NMP 2008

	Julia Rossini
	ADVISOR: Wayne Gladfelter Chemistry Department University of Minnesota

Synthesis of Excited-State-Donor/Acceptor Dyads Containing Transition Metal-Based Dyes and Zinc Oxide Nanoparticles

To better understand the specific charge transfer events that occur within a dye-sensitized solar cell (DSSC), we are synthesizing well-defined excited-state-donor/acceptor dyads. A transition metal-based dye containing customized polypyridyl ligands will serve as the excited-state donor to an electron-accepting zinc oxide nanoparticle. ZnO is a promising semiconductor for DSSCs due to its 3.37 eV band gap and its ease of solution processing to yield a variety of morphologies. Different routes to ZnO nanoparticles have been explored. A route used in many publications involves the precipitation of the nanoparticles from zinc acetate and a hydroxide source in ethanol. Particle sizes ranged from 2-5 nm as measured by their absorption onset in UV-Vis measurements however the lack of long-term stability for these dispersions led to the exploration of other preparation procedures. Using a modification of the process developed by Chaudret, et al. ZnO nanoparticles ranging in size from 3-5 nm were synthesized from the molecular precursor bis(diisobutylamido) zinc and were capped with n-hexylamine to prevent particle agglomeration. We expect to attach the dye directly to the nanoparticle through substitution with the n-hexylamine capping agent as represented below. Once attached, we will look at the quenching ability of the dye on the fluorescence spectrum of the ZnO nanoparticles to explore charge injection. The electronic properties of the dyad will be controlled by adjusting the size of the nanoparticle, varying the length of the linking substituent on the dye as well as altering the structures of the ancillary polypyridine ligands. The reduction potential of the dye can be tuned by systematically altering any electron donating or electron withdrawing substituents on the subsidiary bipyridine ligands.