Practice question

After photon absorption, fluorophore attains upper vibrational level of S1. Within picoseconds it undergoes internal conversion, vibrational cooling and solvent reorganization, releasing portion of energy non-radiatively as heat to surrounding bath. Emission then originates from lowest vibrational level of S1, carrying less energy than initial excitation, hence longer wavelength. This energy loss process underlies Stokes shift, essential for separating excitation and emission in microscopy filters. Light scattering is wavelength elastic, absorption error would not systematically increase wavelength, triplet transfer gives phosphorescence.