The excited electron: photophysical properties

After a review of fundamental notions such as absorption, emission and the properties of excited states, the chapter introduces excited-state electron transfer. Several examples are given, using molecules to realize photodiodes, light emitting diodes, photovoltaic cells, and even harnessing photochemical energy for water photolysis. The specificities of ultrafast electron transfer are outlined. Energy transfer is then defined, starting from its theoretical description, and showing its involvement in photonic wires or molecular assemblies realizing an antenna effect for light harvesting. Photomagnetic effects; that is, the modification of magnetic properties after a photonic excitation, are then studied. The examples are taken from systems presenting a spin cross-over, with the LIESST effect, and from systems presenting metal–metal charge transfer, in particular in Prussian Blue analogues and their molecular version.