These microenvironments are very sensitive to solvent polarity, a term often used to describe how a solvent interacts with a solute molecule that encompasses several different electrostatic interactions. These interactions depend upon the dielectric constant, refractive index for the electronic response mentioned above, viscosity, and degree of hydrogen bonding of the solvent, resulting in a range of interactions upon a chromophore that has a significant change in dipole moment between ground and excited states. The contributions from each of these parameters is rather difficult to quantify, and as such the orientational polarizability of the solvent, which influences both the dielectric constant and refractive index of the solvent, is a clearer parameter to consider when investigating REEs. This orientational polarizability of a solvent simply describes how the dipole moment of the solvent is influenced by external electric fields, such as the changing dipole moment of a solute during photoexcitation.