Hybrid hard- and soft-modelling applied to analyze ultrafast processes by femtosecond transient absorption spectroscopy: Study of the photochromism of salicylidene anilines

Deconvolution of femtosecond time‐resolved spectroscopy data in multivariate curve resolution. Application to the characterization of ultrafast photo‐induced intramolecular proton transfer

“…The kinetic scheme was designed to roughly model the photodynamic properties of SA in solution (see Figure 1). The characteristic time, 50 fs, associated with k 2 would correspond to the ESIPT [7,30,31,33]. The rate constant k 1 typically would describe an ultrafast transition ($ few femtoseconds) between the ground state and the excited state, which is usually not accessible from classical experimental data.…”

“…The rate constant k 1 typically would describe an ultrafast transition ($ few femtoseconds) between the ground state and the excited state, which is usually not accessible from classical experimental data. The rate constants k 3 would correspond to the formation of a cis-keto intermediate ($200 fs) [7,32]. Finally, k 4 would correspond to the relaxation of this intermediate to the trans-keto photochromic form ($2 ps).…”

“…Additionally, nonlinear optical effects may also distort the measured signals [5,6]. This latter issue can be dealt with by analyzing multi-experiment data with multivariate curve resolution (MCR), as recently reported [7]. In the current work, we first bring our attention to the characterization of the time resolution assessing the instrumental response function (IRF) from the measurement of pump-probe crosscorrelation signal [6,8].…”

“…Furthermore, MCR methods can be extended to include refinement of the time-dependent concentration profiles (more generally any profiles) fitting them with a kinetic model (hard-model) to assess reaction constants and increase the robustness of the resolution [16,17]. The potential of this kind of approach mixing hard-and soft-modeling has been shown in time-resolved spectroscopy [7,9,10,18]. As time resolution is usually a few hundreds of femtoseconds, any transient phenomena occurring faster, or on the same timescale, are affected by the convolution of the true kinetics with the IRF.…”

“…The detailed mechanism is still controversial but the ESIPT usually occurs in less than 50 fs in solution [29][30][31][32][33][34]. In the previous analysis [7], new insights into the photo-reaction were obtained but as deconvolution was not considered, the kinetic analysis had to be considered very carefully at ultrashort time scale.…”