor array can clearly distinguish physicochemically similar liquids; ethanol, methanol, ethylene glycol, and water. The thoroughly discussed molecular design principles in this dissertation depict an insightful picture on how unique optoelectronic properties of conjugated organic molecules and polymers can be designed and fully utilized in various applications.