Here we describe the rotational dynamics of a bond using the total effective correlation time, τ eff = N 0 αiτi, which is the weighted average of all timescales in a multiexponential decay assumed for g(t), and equals the area between correlation function and x-axis. Notably, τ eff is the total effective correlation time containing all rotational timescales, including internal and overall rotations. This definition is used previously, for example, by Levy et al. but slightly differs from effective correlation times of molecular internal motions used in Lipari-Szabo approach and for lipids in bilayers where effective correlation times include only internal motions with respect to molecule axes. Interestingly, by substituting Eq. 4 into Eq. 2 and using relation J(0) = 2τ eff , Redfield equation for R • 2 can be written as