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    Modifying the self-assembled nanostructures of perylene bisimides in water and their applications

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    Perylene bisimide (PBI) performance in photovoltaic applications is highly dependent on their ability to form photogenerated radicals. Their aggregation and self-assembled nanostructures can have a large impact on their ability to form the photoconductive radical. Currently, the literature has been primarily focused on changing their aggregation and self-assembled nanostructures in organic solvents. However, there is a desire to move away from organic solvents and towards water as it is more environmentally friendly. The addition of pH sensitive groups onto the PBI chemical structure allows for them to be solubilised in water. This also allows for their aggregation and self-assembled nanostructures to be tailored through pH change. First, this work looked at how the counterion used to make the basic solution which solubilises the PBI could be used to change the aggregates and molecular packing in solution. This is a simple method and less time consuming compared to changing the PBI chemical structure to form new structures. The different metal ions used to form the PBI aggregates had different pH sensitivities and showed different nanostructures forming over a range of pHs. This also led to a change in the gelation kinetics for pH-triggered hydrogels and a difference in the bulk rheological properties. The solutions of PBI solubilised with different counterions at pH 6 were used to fabricate multilayer photovoltaic devices which showed varying degrees of power conversion efficiency depending on counterion choice. Next, the chemical structure was changed in the imide position with three similar amino acids. These PBIs were then characterised across various length scales to see how their self-assembled structures influenced their ability to form photoconductive radical at different pHs. This difference in molecular packing led to a difference in radical anion formation over a range of pHs. The difference in pH sensitivity led to a difference in the gelation kinetics when a pH trigger was used. It was also observed that the different pH sensitivities led to an increase in gel stiffness for one of the PBIs. Lastly the synthesis of three PBIs with different amino acid side chains that have been core-substituted with pyrrolidine groups were examined. The change in the functional group on the core is expected to change the π-π stacking. The addition of the electron density to the core leads to a dramatic change in the optical and redox properties. The PBIs were able to form radical cation instead of radical anion when irradiated. Their ability to self-assemble as pH was lowered showed that amino acid choice has a major impact on the nanostructures formed. They could be used to make pH-triggered hydrogels when the initial solution concentration was increased, however, these hydrogels could no longer form radical cation
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