Date of Award

Fall 2016

Document Type

Dissertation - Restricted

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Reid, Scott A.

Second Advisor

Dockendorff, Christopher

Third Advisor

Steinmetz, Mark

Fourth Advisor

Timerghazin, Qadir

Abstract

Formation of -stacked excimers plays an important role in many systems, ranging from biological phenomena and polymer formation and function to photovoltaic devices and organic molecular electronics. In these systems, the geometrical reorganization of the ground state upon photoexcitation is still a subject of debate. In this work, we compare the dynamics of excimer formation and hole (charge) stabilization in fluorene and fluorene-based model systems. We use a variety of gas-phase methods to examine the spectroscopy and dynamics of these systems, including Two-Color Resonant Two-Photon Ionization (2CR2PI), Hole-Burning (HB), Laser Induced Fluorescence (LIF), and Dispersed Fluorescence (DF). In order to quantify the clusters’ geometry, minimum, and relative energies, calculations using Density Functional Theory and high level ab initio methods are reported. These techniques were applied to better understand the energetic properties and behaviors of these model systems in their ground (S0), excited (S1), and ionized (M+•) states to probe the geometrical reorganization resulting in excimer formation and stabilization of charge. As model systems, we used fluorene based assemblies that are covalently linked by utilizing methylene or cyclohexane bridges, which connect two or more fluorene sub-units together. These are compared with clusters interacting at the van der Waals contact distance (3.5 Å). It was found that in both covalently linked and vdW bound systems, excimer formation is dominant; however, the excimer state is stabilized by covalent linkage. We also find cases in which the geometric requirements for excimer formation are not met. Almost every system studied displayed the ability to stabilize charge in its ionic state and therefore showed that the requirements necessary to delocalize charge are less stringent than those necessary for excimer formation.

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