Table 1.

Basal equations for FRET.

(1)	Definition of energy transfer rate kT
	R0 depends on the refractive index of the medium n, the orientation factor κ2, the fluorescence quantum yield ΦD, the normalized fluorescence spectrum of the donor FD (λ) and the molar absorptivity of the acceptor εA (λ), and the wavelength λ in cm: $$R_0=\frac{9000\text{\hspace{0.17em}ln}10{\kappa }^2{\Phi }_D}{128{\pi }^5{n}^4{N}_A}{\displaystyle {\int }_0^{\infty }\frac{F_D\left(\lambda \right){\epsilon }_A\left(\lambda \right)d\lambda }{{\lambda }^4}}$$
(2)	Distance-dependency of energy transfer efficiency E
	The efficiency E of energy transfer is the product of kT times the unperturbed donor lifetime τD and varies as the inverse sixth power of the ratio of the distance R between donor and acceptor and the Förster radius R0: $$E=\frac{k_T{\tau }_D}{1+k_T{\tau }_D}=\frac{1}{1+{\left(R/R_0\right)}^6}$$
(3)	Definition of energy transfer rate kT
	kT depends on the Förster radius R0, the distance R separating the chromophores and the unperturbed donor fluorescence lifetime τD: $$k_T=\frac{1}{{\tau }_D}{\left(\frac{R_0}{R}\right)}^6$$