Applications of time-resolved step-scan Fourier-transform infrared spectroscopy in revealing the light-initiated reactions in condensed phases

Step-scan Fourier-transform infrared spectroscopy (ssFTIR) simultaneously provides the spectroscopic and kinetic information of a given reaction. ssFTIR has been extensively employed to acquire the transient absorption and emission spectra in gas phase for identifying unstable species, for example, various Criegee intermediates, and elucidating the dynamics and kinetics of the reaction, such as the molecular elimination dynamics of haloalkenes and the bimolecular reactions involving chlorine atoms and singlet oxygen atoms. In addition to gaseous studies, ssFTIR has been also utilized to record the time-resolved difference spectra of the photochemical reactions in condensed phases, such as the photolysis of metal–ligand complexes, photocycles of the retinal proteins, coordination capability of solvents to unstable transient species, chemical reactions of atmosphere-related molecules in aqua, and the exciplex dynamics of organic light emitting materials. Moreover, my group has pioneered the recording of the transient thermal infrared emission of gold nanostructures upon photoexcitation. The experimental setups and the working principles for probing the time-resolved infrared absorption and emission in condensed phases will be revealed and a number of studies on chemical, biological, and materials systems will be described. These reported results demonstrate that ssFTIR is a versatile tool for exploring the properties of novel materials and photoreactions in condensed phases.