The photochromic processes present considerable interest for the development of optical memory devices, optical sensors and solar cells. On the basis of reversible S-radicals (RS•) binding to the plane metal complexes we have developed interesting and promising new photochromic systems. The convenient sources of S-radicals are the organic disulfides and plane Ni(II) complexes with sulfur- and nitrogen-containing ligands (NiL2) were selected as the trap of S-radicals. By laser flash photolysis method we have shown that practically all S-radicals appearing at the photodissociation of a series of disulfides with high rate constants reversibly coordinate to the plane Ni(II) complexes with the formation of (RS•)NiL2 radical complexes. Its individual lifetime is determined by the escape of S-radical out of coordination sphere and depends on the nature of complex and radical. However, the repeated coordination of S-radical increases lifetime by two-three orders in some cases up to seconds. The systems come back to initial state due to recombination of S-radicals. Intensive absorption bands of (RS•)NiL2 in UV and visible region provide fine photochromic properties and good fatigue resistance (> 104 number of transformations without degradation). Application of stable NO radicals which react with S-radicals allows to measure the absorption coefficients and rate constants of recombination of S-radicals and their coordination to NiL2. Careful analysis of transient absorption spectra and kinetics has shown the formation of (RS•)2 NiL2 biradical complexes for some systems. Both type of radical complexes decay in the dissociation reaction with the release of free S-radical. Fast measurements in wide temperature range give information on activation energies of photoinduced processes and allow to estimate the energy of RS•–Ni bond.