Lewis acids coordinate to the phosphoryl group of the dithienophosphole, leading to a red shift in fluorescence emission. Correlation of the chromaticity data of the resulting fluorescent Lewis acid-base adducts (FLAs) with a dithienophosphole of normalized base strength allows for effective and reliable quantification of the strengths of a wide range of important Lewis acids.

Experimentally determining the strength of a Lewis acid is a highly desirable and important task that has implications across the chemical sciences. Recently, we developed a new fluorescence-based method for evaluating the relative acidity of a small series of Lewis acids across the p- and d-blocks of the periodic table with great precision against a series of Lewis basic fluorescent dithienophosphole oxide probes. In this report, we considerably expand the scope of the fluorescent Lewis adduct method by systematically investigating the apparent acidities of more than 50 Lewis acids in toluene. Notably, a number of the investigated Lewis acids have never been experimentally measured before. Our refined guide, which now also alleviates the uncertainties that we identified with our original method, is simple and reliable. It shows extreme sensitivity to small structural or electronic perturbations and can account for coordinative flexibility or aggregation events that occur in solution, providing an alternative method for Lewis acidity determination that is complementary to the established nuclear magnetic resonance-based methods.

Reaction of dithienophospholes with quinones provides hypervalent phosphorus species with square-pyramidal geometry and promising reactivity.

Two strongly electron-accepting viologens, including an intriguing tricationic species, are reported. The utility of the tricationic viologen for energy storage has been showcased via use as electrode in a proof-of-concept battery.