In situ and real-time ultrafast spectroscopy of photoinduced reactions in perovskite nanomaterials.

By employing two synchronized mode-locked femtosecond lasers and interferometric detection of the pump-probe spectra-referred to as asynchronous and interferometric transient absorption-we have developed a method for broad dynamic range and rapid data acquisition. Using asynchronous and interferometric transient absorption, we examined photochemical changes during femtosecond pump-probe experiments on all-inorganic cesium lead halide nanomaterials. The laser pulse train facilitates photoreactions while allowing real-time observation of charge carrier dynamics. In perovskite nanocrystals undergoing photo-substitution of halide anions, transient absorption spectra showed increasing bandgap energy and faster relaxation dynamics as the Cl/Br ratio increased. For colloidal perovskite nanoplatelets, continuous observation revealed both spectral and kinetic changes during the light-induced coalescence of nanoplatelets, by analyzing temporal segments. This integrated technique not only deepens understanding of exciton dynamics and environmental influences in perovskite nanomaterials but also establishes asynchronous and interferometric transient absorption as a transformative tool for real-time observation of photochemical dynamics.