Knowledge Bank

Relaxation processes Involving geometric conformotional changes of the lowest singlet state cause fluorescence to occur from the equilibrium excited state, Franck-Condon state, or an intermediate conformation depending on the relative magnitudes of the relaxation and fluorescence rate constents. Examples given include intramolecular twisting, solvent-cage relaxation, proton transfer and excimer formation. The dependence of fluorescence energy, yield, and lifetime on the viscosity, temperature, and medium will be discussed. Generalizations regarding such relaxation processes in electronically excited molecules will be derived.