The electronic and spectroscopic properties of compounds containing aryl-aryl bonds are highly dependent on aryl-aryl torsional angles. Coplanar configurations of the arene subunits leads to more efficient pi orbital overlap resulting in enhanced conjugation of electrons, often leading to more efficient absorption and emission of light. Biphenyl and oligophenyl compounds capable of controllable and predicable input-driven torsional angle switching should be excellent candidates for molecular switches. Oligophenyl lactone-bridged systems, in the form of pi-expanded coumarins, have been synthesized and explored by us as reversibly cleavable aryl-aryl bridging units with pH as the stimulus. At high pH the lactone bridges are cleaved and at low pH the lactone bridges are re-formed, leading to a large and reversible change in dihedral angle of the aryl-aryl subunits. Both biphenyl and terphenyl lactones are capable of geometry switching with a measurable output of light absorption and emission modulation. Additionally, propeller-shaped pi-expanded coumarins have also been synthesized and will be studied as pH-driven molecular switches with the potential for reversible binding. One challenge of all of these types of molecules is that the planarity of these systems also leads to pi-stacking and aggregation resulting in problematic solubility and difficult characterization. We will present the synthesis of these molecules as well as successful strategies for solubilizing.<br/>

Pi-expanded coumarin crankshafts and propellers as aryl-aryl molecular geometry switches

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.