Tuning the pH of Activation of Fluorinated Hydrazone-Based Switches─A Pathway to Versatile 19F Magnetic Resonance Imaging Contrast Agents

Abstract

Molecular switches have become an area of great interest in recent years. They are explored as high-density data storage and organic diodes in molecular electronics as well as chemosensors due to their ability to undergo a transition between well-defined structures under the action of external stimuli. One of the types of such switches is hydrazones. They work by changing the configuration from E to Z under the influence of pH or light. The change in configuration is accompanied by a change in the absorption band and changes in the nuclear magnetic resonance (NMR) spectrum. In this publication, the structure-property relationship of fluorinated hydrazone switches was established. A linear relationship between the Hammett substituent constants and the pH where the switching occurs was found. Introduction of strong electron-donating groups allowed obtaining a hydrazone switch of pKa = 6 suitable for application in 19F MRI as contrast agents.