Date of Award

Spring 2023

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

First Advisor

Linda S. Shimizu

Abstract

Porous organic crystals can be advantageous as nanoreactors and in sensing, separations, and storage. The Shimizu group utilizes bifurcated urea hydrogen bonding to direct the assembly small building block into pillars and columns affording functional porous crystals. Recently, our group has examined the incorporation of triphenylamines within the framework of bis-urea macrocycles. These macrocycles assemble into columns that contain the solvent of crystallization bound within the channels. Heating the crystals leads to removal of the solvent and activates the host for guest exchange by single-crystal-to-single[1]crystal transformations. Different electron accepting molecules can be encapsulated inside the pore of the host and trigger the host to guest electron/charge transfer. Depending on the reduction potential of the guest, the Gibbs-free energy required for the electron transfer changes. The molecule with higher reduction potential show photoinduced electron transfer upon UV irradiation. Moreover, encapsulation of the acceptors introduced lower band gaps in the host-guest complexes as compared to the free host 1 material, which may further lead to conductivity in the complexes. These robust porous crystals were also used to absorb monomers, including pyrrole (Py) and ethylenedioxythiophene (EDOT), which could be subsequently polymerized inside the host by heating in I2 atmosphere. 13C NMR, FT-IR, Raman and photophysical characterization shows presence of the polymers inside the channel. Chapter 1 provides an overview of the emergent properties of the urea tethered linear and macrocyclic TPA derivatives. Also, a brief introduction to the host[1]guest electron transfer, polymerization in confinement and organic radicals is provided comparing the literature examples. Chapter 2 focuses on the host-guest electron/charge transfer upon encapsulation of different electron accepting guests in the channels of TPA bis-urea host crystals. Chapter 3 examines the confinement effect of the host in polymerization reactions. Chapter 4 briefly focuses on how different crystallization condition can alter the assembly motif of the TPA bis-urea macrocycles. The TPA macrocycles assemble into planar conformation with dimethoxyethane encapsulated inside the pore. However, when dimethyl sulfoxide is bound in the channel, they adopt a bowl shape conformation. Single crystal structure revealed that both conformers assemble into columns through the urea-hydrogen bonding motif. The two crystal forms, with different guests display different amounts of photogenerated radicals. Further studies are currently in progress to understand the effect of the structural motif on the radical generation. Future directions are highlighted in Chapter 5. Overall, this work provides an avenue for the application of the TPA bis-urea macrocycles in electronic and conductive applications.

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Chemistry Commons

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