We report on a time-resolved spectroscopic study aimed to shed light on the photoinduced valence tautomeric interconversion occurring in [Co(Me(4)cyclam)DBSQ](+). This compound belongs to the family of cobalt-dioxolene complexes, a class of compounds that was shown to undergo interconversion between the diamagnetic species Co-III-Cat and the paramagnetic one Co-II-Sq by the effect of several different perturbations: temperature, pressure, light absorption. Previous studies, with nanosecond and sub-nanosecond time resolution, have demonstrated the feasibility of light-induced interconversion in such systems and measured the charge recombination time. For the first time we have characterised the process with sub-picosecond time resolution, demonstrating the involvement of at least three different states in a two-step process. (C) 2002 Elsevier Science B.V. All rights reserved.