Changes in electronic structure are the source of structural modifications in photochem. and photobiol. processes, occurring at ultrafast time scales (between femto- and picosecond times). An original method to probe these changes based upon a pump probe method combining ultrafast lasers and pulsed x-rays from a synchrotron light source was developed. Detection of electronic changes is based upon x-ray absorption spectroscopy. One of the interesting aspects of this spectroscopy lies in the possibility of studying disordered media such as liqs., an essential point in chem. and biol. Results on coordination chem. complexes showing the advantages of this approach are presented.