Energy transfer and formation processes in cylindrical J-aggregates



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Understanding light harvesting systems such as plants and bacteria that use photosynthesis to transport sun light energy to a photosynthetic reaction center is integral to creating efficient, man-made light harvesting devices. One such system is supramolecular aggregates made from the amphiphillic carbocyanine dye 3,3’-bis- (2-sulfopropyl)-5,5’,6,6’-tetrachloro-1,1’- dioctylbenzimida-carbocyanine (C8S3) which self assembles in aqueous solutions into double- nanotubes comparable to the (antennae) found in the photosynthesizing green sulfur bacteria (GSB). This research uses thin film confocal microscopy and bulk spectroscopy to elucidate the nature of energy transport and formation of groups of C8S3 nanotubes and groups of these nanotubes known as bundles. Confocal microscopy is used to determine energy transport distances of C8S3 nanotubes and bundles in air. The nanotubes were found to have transport distances of ~150 nm whereas the bundles were found to have transport distances of over 500 nm prompting further research into the bundles and their formation. Nanotube solutions with salt added were studied as they evolved into bundles to determine if salt could increase the rate of bundle formation. Linear dichroism, AFM and bulk spectroscopy were used to track the process of nanotubes to bundles and a fitting scheme was created to quantify the rate of bundle formation. The energy transport distance of bundles was further tested by first forming a scheme to disperse the bundles in a polymer matrix without altering their form and then imaging the bundles in the polymer matrix using confocal microscopy. Energy transport distances were calculated to be ~10 nm rather than the longer distances in air. Temperature dependent studies were completed to determine how to effectively retain the structure of the nanotubes and bundles while at temperatures <77K. This information can be used to attempt low temperature confocal microscopy to further understand this complex system.