The degree of polarization is expressed by fluorescence anisotropy, r(t), defined as r(t ) = (I//(t ) − I⊥(t ))/(I//(t ) + 2I⊥(t ))(2) where I∥(t) and I⊥(t) are the intensities of the fluorescence component at time t with the polarization parallel with and
perpendicular to the excitation light, respectively.