Industrial electrochemical processes have been growing in importance for decades. However, with the need for improved efficiency in these processes comes the need for better fundamental understanding. For example, improved battery performance requires accessible, more precise metrology to aid in their development. Many attempts at the fabrication of fluorescent probes adaptable to these systems have produced differing levels of success. Typically, one of the three major requirements (broad electrochemical stability, reversible behavior, and efficient kinetics) are missing. In addition, most probes do not allow the study of single electron processes, but instead require from 2 to 6 electron transfer processes and are susceptible to side reactions. This invention addresses all of the above issues. In addition, the probe has a high quantum yield, which means very small quantities are needed. Coupled with a simple one pot synthesis and the above attributes, this makes Ferrocene-Bodipy a unique and very desirable electrochemical probe molecule.
The invention is a pro-fluorescent molecule that responds reversibly in oxidation/reduction conditions. This in itself is not unique. The uniqueness is in the mechanism of oxidation/reduction and its molecular design. Towards the molecular design, the fluorescent center was chosen to be 2,8-die thyl-5 ,5-difluoro-1,3,7,9,10-pentamethyl-5H -4A4 ,5A4 - dipyrrolo[l ,2-c:2',l '-j][l ,3,2fdiazaborinine (Bodipy). The Bodipy family of dyes is known for their high quantum yield, chemical stability and lack of toxicity. The moiety (ferrocene) in the meso position of the fluorescent center can undergo oxidation and reduction reversibly through a single electron transfer route. In the ferrocenium state (Fe III), the molecule is not fluorescent. Upon addition of one electron through reduction, the ferrocenium becomes ferrocene. This significantly reduces the electron withdrawing characteristics of this functional group and the fluorescent center becomes active. This yields a spectroscopically active sensor that can report on redox kinetics in electrochemical devices such as: batteries, fuel cells, or in industrial electrochemical processes. This will provide an orthogonal pathway to characterize and assay these systems. In addition, the probe can function as an early warning detection system for device failure due to loss of electrode efficiency or growth of electrolyte dendrites if coupled with optical systems.
The current practice requires excessive testing and imaging by electron microscopy (for solid state batteries), which are expensive and time consuming. Introduction of this molecule will give a highly sensitive metric in both voltammetry and fluorescence spectroscopy to report efficiency and stability of a given device. The molecule can be introduced to a solid electrolyte during processing or included in an electrolyte solution in nanoscale concentrations to observe spectrophotometrically.