Surface Preparation for Single-Molecule Chemistry.

Immobilization procedures, intended to enable prolonged observation of single molecules by fluorescence microscopy, may generate heterogeneous microenvironments, thus inducing heterogeneity in the molecular behavior. On that account, we propose a straightforward surface preparation procedure for studying chemical reactions on the single-molecule level. Sensor fluorophores were developed, which exhibit dual-emissive characteristics in a homogeneously catalyzed showcase reaction. These molecules undergo a shift of fluorescence wavelength of about 100 nm upon Pd(0)-induced deallylation in the Tsuji-Trost reaction, allowing for separate visualization of the starting material and product. Whereas a simultaneous immobilization of dye and inert silane leads to strongly polydisperse reaction kinetics, a consecutive immobilization routine with deposition of dye molecules as the last step provides substrates underlying the kinetics of ensemble experiments. Also, the found kinetics are unaffected by the chemical variation of inert silanes, nearly uniform, and therefore well reproducible. Additional parameters like photostability, signal-to-noise ratio, dye-molecule density, and spatial distribution of dye molecules are, as well, hardly affected by surface modification in the successive immobilization scheme.