The impact of solid solution composition on kinetics and mechanism of [2 + 2] photodimerization of cinnamic acid derivatives

Abstract

The effect of the solid solution composition on the kinetics of solid-state [2 + 2] photocycloadditions was evaluated via a combination of single crystal XRD, FTIR, Raman spectroscopy, and principal component analysis (PCA).

Visualizing a Single‐Crystal‐to‐Single‐Crystal [2+2] Photodimerization through its Lattice Dynamics: An Experimental and Theoretical Investigation

“…Notably, one cannot help noticing that the value of the constant is very close to what found from the ATR-FTIR kinetic analysis by PCA on the single crystal of the same compound. [22] This validates the assumption that the chemical reaction, monitored by the evolution of the intramolecular IR spectrum, and the lattice transformation, followed via the evolution of the intermolecular Raman spectrum, do occur simultaneously. It also represents a striking difference compared to crystal-to-crystal heterogenous reactions, for which Raman measurements spanning both spectral ranges [13,16] have clearly demonstrated that the phase reconstruction takes place with a measurable time delay with respect to the chemical event.…”

“…In Figure S2 the corresponding lattice phonon Raman spectrum for the photodimerization reaction of the system [1H]Cl is also reported. Even though the transformation of [1H]Cl to its dimer takes place on longer time scales, [22] the spectral trend displayed is the same as for [1H]Br.…”

“…Reagent grade solvents and bi‐distilled water were used. The salt [ 1 H]Br (for its structure see Figure 1) was synthesized following the previously reported procedures: [22] 200 mg (1.23 mmol) of 4‐aminocinnamic acid ( 1 ) were suspended in 5 mL of water and neutralized with HBr acid. The material undissolved was filtered off and the remaining solution was left to evaporate slowly in the dark.…”

“…[21,23] In the work of Ref. [22] we investigated the effect of composition on the kinetics of the photoreaction in the series [1H]Br x Cl 1À x (0 < x < 1) making use of Raman and IR spectra in the intramolecular energy range and unraveled the chemical information conveyed by the latter spectroscopic technique by adopting a principal component analysis (PCA) approach. We thus observed that the time-evolution of the low-wavenumber Raman spectrum was markedly different from that recorded for crystal-to-crystal heterogeneous reactions.…”

“…In the work of Ref [22] . we investigated the effect of composition on the kinetics of the photoreaction in the series [ 1 H]Br x Cl 1−x (0<x<1) making use of Raman and IR spectra in the intramolecular energy range and unraveled the chemical information conveyed by the latter spectroscopic technique by adopting a principal component analysis (PCA) approach.…”