Development of bis-bipyridinium and anthracene carboxyimide-based stimuli-responsive soft matter
This thesis focuses on the design and synthesis of an array of novel amphiphilic and polymeric molecules as precursors for developing dynamic stimuli-responsive supramolecular materials by harnessing the competency of non-covalent interactions. Over the past decades, bipyridinium-based derivatives have gained tremendous attention due to their applicability as functional units in tunable supramolecular complexes. The innate propensity of functionalized bipyridinium salts to serve as a ?-electron deficient acceptor allows them to undergo ?-? stacking donor-acceptor CT interactions in the presence of ?-electron rich organic molecules. This characteristic feature was employed to develop novel bipyridinium-functionalized amphiphiles and bio-polymeric materials that are capable of engaging in molecular recognition with and facilitating the extraction of melatonin, a neurotransmitter from water. The first project reports the design and development of heptyl and glycol-bridged bis-bipyridinium-based gemini amphiphiles that can undergo template-directed self-assembly. Previous studies indicated that the electrophilic aromatic nature of tetra-cationic bis-bipyridinium gemini amphiphiles can be exploited to form ?-? stacking charge-transfer interactions with ?-electron rich molecules. Thus, in an effort to establish structure-property relationships and understand the effect of the bridging unit, varied bridged bis-bipyridinium gemini amphiphiles were synthesized. They were investigated for their use of melatonin as a template for directed self-assembly processes. The charge-transfer interactions between the units lead to absorption band formation in the visible region of the electromagnetic radiation that can be exploited for various material applications. Upon comparing, the two derivatives in detail, their micellization behavior, surface properties, thermodynamic parameters, UV-Vis absorption, and micellar size exhibited similar characteristics. However, the heptyl-bridged gemini amphiphile responded to templation much more strongly, while the glycol-bridged gemini amphiphile exhibited higher solubility, they both portrayed excellent amphiphile and surface-active characteristics. The second part of this work focuses on employing ?-electron deficient bipyridinium units to design and process functional lipoic ester-based polymeric materials for the indole-base molecular targets from water. A series of lipoic-ester based-bipyridinium functionalized polymers with varying alkyl tail lengths were developed and studied to determine structure-property correlations and analyze their material characteristics. Out of the eight-novel functionalized polymeric materials, bipyridinium-bridged lipoic ester polymer (BLEP) formed polymeric sheets while nonyl-bipyridinium-functionalized lipoic ester polymer (9C-BFLEP) formed coacervates in water. Both materials showed comparable and acceptable efficiency in adsorbing melatonin out of solution by harnessing ?-? stacking charge-transfer interactions in conjugation with the hydrophobic effect. This approach provided a quick and promising method for the remediation of indole-cored molecules from water. Lastly, an anthracene carboxyimide derivative was synthesized with the ability to undergo a photo-induced [4+4] cycloaddition dimerization process. The dimerization can easily be reversed upon heating. The compound was found to be able to have a special feature that allows them to undergo single crystal-to-single crystal photo-dimerization upon exposure to UV light. This controlled switchable characteristic property of anthracene carboxyimide are unique and can be utilized for developing tunable molecular switches with applications where stimuli-responsive materials are required.