Fluorescence excitation spectra of single perylene molecules embedded
in the Shpol'skii matrix n-nonane have been investigated at 1.7 K. On
a time scale which is considerably larger than the tripler lifetime of
the molecule, discrete spectral jumps of the single molecular absorpt
ion lines are observed. To investigate this jump behaviour, fluorescen
ce excitation spectra at different applied electric field strengths to
the sample have been recorded. From the resulting Stark shifts and th
e spectral jumps a maximum distance between the molecules and disturbi
ng two-level systems can be estimated.