Time-resolved relaxation studies of spin crossover systems in solution

This chapter focuses on the kinetics of spin-state relaxation, primarily in iron(II) complexes in solution. Initial work carried out during the 1970s and early 1980s by chemical relaxation methods is briefly reviewed, followed by a more detailed account of the laser photoperturbation technique and the photophysics which underpin this approach, now widely adopted as the method of choice for spin crossover relaxation studies in solution. The use of time-resolved vibrational spectroscopy as an alternative to conventional spectrophotometric probing of the spin crossover relaxation process is described. The results of variable temperature and pressure studies on a variety of spin crossover complexes are also considered, particularly with reference to strategies for the control of spin state lifetimes through design of ligand structures.