Pressure shift and solvent shift: A hole-burning study of resorufin-doped glasses

We use pressure-tuning hole-burning spectroscopy to investigate the ionic dye resorufin in glycerol and ethylene glycol/water glass. By varying the burn frequency over the inhomogeneous band, we found a well-defined frequency where the pressure-induced line shift changes its sign. This frequency is characterized by strong compensation effects between blue- and red-shifting molecular forces. In some systems there can be several such frequencies with vanishing pressure shift due to different modifications of the probe in solution. These findings are interpreted in terms of microscopic disorder as expressed through the two-particle density correlation and a competition between dispersive and electrostatic interactions.