Statistics for fluorescence photons of donor and acceptor molecules involved in non-radiative energy transfer (FRET)

Fluorescence of single molecular pairs involved in Förster Resonance Energy Transfer (FRET) is considered. Cases when either a donor of the electronic excitation energy or its acceptor has a non-fluorescent ''dark'' state are described. The influence of such dark states on energy transfer efficiency is analytically studied. Statistics for the number of donor/acceptor photons emitted per bin time is applied for these studies. Experimental distributions for photons of single emitters with ''dark'' states are presented, as well as their multivariate approximations with simulated distributions. It gives an example of how emitter parameters necessary for FRET efficiency calculations (transitions to and from the dark state) can be determined from the experimental statistics