A new form of analytical chemistry: distinguishing the molecular structure of photo-induced states from ground-states.

This paper introduces a new analytical technique from the field of crystallography, and the optoelectronics motivation that underpins this effort. The essence of the photocrystallography technique is explained in the context of a four-dimensional (space-time) structural probe, and the four technically distinct time-windows of enquiry are presented. This features the complementary needs of laboratory, synchrotron and Free-electron laser based X-ray diffraction experiments. The different scales of atomic resolution required for the technique to be able to probe various photochemical phenomena are described. Sample requirements for photocrystallography experiments are also considered. The paper concludes by forecasting the prospective fortune of this new analytical technique to respond to major current challenges in the photovoltaic, optical data storage, and non-linear optics industries.