Three-State Donor-Acceptor Biaryl Lactone Molecular Switches with Enhanced Solubility

Abstract

Our research is focused on the synthesis of a bridged biphenyl molecule with an amino donor and tetraethylene glycol solubilizing groups (TEG). This three-state biphenyl molecule, due to its chemical properties, will find applications as nanoscale fluorescent sensors and molecular mechanical devices. Biphenyl molecules have known dihedral angles, leading to differing optical and conducting properties when manipulated. Utilizing a lactone-bridge, we can force the molecule into and out of planarity. At low pH, the molecule takes a planar conformation (“ON”), while at high pH it's non-planar (“OFF”). Previous research has shown similar two-state molecules’ effectiveness at readily switching conformations when exposed to different chemical environments. Prior research combined cyano and nitro acceptors with differing amino donors within biphenyl molecules to enhance optical properties and pH sensitivity. This pH sensitivity will be more precise with the addition of a third “OFF” state. At low pH, the amino group should become protonated, leading to the second “OFF” state and giving a narrow “ON” state. The “ON” state results in visible color differences from the “OFF” states of the molecule. These characteristics improve the usefulness of these molecules as pH sensors. Our research aims to synthesize a biphenyl molecule with a cyano acceptor, and TEGs. Prior research shows nitrile fluoresces better than its nitro counterpart. Long TEGs will increase the solubility of the molecule, enhancing the practicality of the planar biphenyl molecule as a dye. We have successfully synthesized one of our target molecules, a benzene ring with an iodine and a para-TEG group. We will be continuing our work to synthesize a three-state donor-acceptor biaryl lactone molecular switch with a cyano acceptor and TEGs, enhancing solubility and fluorescence.