Date of Award
Doctor of Philosophy (PhD)
Mark G. Steinmetz
James R. Gardinier
Over the past decades, a variety of pi-conjugated organic materials have been explored as potential charge transport materials in conducting layers of photovoltaic devices. The performance of these devices critically depend on the efficiency with which the charge carriers (electrons and/or holes) move within the pi-conjugated materials present in their hole and electron conducting layers before their collection at the electrode. Hence, a large amount of research effort is devoted not only to the preparation of new pi-conjugated organic molecules for charge transport applications but also in understanding the nature of charge transport along the molecule (intra-chain) as well as between the molecules (through space or inter chain) when they are packed together in different orientations and varied extent of overlapping.
As a model mimicking the packing of organic chromophores with varying degree of overlap in conducting layers of photovoltaic devices, a series of alkyl substituted pyrenes with incrementing bulk around the pyrene chromophore was prepared. The structure-activity relationship was studied by evaluating the effect of introducing the sterics on pyrene core upon pi-pi stacking as observed in monomer/excimer emission as well as that of binding ability of cation radical with its neutral counterpart to form a dimeric cation radical. The electronic and steric influence of aryl groups on the pyrene core was evaluated by preparing a series of tetraaryl substituted pyrenes. A series of nanometer size tetraarylethylenes with increasing emission quantum yields was also prepared and the optoelectronic properties were studied. Using 9-position of fluorene backbone for the attachment of solubilizing groups; 2,7-position for the Suzuki coupling reaction; and 3,6-position for Scholl reaction, a number of new emissive chromophores including doubly annulated fluorenes, helicenes and molecular hubs for the construction of dendrimeric structures were also prepared and the optoelectronic properties were studied.