100 ps time-resolved crystallographic investigation of the photoinduced phase transition in TFF-CA

We report the structural investigation of photoinduced phase transitions between ionic and neutral macroscopic states in an organic charge-transfer molecular material, with 100 picosecond resolution, using pulsed X-rays from a synchrotron. A femtosecond laser pulse switches the material within the nanosecond from neutral to ionic and also from ionic to neutral macroscopic state by virtue of a strong cooperativity. Data collections show that a long range ferroelectric order takes place in the ionic photoinduced phase. A two step mechanism is observed in the transformation from ionic to neutral. This associated with a disordering process of ionic strings followed by a 3D reorganisation at a macroscopic scale. Key words. Photo-induced phase transition, Time-resolved x-ray diffraction