Approaching Aromatic Interactions with Small Molecule Model Systems: Assessing N-Heteroarene in ∏ -Stacking and CH-∏ Interactions, Crystal Engineering of Atropisomeric Rotors, and Developing Responsive Organic Charge-Transfer Complex
Date of Award
Open Access Dissertation
Chemistry and Biochemistry
Ken D. Shimizu
Non-covalent interactions involving aromatic species are important in many areas in chemistry, biochemistry, and materials sciences. During the past two decades, small molecule model systems have emerged as a powerful tool to advance our knowledge of the stability trends for aromatic interactions in the condensed phase. Among these, the Cshape N-arylimide molecular balances developed by our laboratory have proven to be one most successful and versatile model systems that can be readily adapted to investigate various types of aromatic interactions. These molecular balances are particularly apt at isolating and accurately measuring the targeted weak aromatic interaction energies for different geometries. In this dissertation, our experimental efforts in utilizing the Narylimide molecular balance to examine the impacts of nitrogen-containing aromatic surfaces (N-heteroarenes) on π-stacking and CH-π interactions are detailed. Polar Nheteroarenes displayed pronounced electrostatic character in these interactions which influenced both their stability trends and geometric preferences. Introducing a formal positive charge at the heterocyclic nitrogen greatly enhanced these electrostatic effects. Next, this versatile molecular model system was applied to the study of the relationship between the solution and solid-state conformational preferences for rapid interconverting conformers. Close examination of a library of atropisomeric O-tolyl succinimide rotors revealed that the solution conformational preferences were generally excellent predictors of the conformational preferences in crystal structures. Interestingly, the correlation function between the solid-state and solution mole fraction of syn- conformer (χsyn) were not linear but fit to a step-function trend where the solid-state χsyn was either 0 or 1 for most rotors except for those with a solution χsyn of 0.50 ± 0.06. Finally, we examined the behavior of a dynamic intramolecular aromatic stacking donor-acceptor-donor complex. This system displayed interesting reversible color changes in the solid-state when treated with different organic solvents. The unique responsive behavior was attributed to solventinduced changes in the intramolecular stacking geometry of the D-A-D complex.
Li, P.(2015). Approaching Aromatic Interactions with Small Molecule Model Systems: Assessing N-Heteroarene in ∏ -Stacking and CH-∏ Interactions, Crystal Engineering of Atropisomeric Rotors, and Developing Responsive Organic Charge-Transfer Complex. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/3233