Investigation of probe–solvent interactions: color effects in optical line widths

We have measured the optical hole width as a function of wave number across the inhomogeneous lines for two aromatic probe molecules, namely thionin and BODIPY. Upon tuning the laser to the red edge of the inhomogeneous band the hole width of thionin decreases, whereas the hole width of BODIPY increases. The color effect is correlated with the solvent shift in the former case and anti-correlated in the latter case. We suggest possible scenarios to explain these observations and back up our reasoning by site dependent Stark-effect experiments.