Single molecule fluorescence for organocatalysis

Single-molecule fluorescence detection has a unique potential to observe rare events and has been proven useful for the investigation of catalytic reactions, e.g. with enzymes and zeolites. Applications in molecular chemistry, however, are still uncommon. In this thesis, the focus is on the study of organic reactions catalyzed by cinchona alkaloids. In order to monitor the reactions using fluorescence, catalysts and reagents carrying bright and photostable fluorophores were designed. For single molecule studies, reagents or catalysts are immobilized at surfaces of glass cover slips, allowing to observe single molecule events.
We mainly use total internal reflection fluorescence microscopy to study the mechanism of the Michael addition reaction catalyzed by cinchona alkaloid derivatives in heterogeneous conditions. We acquired the kinetics of hydrogen bonding between the bifunctional catalyst and a thiol and a maleimide and conclude that a model for the pre-reaction complex proposed by Wynberg is appropriate. Also, the rate constant for the formation of the product is determined from the intermediate state as ~10 s^-1 under our experimental conditions.
With single molecule fluorescence techniques, we also study the mechanism of the Biginelli multicomponent reaction catalyzed by acid and by chiral organocatalysts such as the cinchona alkaloids. In an attempt to determine the order in which the 3 reagents react, we designed two fluorescent probes, and applied them to track the reaction progress in homogeneous and heterogeneous conditions.
Additionally, as a part of an international project we investigated methods for the determination of photoluminescence quantum yields.