Polarized fluorescence spectroscopy of two-ground- and two-excited-state systems in solutions

The polarized fluorescence spectroscopy of two-ground and two-excited state systems in solution is discussed. A state-dependent diffusion model for the rotational motion of an asymmetric, symmetric and spherical rotor is considered. Analytic expressions for the polarized fluorescence components in the case of symmetric and spherical diffusors are derived. The absorption and emission transition dipole moments have different directions in the molecule-fixed frames in both ground-and excited-state species. The case of double absorption bands with different directions of absorption dipole moments, in both ground-states species, is discussed. The problem of convolution between the instrument response function with a model decay is also discussed. Two methods for recovering the instrument response function are considered; namely, the scatter method and the method of a monoexponential reference compound. The theory discussed in this work can be employed to many problems important from an experimental point of view e.g., different kinds of excited-state reactions or excitation energy transfer in rigid double-chromophore complexes. Computer generated synthetic decays of polarized fluorescence and emission anisotropy for the one-ground- and two-excited-state problem are exemplified.