Enhancing the Utility of Room Temperature, Catalyst-Free Dynamic Thia-Michael Acceptors Through Strategic Design

Although the catalyst-free dynamic thia-Michael reaction (tM) has been leveraged in a variety of significant applications ranging from material science and pharmaceutical development, exploiting its full potential has been limited by relatively low equilibrium constants (Keq). As such, a series of studies have been performed to explore structural changes to room temperature, catalyst-free tM acceptors with the intent of expanding the range of accessible equilibrium constants, as well as introducing light as a stimulus to alter equilibria. The first chapter of this thesis will serve as an introduction to dynamic thia-Michael reaction and its relation to my work. The second chapter will detail the development of the benzalisoxazolone (BIOx) tM acceptor, a cyclic analogue to its predecessor the benzalcyanoacetate acceptor, which displays a significantly expanded range of thiol-binding due to generation of aromaticity upon thiol addition. Incorporation into bulk films results in robust materials with a wide variety of thermomechanical properties based on the Keq, modulated through choice of electronic substitution, of ditopic acceptor used. The third chapter is a physical organic study into the effects on equilibrium constants of ortho-substitutions on the β-phenyl ring for all classes of room temperature dynamic. By utilizing the steric hindrance imposed by the ortho-substitution, out-of-plane twisting of the β-phenyl ring and α,β-unsaturated carbonyl of the free acceptor can be induced, resulting in destabilization of the free acceptor and an increase to Keq. The fourth chapter focuses on the development of BIOx tM acceptors with photo-controllable equilibrium constants. Using similar steric principles from chapter two, placing bulky substituents on the isoxazolone ring and photo-isomerizing from the Z to the less stable E isomer results in significantly increased equilibrium constants. These acceptors maintain their electronic tunability, and incorporation into organogels via ditopic acceptors results in gels that exhibit stiffening behavior upon excitation with light. The fifth and final chapter will outline some preliminary studies into materials utilizing tM acceptors with similar equilibrium constants but different kinetics.