Photophysical Characterization of Small Organic Molecules Via Time-Resolved and Steady-State Spectroscopic Techniques

This dissertation describes in detail the photophysical characterization of novel organic dyes in the infrared region for bioimaging purposes in a rapidly evolving field which originates from the need for more efficient and bright systems that are capable of replacing current commercial options and functioning in biologically relevant media. Biological tissue, whether it be muscle, adipose, or epithelium, has a higher scattering efficiency, greater light attenuation, and stronger autofluorescence at shorter wavelengths, thus limiting the biological window to longer wavelengths. The goal of this dissertation was the comparison of novel organic dyes for commercial development as bioimaging dye candidates with unique combinations of donor, acceptor, and protecting groups, which is dependent on precise quantification of emission efficiency in environments with various polarities, viscosities, and temperatures. To accomplish this research, the quantification of steady-state and time-resolved spectroscopy of newly-developed near-infrared (NIR) emissive dyes in a variety of environments. By comparing their radiative characteristics to the current commercial forerunners in indocyanine green (ICG) and pafolacianine (Cytalux™), the only dyes approved by the Food and Drug Administration (FDA) for use in humans as bioimaging agents in the NIR, a more informed decision regarding further clinical development can be made. This work reveals that solvent selection has a direct and pronounced effect on the energetics, probabilities, and kinetics of the radiative transitions with two systems of unique ionic liquid and dye combinations possessing a molecular brightness an order of magnitude higher than ICG