Date Thesis Awarded

4-2019

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Chemistry

Advisor

Kristin Wustholz

Committee Members

Nathan Kidwell

James Kaste

Abstract

Dye-sensitized photocatalysis (DSP) is a promising way to harvest solar energy for carbon-neutral fuel production, but a better understanding of how and why it is currently inefficient is necessary. This thesis will delve into the complex excited-state dynamics of Eosin Y (EY), a sensitizer for DSP, on glass substrates. By using single-molecule spectroscopy (SMS) to understand the underlying photophysics at play, we can gain a more complete understanding of the various photophysical events that contribute to inefficient DSP. In particular, SM blinking dynamics give insight into kinetic models.

SM blinking measurements of EY molecules in air and in N2 were separated into on- and off-time distributions and fit to heavy-tailed functions using the robust combined Maximum Likelihood Estimation (MLE) and Kolmogorov Statistic (KS) method. Both on-time distributions in air and N2 are power law distributed after an onset time. The off time distribution in air is best fit to a lognormal function, consistent with the Albery model for dispersive electron transfer. The off time distribution for N2, however, contained contributions from both an exponential and lognormal function with an onset time, consistent with a model where both intersystem crossing and dispersive electron transfer occur. The off-time distribution of an individual molecule was lognormally distributed, consistent with dispersive ET kinetics.

Additionally, blinking dynamics were investigated as a function of laser excitation power, revealing a power-dependence in the on times of individual EY molecules. Furthermore, preliminary studies of EY on TiO2 exhibit significant visual differences from blinking dynamics on glass. In future studies, the blinking dynamics and kinetics of EY on TiO2 will be explored in order to gain a more complete understanding of ET in technologically relevant conditions for the design and development of next-generation DSP solar cells.

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