Date Awarded

2021

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Chemistry

Advisor

Kristin L Wustholz

Committee Member

Nathan M Kidwell

Committee Member

William R McNamara

Abstract

Growing global energy demands have necessitated the search for alternative sources of renewable fuels. Dye-sensitized photocatalysis (DSP) is a promising low cost, sustainable method that directly converts solar energy to readily usable forms of energy such as hydrogen fuel. While DSP is a promising technology, its efficiency is limited by back electron transfer and kinetic redundancy. In order to fully understand these processes, single-molecule spectroscopy (SMS) is used to probe the electron transfer (ET) dynamics of photosensitizers. In particular, eosin Y (EY), a brominated fluorescein derivative that undergoes intersystem crossing prior to injection, is investigated using SMS. In this approach, blinking dynamics - stochastic fluctuations in emissive and nonemissive intensities under continuous photoexcitation - are measured for single molecules of EY on glass, TiO2, and in oxic and anoxic environments. The emission dynamics are parsed into emissive (“on”) and nonemissive (“off”) events and fit to cumulative probability distributions using a maximum likelihood estimation and Kolmogorov-Smirnov test approach. In the absence of TiO2, the data are lognormally distributed, consistent with triplet state decay and dispersive electron transfer. However, for EY-sensitized TiO2, the on- and off-time distributions are not well described by any tested functional form, motivating us to implement new modeling approaches (e.g., finite mixture model, Monte Carlo simulations). Our results show that back-to-back events, temporal binning, and thresholding obscure the functional form and are thus important considerations for understanding the underlying ET dynamics.

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