Figure 7.

Dependence of the DOF on the distance between fluorophores if the fluorophores are rotating without constraints. The DOF for the fast-rotating fluorophores (dashed line) is equal to $\frac{2}{3}$. The effective ensemble average DOF for the slow-rotating fluorophores (solid line, calculated from the FRET efficiency curve (Fig. 8)) is smaller because of depletion of the states with higher DOF values. The distance between the fluorophores in Figs. 7–10 is measured in units of $R_0\left(\frac{2}{3}\right)$ (the Förster radius for the fluorophores with ${\kappa }^2=\frac{2}{3}$).