FLUORESCENCE MICROSCOPY OF SINGLE MOLECULES

Using fluorescence excitation spectroscopy single pentacene molecules were studied under a microscope at a temperature of 1.8 K. The microsc ope has a resolution of 3 mu m and allows the location of a single emi tting molecule with an accuracy of 0.5 pm, in a total viewing field of 235 mu m 175 mu m. 133 images have been recorded by increasing the ex citation frequency of the light at 592.344 nm in steps of 2 MHz. Each single molecule has a Lorentzian absorption profile with a width of ab out 14 MHz and can be observed in 10 consecutive images. The ''positio n'' of the single molecule is characterized by the x- and y-coordinate s in the spatial domain and by its absorption frequency in the spectra l domain.