Histons: New Quasi-particles and Time-Resolved Fluorescence Shift of Polar Disordered Media

With statistical thermodynamics methods, it is shown that the evolution of a polar luminescence probe + polar disordered medium system after pulse excitation is described by an equation for damped vibrations. From this it follows that in the solvation shell of the excited solute probe, not only synchronous librations but also cooperative jump reorientations of solvent molecules take place, and their damping motion is caused by localized dielectric friction. This collective molecular dynamics is examined as the motion of a quasi-particle called a histon. The histon moment of inertia and mass are determined. The concept of l- and j-histons are also introduced. In terms of this model the full correlation functions for nonequilibrium solvent dynamics are derived. The behavior of steady-state and time-resolved spectra is examined and it is found that the limiting short-wavelength position of the steady-state spectrum at a low temperature and that for time-dependent fluorescence at t 0 are not identical. The histon model has been used for interpretation of the emission band collapse that is observed in long-time evolution experiments. Some other problems of spectral broadening are also discussed. As predicted, sharp expansion of the fluorescence band takes place on an ultrafast time scale due to dephasing of l-histons.