Freezing and glass transition phenomena for 1,2-dichloroethane under high pressure as revealed by fluorescence spectroscopy

Abstract

The viscosity of 1,2-dichloroethane increases steadily with increasing pressure, as does the density, refractive index and polarizability of this solvent. The pressure dependence for each of these properties can be monitored by a combination of absorption and fluorescence spectroscopy carried out in the presence of a fluorescent molecular rotor that responds to changes in the local environment. At 20 °C, dichloroethane freezes under an applied pressure of ca. 370 MPa, causing sudden extinction of the fluorescence of the molecular rotor due to the opaque nature of the frozen solvent. However, this same emission is enhanced dramatically if a small amount of inert polymer is present in the solution. The behaviour is interpreted in terms of the polymeric solute promoting establishment of a glassy matrix with reasonably good optical transparency for emission spectroscopy.