Exploring Charge-Transfer Properties of Donor-Acceptor Functionalized Squaraine Dyes

Date

2023-08-28

Authors

Stanley, Austin

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Abstract

In the realm of optoelectronics and solar technology, the demand for efficient and cost-effective materials has intensified. Squaraine dyes have emerged as a promising class of compounds for these applications, owing to their ability to absorb light and facilitate charge transport across different layers within materials. This thesis aims to present the synthesis and characterization of a novel donor-acceptor (DA) functionalized squaraine dye, featuring redox-active phenols that can be oxidized to phenoxyl radicals. Our objective is to investigate the charge-transfer (CT) properties of these compounds using spectroscopic techniques and computational modeling. Chapter 1 provides an introduction to organic DA compounds, the probing of intramolecular charge-transfer (ICT) in such systems, and a background on stable free radicals and squaraine dyes. The chapter sets the context for the application of these molecules in materials and outlines the goals of the thesis. Chapter 2 focuses on the synthetic methodology and nuclear magnetic resonance (NMR) spectroscopic characterization of a series of previously unreported DA compounds and squaraine dyes. The synthesis of compounds 2.14 and 2.15 is described using Suzuki-Miyaura chemistry, followed by the coupling of 2.14 to a known squaraine dye via Suzuki-Miyaura cross-coupling to form 2.25. The synthesis and NMR characterization of these compounds are presented, along with the proposal of a structural motif (2.31) and the discussion of attempts to synthesize it. Preliminary data supporting oxidative addition to form 2.30 are also provided. Chapter 3 focuses on the photophysical and redox properties of compounds 2.14, 2.15, and 2.25. UV-Visible and fluorescence spectrophotometry techniques are employed to demonstrate the CT characteristics of each compound. Cyclic voltammetry is used to investigate the oxidation potentials of the phenols in 2.14 and 2.25, while the attempt to isolate stable free radicals is discussed. Computational data using density functional theory (DFT) and time-dependent DFT (TD-DFT) are used to support the experimental findings, including the plotting of frontier molecular orbitals (FMOs) and natural transition orbitals (NTOs). Chapter 4 provides a comprehensive summary of the results presented in this thesis and suggests future experiments for further investigation. Additionally, preliminary computational results for compound 2.31 are briefly discussed. In conclusion, this thesis explores the CT properties of novel compounds, particularly focusing on the influence of donor character on the photophysical properties. This research contributes to the understanding and potential applications of DA functionalized squaraines in optoelectronics and solar technology.

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Keywords

Squaraine, squaraine dye, Chemistry, Organic Chemistry, dye chemistry, materials chemistry

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