Dynamics of fluorescence of a dye molecule in solution

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Abstract
Transient and stationary fluorescence properties of rhodamine 6G in liquid ethanol have been investigated in a wide temperature range between 110 and 300 K. Various phenomena concerning the interaction between the dye molecule and the surroundings such as dynamic Stokes shift, stepwise temperature dependence of the fluorescence peak energy, and excitation-wavelength dependent fluorescence peak shift, have been observed. To explain these phenomena in a unified manner, a stochastic theory based on the Onsager cavity model has been developed. It is shown that the fluorescence as well as the absorption characteristics are explained well by this treatment. Various parameters characterizing the optical properties of the molecule, i.e., the dipole moments in the ground and excited states, transition energy in vacuum, temperature-dependent relaxation time of the dynamic Stokes shift and so on, can be derived from the comparison between the theory and experiment. Finally, the origin of the relaxation processes found in the present work is discussed in connection with the dielectric properties of the solvent and also with the resonance Raman scattering process.