Although ESIPT reaction is generally very efficient and fast, two different types of emission band are often observed in ESIPT molecules depending on the nature of surrounding medium such as the solvent molecule. One emission band, predominantly observed in hydrocarbon and non-polar solvents, is large Stokes' shifted and usually structureless one, which is assigned to the emission from K*. Another band typically observed either in protic or polar solvents with rather normal Stokes' shift, is attributed to the emission from E* before undergoing ESIPT.32 The relative intensities of these two bands were found to vary according to the solvent conditions and molecular structures.33