Abstract:
Optically excited-states that result in localized, bound electron-hole pairs or excitons are central to many optoelectronic and photonic technologies. To develop such technologies, it is necessary to understand and control the energy, nature, and dynamics of the exciton. In this talk, I will present on our recent studies aimed at understanding the nature and dynamics of localized excitons in nanostructured materials using first-principles computation. 
For sp3-doped single-walled carbon nanotubes (SWCNTs), a promising class of optoelectronic materials with bright tunable photoluminescence and demonstrated single-photon emission, we characterize exciton trapping due to the presence of the defect. For nitrophenyl-doped (6,5) SWCNT, both experiment and theory indicate a long-lived spin is introduced via the defect. By comparison of theory and experiment, we predict that the exciton associated with the observed single-photon emission is a valence to conduction type excitation red-shifted due to defect-induced symmetry breaking and the presence of the defect-induced in-gap state. Additionally, we predict an asymmetry between the contribution of the two spin channels, suggesting this system has potential for spin-selective optical transitions. We then suggest new atomic-like dopants that display similar excitonic properties but possess increased spin-orbit coupling and have a potential for greater synthetic control. 
Next, I will present studies of exciton dynamics in stacks of functionalized PTCDI DNA base surrogates as a model system to study exciton delocalization and dynamics within ordered organic assemblies. We determine that the intra- and inter-molecular interactions result in distinct vibrational, electronic, and optical properties. Furthermore, we show that stacking of molecules increases the efficiency of non-radiative relaxation dynamics from a high excitonic state to the lowest energy exciton. Overall, these studies demonstrate that excitonic properties can be modified via inter-molecular electronic and vibrational interactions.

Bio:
Dr. Sahar Sharifzadeh is an Associate Professor at Boston University. She obtained her PhD from Princeton University, working under the guidance of Prof. Emily Carter, and subsequently joined the Molecular Foundry at Lawrence Berkeley National Laboratory as a postdoctoral fellow and project scientist in the group of Dr. Jeffrey Neaton. She joined Boston University in 2014 as an Assistant Professor. Her research focuses on understanding the electronic structure of materials from first-principles theory with a focus on excitonic properties.

In-Person Location:  Bldg. 440, A105/A106

Virtual Link: https://argonne.zoomgov.com/j/1600052763