The utility of a Lewis acid is dependent on its effective strength in solution.  The simple definition of Lewis acidity affords a vast array of Lewis acids which complicates universal measurement. We have developed a new method for measuring Lewis acid strength based on the measure of fluorescent Lewis acid/base adducts.  We utilize chromaticity measurements of fluorescent adducts and avoid comparison of the Lewis acids to a sole Lewis base.  By measuring the acidity of the active species in solution the FLA method provides more utilitarian measures than common computational method.  By nature of using chromaticity, and the definition of our scale we afford more precision and versatility than other spectroscopic methodologies.  We currently have catalogued a wide variety of over 50 Lewis acids on one scale, including boranes, silanes, heavy group 13 acids, transition metal species, and even cationic Lewis acids.  We are even able to explore the influence of solvent on Lewis acid strength and probe the catalytic potential of a specific Lewis acid.  The FLA method will be presented including a brief summary of the versatility of the measure, as well as some known pitfalls, and finally an introduction into our ability to observe solvation effects on Lewis acidity.

The FLA (fluorescent Lewis adduct) method: Shining light onto Lewis acidity

ACS Fall 2021

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