Molecular photophysics

The history of photochemistry and molecular photophysics is closely linked to the use of phototherapy in medicine since antiquity, the observation of luminescence in the ^17th century and the invention of photography in the early ^19th century. Time-resolved spectroscopic techniques were to have a considerable impact on our understanding of photophysical and photochemical processes, and hence on our understanding of the nature of the electronic structure of molecules and the dynamics of molecular states in the second half of the ^twentieth century. Ronald Norrish and George Porter (winner of the 1967 Nobel Prize in Chemistry) developed photographic flash devices with millisecond to microsecond time resolution, enabling the observation of long-lived states such as triplet states. The invention of pulsed lasers increased temporal resolution, first to nanoseconds, then picoseconds and finally femtoseconds, making it possible to observe all the internal dynamics of molecules and understand reaction mechanisms. In particular, Ahmed Zewail developed "femtochemistry", enabling the detection of transition states and the analysis of coherence effects and laser pulse phase control, for which he was awarded the Nobel Prize in Chemistry in 1999.