Non-radiative @E02256@ between two molecular entities separated by distances considerably exceeding the sum of their van der Waals radii. It describes the transfer in terms of the interaction between the @T06460@ of the entities in the very weak dipole-dipole @C01025@ limit. It is a Coulombic interaction frequently called a dipole-dipole @C01025@. The transfer @O04322@ from donor to acceptor, \(k_{\text{T}}\), is given by \[k_{\text{T}} = k_{\text{D}}\left ( \frac{R_{0}}{r} \right )^{6}=\frac{1}{\tau _{D}^{0}}\left ( \frac{R_{0}}{r}\right )^{6}\] where \(k_{\text{D}}\) and \(\tau_{\text{D}}^{0}\) are the @E02056@ @O04322@ and the @L03515@ of the excited donor in the absence of transfer, respectively, \(r\) is the distance between the donor and the acceptor and \(R_{0}\) is the @F02488@ or Förster radius, i.e., the distance at which transfer and spontaneous decay of the excited donor are equally probable (\(k_{\text{T}} = k_{\text{D}}\)) (see Note 3). \(R_{0}\) is given by \[R_{0} = Const.\left ( \frac{\kappa^{2}\mathit{\Phi}_{D}^{0}J }{n^{4}} \right )^{1/6}\] where \(\kappa\) is the orientation factor, \(\mathit{\Phi} _{D}^{0}\) is the @F02453@ @Q04991@ of the donor in the absence of transfer, \(n\) is the average @R05240@ of the medium in the @W06659@ range where @S05818@ is significant, \(J\) is the @S05818@ integral reflecting the degree of overlap of the donor @E02060@ with the acceptor @A00043@ and given by \[J = \int _{\lambda }I_{\lambda}^{D}(\lambda)\epsilon _{A}\left ( \lambda \right )\lambda^{4}\text{d}\lambda\] where \(I_{\lambda}^{D}(\lambda)\) is the normalized @S05827@ of the donor so that \(\int_{\lambda}I_{\lambda}^{D}(\lambda)\text{d}\lambda = 1\). \(\varepsilon_{\text{A}}({\lambda})\) is the @M03972@ of the acceptor. See Note 3 for the value of \(Const.\).