Ten-Nanosecond Step-Scan FT-IR Absorption Difference Time-Resolved Spectroscopy: Applications to Excited States of Transition Metal Complexes

Abstract

Ten-nanosecond time resolution has been achieved with step-scan FT-IR absorbance difference spectroscopy (S²FT-IR ΔA TRS) and demonstrated by measuring ΔA spectra of fac-[Re(bpy)(CO)₃Cl] 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 (CO) to higher energy are consistent with the assignment that the lowest-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, ΔA bands are observed that are related to excited-state vibrations of the bipyridine ligands. ΔA spectra of good signal-to-noise ratio can be obtained for complexes with lifetimes as short as 10 ns.

Keywords

Time-resolved IR Step-scan FT-IR Bipyridine complexes Metal-to-ligand charge transfer Transition metal complex photophysics

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