X-ray Diffraction Investigation of the Nature and the Mechanism of Photoinduced Phase Transition in Molecular Materials

Laser driven solid–solid phase transition is a new kind of manipulation of matter by light which offers fascinating possibilities for controlling the switching of the physical properties of materials at the macroscopic state. This is possible by taking advantage of the cooperative interactions between the constituent molecules of the material. Slow dynamics phenomena are illustrated by the photo-induced spin transition, where long lived states can be generated at low temperature using cw excitation. A fast process is exemplified here by the neutral–ionic phase transition induced in a transient state on the 100-picosecond time-scale by a 100 femtosecond laser pulse. Self-amplification and self-ordering processes are discussed.