Photochemical responses through multiple excitation and multiphoton absorption processes

Abstract

For molecules in condensed phase, three general restrictions limit the efficient utilization of light energies; first, molecules in higher excited states usually very rapidly relax to lower electronic states (Kasha's rule) and some portion of the absorbed photon energy is diminished in this relaxation, second, a large number of the molecules excited in assemblies undergo fast annihilation and only a small number of excited state molecules can remain, leading to the loss of the number of photons absorbed in the system. In addition, the electronic state accessible through the one- photon absorption is limited by the optical selection rule and we cannot access various dark electronic excited states of molecules. In the present article, we introduce several examples beyond these three restrictions in the photochemical responses of molecules and molecular assemblies through the multiple excitation and multiphoton processes.