The influence of morphology on excitons in single conjugated molecules

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Title The influence of morphology on excitons in single conjugated molecules
Publication Type dissertation
School or College College of Science
Department Physics & Astronomy
Author Thiessen, Alexander
Date 2014-12
Description The electronic properties of π-conjugated molecules are strongly related to their molecular shape and morphology of assembly in three-dimensional space. Understanding the various structure-property relationships is relevant to the applications of these materials in optoelectronic devices such as organic light-emitting diodes, field effect transistors and photovoltaic cells. The fact that conjugated systems interact with visible light opens these materials to a plethora of noninvasive spectroscopic investigation techniques. In this work, electronic properties of different π-conjugated systems are studied spectroscopically on the ensemble and the single molecule levels. Single molecule spectroscopy is advantageous in that it allows the investigation of the individual nuclear building blocks that contribute to the properties of the ensemble. Additionally, transient photoluminescence spectroscopy methods can provide useful insight into the temporal evolution of the emissive states. In combination with these methods, novel π-conjugated model molecules are used to probe processes related to exciton dynamics. For the first time, the spatial localization of excited states is probed experimentally in a molecule with a circular chromophoric structure. In addition, a set of model molecules with different geometries is employed to study exciton relaxation in π-conjugated systems. The molecular morphology is utilized to distinguish between processes such as nuclear reorganization and torsional relaxation. Furthermore, single molecule spectroscopy is used to study the electronic structure of individual polymer chains in the photovoltaic cell material poly-(3-hexylthiophene). Optical spectra of this polymer are known to change with the morphology of the bulk film. Single molecule studies reveal that individual polymer chains exhibit similar behavior and indicate that spectral diversity is an intrinsic property of single P3HT molecules. The main results of this work are the following: (1) Excitations in a molecule with rigid circular geometry are shown to localize randomly between different parts of the molecule and show no correlation with the orientation of the excitation light polarization. (2) Model systems can be used to differentiate between different dynamics of exciton relaxation and, furthermore, processes such as torsional relaxation can be inhibited by a rigid molecular structure. (3) The electronic structure of single P3HT molecules is strongly dependent on polymer chain conformation and can be influenced by the surrounding host polymer.
Type Text
Publisher University of Utah
Subject Conformational disorder; Exciton localization; Photophysics; Pi-conjugated systems; Single-molecule spectroscopy; Structure-property relations
Dissertation Institution University of Utah
Dissertation Name Doctor of Philosophy
Language eng
Rights Management Copyright © Alexander Thiessen 2014
Format application/pdf
Format Medium application/pdf
Format Extent 3,287,944 bytes
Identifier etd3/id/3305
ARK ark:/87278/s6pv9tn6
Setname ir_etd
ID 196870
Reference URL https://collections.lib.utah.edu/ark:/87278/s6pv9tn6
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