RET between like molecules. Excitation energy migration in assemblies of chromophores

RET between like molecules. Excitation energy migration in assemblies of chromophores 

We have considered so far non-radiative energy transfer from a donor to an acceptor that is a different molecule (heterotransfer). Energy transfer between like molecules is also possible (homotransfer) if there is some overlap between the absorption and fluorescence spectra. 

In an assembly of chromophores, the process can repeat itself so that the excitation migrates over several molecules it is called excitation transport, or energy migration. 

Homotransfer does not cause additional de-excitation of the donor molecules, i.e. does not result in fluorescence quenching. In fact, the probability of de-excitation of a donor molecule does not depend on the fact that this molecule was initially excited by absorption of a photon or by transfer of excitation from another donor molecule. Therefore, the fluorescence decay of a population of donor molecules is not perturbed by possible excitation transport among donors. Because the transition dipole moments of the molecules are not parallel (except in very rare cases), the polarization of the emitted fluorescence is affected by homotransfer and information on the kinetics of excitation transport is provided by the decay of emission anisotropy. 

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