Novel Sensitizers and Chromophore-catalyst Assemblies for Photocatalysis
A fundamental understanding of the photophysical processes of charge transfer and energy transfer on the nanoscale is critical for the development of a wide array of applications including catalysis, biosensing, optoelectronics, and green-energy solutions. Recently, interest has shifted towards organic materials, as they provide for simpler processability, lower production costs, and minimized environmental impact in comparison to inorganic counterparts. In the work described here, the photophysical properties of several pi-conjugated organic materials are investigated with the aim of identifying their viable applicabilities. First, a series of diimide-functionalized rylene dye derivatives in their 1-electron reduced form were analyzed by ultrafast transient absorption spectroscopy. Excited-state lifetimes of these anions were measured in the presence of aryl quenchers that exhibit a range of reduction potentials. In this way, Stern-Volmer analysis was used to determine if the excited-state anion could be used as a catalyst for the reduction of aryl halides. It was concluded that, with decreasing the size of the rylene core, the excited state anion acts as a more potent reducing agent. Second, a Ru-based chromophore-catalyst assembly was designed and analyzed for its viability in CO2 reduction. Analysis by gas chromatography found that this material can be used for artificial photosynthesis. Lastly, the Stern-Volmer quenching behavior of water-soluble poly(phenylene ethynylene) derivatives was investigated by fluorescence spectroscopy. An amplified quenching effect was found when Au nanoparticles were used as quenchers, exhibiting KSV as high as 1012 M-1 for particular nanoparticle shapes and sizes. This shows promising applicability to sensing applications.