Energy transfer between two mobile chromophores in a zero energy transfer configuration. Cross-correlation effects in the fluorescence anisotropy r(t)

摘要

The energy transfer process between a pair of mobile chromophores has been determined by solving the stochastic Liouville equation numerically. The configurations of the chromophore pair were chosen in such a way that for the static case the energy transfer rate is zero. A restrictive molecular reorientation diffusion model is introduced in order to describe the reorientation of the chromophores. This motion introduces a fluctuating dipole-dipole coupling between the chromophores, and thus opens the energy transfer channel. We observe no qualitative difference between the relaxation behaviour of the time-correlation function < χ_1(t)χ_1(0) > in the strong coupled or slow motion regime and the weak coupled or perturbation regime. (χ_1(t) refers to the probability that the initially excited chromophores remains excited at time t.) This finding may introduce a serious complication when intermolecular distances are extracted from fluorescence anisotropy measurements. The absence of cross-correlation effects between the energy transfer process and molecular reorientation in the fluorescence anisotropy correlation function is also analysed in detail.