Fast colorimetric screening for visible light photocatalytic oxidation and reduction reactions

Abstract

Fast screening accelerates the discovery and optimization of chemical reactions. Here, we present the parallel irradiation and evaluation of 96 visible light photocatalytic reactions in a microtiter plate. After completion, a chemical indicator is added, allowing the spectroscopic determination of the formed stoichiometric by-products. Their quantity correlates in many cases with the conversion of starting materials and yield of photochemical reaction products. We demonstrate the concept with known photooxidations of organic compounds by riboflavin tetraacetate (RFTA) and reproduce published results and gas chromatographic analyses by a colorimetric assay. Two new photocatalysts for the hydroxylation of boronic acids and new substrates for the photocatalytic generation of aryl radicals from aryl halides were identified. By screening a series of drug molecules containing aryl halides, new photochemical dehalogenation reactions were found. The presented methods enable laboratories lacking sophisticated high-throughput analytical instrumentation to perform parallel optimization and scope determination of photocatalytic oxidation and reduction reactions.