  We report on time dependent Stokes shift measurements of single molecules.
Broadband excitation and emission spectroscopy were applied to study the
temporal Stokes shift evolution of single perylene diimide molecules (PDI)
embedded in a polymer matrix on the time scale of seconds. The Stokes shift
varied between individual molecules as well as for single molecules undergoing
different conformations and geometries. From the distribution and temporal
evolution of Stokes shifts, we unravel the interplay of nano-environment and
molecular conformation. We found that Stokes shift fluctuations are related to
simultaneous and unidirectional shifts of both emission and excitation spectra.
