Investigations of redox-active dithiafulvenyl-substituted polycyclic aromatic hydrocarbon systems: DFT and TD-DFT studies

Eradeh, Ramin (2023) Investigations of redox-active dithiafulvenyl-substituted polycyclic aromatic hydrocarbon systems: DFT and TD-DFT studies. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This PhD thesis demonstrates the design, implementation, and applications of the redox-active 1,4-dithiafulvene and its arene-substituted derivatives. The research is mainly based on computational modeling and simulations, employing techniques such as density functional theory (DFT), time-dependent density functional theory (TDDFT), molecular dynamics (MD), and other quantum mechanical methods. These investigations include a broad range of fundamental properties, including attractive and repulsive non-covalent interactions between redox-active 1,4-dithiafulvenes and their reaction mechanisms associated with such interactions. Additionally, the UV-vis and fluorescence behaviors of a modified self-condensed pyrene-4,5-dione product has been studied through a combined approach of experimental and theoretical analyses. The results of this thesis disclose the fundamental mechanisms and intermolecular interactions that underpin the behaviors of the above mentioned compounds. Experimentally, 1,4-dithiafulvene (DTF) derivatives have been found to reduce Au (III) species in organic media to yield gold nanoparticles (AuNPs). This reaction provides a promising method for the synthesis of AuNPs, however, theoretical investigations into the surface thermodynamic properties of AuNPs, interactions between DTF and Au clusters, and solvent effects were lacking. In the first project of this thesis, systematic computational studies were carried out to gain in-depth understanding of the bind mechanisms of DTF radical cations and AuNP surface. DFT analysis indicated that sulfur and oxygen atoms in the DTF moiety serve as primary binding sites, while TD-DFT calculations predicted electronic transition bands agreeing with the experimental UV-Vis absorption spectra of AuNP/DTF complexes. The results in this work provide valuable guidance for controlled AuNP synthesis and functionality engineering. In the second project, the oxidative dimerization mechanism for a phenylsubstituted 1,4-dithiafulvene (Ph-DTF) was examined by DFT calculations. Detailed thermodynamic and kinetic properties of the various possible reaction pathways were obtained. The effects of electron-withdrawing and electron-donating substitutions as well as organic solvents on the dimerization reactivity was also studied. The computational results showed that these effects play critical roles in the dimerization mechanism, which deepen the understanding of the dimerization mechanism for various arene-substituted DTF molecules. The third project of this thesis focuses on a series of arene-substituted dithiafulvene (Ar-DTF) compounds, investigating their molecular structures and electronic properties. A correlation emerges between the π-system size and radical cation stability upon oxidation, driven by increased π-delocalization. Exceptions to this trend emphasize the role of molecular geometry. Charge transfer phenomena highlight efficient electron-hole distribution with larger π-systems, offering design principles for tailoring electronic properties. In the fourth and last study, a π-conjugated compound obtained from a selfcondensation reaction of pyrene-4,5-dione was characterized. Its excimeric emissions were investigated in various organic solvents to show significant solvatochromic effects. Host-guest complexes with cyclodextrins illustrate potential applications in chemical sensing and optoelectronics. X-ray crystallography, TD-DFT, and conformer calculations deepen the understanding of its molecular structure and excimer formation. Overall, this thesis presents a multi-dimensional perspective on DTF and its π- conjugated derivatives, elucidating their behavior and potential applications. The insights gained from these studies pave a way for future research endeavors, inspiring the development of innovative materials and technologies across diverse scientific and technological domains.

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