Probing Organometallic Reactions by Time-Resolved Infrared Spectroscopy in Solution and in the Solid State Using Quantum Cascade Lasers

The photochemistry and photophysics of metal carbonyl compounds (W(CO)₆,Cp*Rh(CO)₂ (Cp* = η⁵-C₅Me₅), and fac-[Re(CO)₃(4,4'-bpy)₂Br] [bpy = bipyridine]) have been examined on the nanosecond timescale using a time-resolved infrared spectrometer with an external cavity quantum cascade laser (QCL) as the infrared source. We show the photochemistry of W(CO)₆ in alkane solution is easily monitored, and very sensitive measurements are possible with this approach, meaning it can monitor small transients with absorbance changes less than 10-⁶ DOD. The C–H activation of Cp*Rh(CO)(C₆H₁₂)to form Cp*Rh(CO)(C₆H₁₁)H occurs within the first few tens of nanoseconds following photolysis, and we demonstrate that kinetics obtained following deconvolution are in excellent agreement with those measured using an ultrafast laser-based spectrometer. We also show that the high flux and tunability of QCLs makes them suited for solid-state and time-resolved measurements.