We describe an experimental setup, which measures transient chemical changes of photoexcited solutes in disordered systems via time-resolved X-ray Absorption Spectroscopy (XAS) with picosecond temporal resolution. The setup combines a femtosecond amplified laser with picosecond X-ray pulses at beamline 5.3.1 at the Advanced Light Source in Berkeley, USA. New results on time-resolved XAS used for probing both the electronic and the geometric modi. cations of a photoexcited tris-(2,2'-bipyridine) ruthenium (II), Ru-II(bpy)(3) in water solution are presented.