where ℎ is Planck's constant, 𝑐𝑐 is the speed of light in a vacuum, 𝜇𝜇 e and 𝜇𝜇 g are dipole moments of excited-and ground-state, respectively, 𝑎𝑎 is an Onsager cavity radius of solute, 𝜀𝜀 is a permittivity of solvent, 𝐶𝐶 is a refractive index of solvent. This equation means that the Stokes shift from an absorption band to an emission band is proportional to the square of the difference in dipole moments between excited and ground states and varies on permittivity and refractive index of solvent. This equation allows us to estimate the excited-state dipole moments of the two conformers shown in Figure .