Dissertation Information
Title: Photophysical Studies of DNA-templated Molecular Dye Aggregates
Program: Doctor of Philosophy in Materials Science and Engineering
Advisor: Dr. Bill Knowlton, Materials Science and Engineering
Committee Members: Dr. Bernard Yurke (Co-Chair), Materials Science and Engineering; Dr. Ryan Pensack, Materials Science and Engineering; Dr. Daniel Turner, Materials Science and Engineering; and Dr. Joseph Melinger, Materials Science and Engineering
Abstract
Closely-spaced supramolecular assemblies of dye molecules, known as dye aggregates, experience coherent electronic interactions that can drastically alter their optical properties with respect to the isolated dye. These coherent interactions can cause changes to the optical properties such as shifts in optical absorption and emission spectra, as well as modulation of absorption and fluorescence intensity. Dye aggregates are therefore of interest for applications in organic optoelectronics, sensing, and nanoscale computing. In addition, coherently delocalized excited states, known as molecular excitons, are an emergent property of dye aggregates that are of interest for quantum information applications and quantum computing. However, these properties of dye aggregates have historically been difficult to control, owing to their sensitivity to the mutual orientation and separation of the dyes that comprise them. In recent years, DNA nanotechnology has provided researchers with significantly enhanced control of dye aggregate assembly. Specifically, it is possible to use DNA scaffolds to spatially position dyes with up to sub-nanometer resolution with strict control over the number of dyes comprising an aggregate.
This talk will highlight selected results from three photophysical studies of cyanine dye aggregates assembled on DNA, which were aimed at better understanding the relationships between structure, optical properties, and excited-state dynamics of DNA-templated dye aggregates. In the first study, we examine DNA-templated heteroaggregate tetramers of the cyanine dyes Cy5 and Cy5.5, which exhibit composition-dependent shifts in their optical absorption frequencies that are reminiscent of alloying. In the second study, we show that aggregation leads to an increase in nonradiative relaxation that drastically decreases the excited-state lifetimes of DNA-templated dimers and tetramers of Cy5 relative to the monomer. In the third study, we demonstrate how spectroscopic and analytical techniques can be used to identify and characterize subpopulations in DNA-templated dye aggregates.