Fluorescence Why do stoke shifts occur Why are larger stoke

Fluorescence: Why do stoke shifts occur? Why are larger stoke shifts better?

Solution

The energy associated with fluorescence emission transitions is generally less than that of absorption, so the resulting emitted photons have less energy and are shifted to longer wavelengths. This phenomenon is known as Stokes Shift. This Stokes shift occurs for virtually all fluorophores commonly applicable in solutions which is under investigation. . The stokes shift is due to vibrational relaxatiopn and solvent reorganisation.

The larger stokes shift is better because, magnitude of Stokes shift is dependent on the fluorophore ( a dipole, surrounded by water molecules) and its environment. It is frequently due to non-radiative decay to the lowest vibrational energy level of the excited state and the emission of fluorescence frequently leaves a fluorophore in a higher vibrational level of the ground state.