Ten-nanosecond step-scan FT-IR absorption difference time-resolved spectroscopy: Applications to excited states of transition metal complexes

Ten-nanosecond time resolution has been achieved with step-scan FT-IR absorbance difference spectroscopy ((SFT)-F-2-IR Delta A TRS) and demonstrated by measuring Delta A spectra of fac-[Re(bpy)(CO)(3)Cl] and cis-[Os(bpy)(2)(CO)(4,4'-bpy)](2+) (bpy = 2,2'-bipyridine; 4,4'-bpy=4,4'-bipyridine) in CH3CN solution, following 355-nm laser excitation, In both complexes, the large shifts in <(nu)over bar>(CO) to higher energy are consistent with the assignment that the loffest-energy excited states are metal-to-ligand charge transfer in nature. For [Os(bpy)(2)(Co)(4,-4'-bpy)](2+), it is also possible to measure the excited-state decay kinetics, again with 10-ns resolution. In addition, Delta A bands are observed that are related to excited-state vibrations of the bipyridine ligands. Delta A spectra of good signal-to-noise ratio ran be obtained for complexes with lifetimes as short as 10 ns.