Single-molecule spectroscopy studies of molecular dynamics in chemical and biological systems

Single-molecule chemical kinetics of interfacial electron transfer from excited cresyl violet molecules to the conduction band or energetically accessible surface electronic states of indium-tin-oxide (ITO) was studied under ambient conditions. We revealed that the physical origin of multiexponential kinetics of electron transfer in this system is the inhomogeneity of molecular interactions on the semiconductor surface of ITO. Spontaneous and photo-induced spectral fluctuations of single sulforhodamine 101 molecules at the glass-polymer interface were investigated and attributed to transitions between metastable minima in the molecular potential-energy surface. Similar conformational fluctuations are also observed for the active site of the cholesterol oxidase, flavin adenine dinucleotide (FAD), which results in dynamic disorder in the enzymatic reaction of cholesterol oxidase.