Transient absorption spectroscopy. Femtosecond transient absorption spectroscopy was done using a setup consisting of a mode-locked Ti:sapphire laser and regenerative amplifier (Astrella, Coherent Inc.) operating at a repetition rate of 1 kHz to generate a 100 fs pulsed beam centered at 800 nm. The output beam was split into pump and probe beams. The pump beam was sent to an optical parametric amplifier (OPerA Solo, Coherent Inc.) to obtain the desired wavelength of the pump beam. The probe beam was focused into a 4 mm CaF2 crystal to generate a 350-750 nm white light continuum that was continuously translated with a linear stage (Newport MFACC) to avoid damage to the crystal. The probe beam was focused into the sample, while the pump was focused behind the sample, effectively resulting in a 2:3 beam size ratio that ensures most efficient probing of the transient molecules. The angle between pump and probe polarizations was set to 54.7° to minimize the influence of molecular rotations on the ultrafast kinetics. After transmitting through the sample, the probe beam was directed into an optical fiber and input into a CCD spectrograph (Ocean Optics, Flame-S-UV-vis-ES). Data acquisition was performed using custom LabVIEW (National Instruments) software. Data processing (background subtraction, outlier removal, and averaging) was done in a custom LabView data processing program, while chirp correction was performed via CarpetView (Light Conversion). Global fitting analysis was performed using the global analysis function in CarpetView. Reported time constants with standard deviations were calculated as averages from three separate data sets. Numerous sequential models were tested, and their quality was evaluated based on the agreement between the calculated component spectra and the temporal evolution of the timeresolved spectra.