A cobalt(III)-polydioxolene polymer undergoing valence tautomeric interconversion was irradiated at cryogenic temperatures. Magnetic and EPR data suggest the occurrence of photoinduced VT interconversion, with a maximum degree of about 10%. The kinetics data evidence a larger amount of cooperativity than previously observed in simple monomer, a phenomenon that we attribute to the ID nature of the system. In the range 9-40 K the relaxation time follows two different regimes, both temperature dependent. The small values of the activation energies suggest the existence of phonon assisted relaxation mechanisms based on a tunneling process involving the total-symmetric breathing mode of the complex. (c) 2006 Elsevier B.V. All rights reserved.