Université Lille-Nord de France, LASIR, CNRS-UMR 8516, F-59655 Villeneuve d'Ascq, France.
Anal Chim Acta. 2013 Jul 25;788:8-16. doi: 10.1016/j.aca.2013.06.027. Epub 2013 Jun 24.
The main advantage of multivariate curve resolution - alternating least squares method (MCR-ALS) is the possibility to act as multiset analysis method, combining data coming from different experiments to provide a complete and more accurate description of a chemical system. Exploiting the multiset side, the combination of experiments obtained from two photo-active systems with complementary pathways and monitored by femtosecond UV-vis transient absorption spectroscopy is presented in this work. A multiset hard- and soft-multivariate curve resolution model (HS-MCR) was built allowing the description of the spectrokinetic features of the entire system. Additionally, reaction quantum yields were incorporated in the hard-model in order to describe branching ratios for intermediate species. The photodynamics of salicylidene aniline (SA) was investigated as a case study. The overall reaction scheme involves two competitive and parallel pathways. On the one hand, a photoinduced excited state intramolecular proton transfer (ESIPT) followed by a cis-trans isomerization leads to the so-called photochromic form of the molecule, which absorbs in the visible. The formation of the photochromic species is well characterized in the literature. On the other hand, a complex internal rotation of the molecule takes place, which is a competing reaction. The rotation mechanism is based on a trans-cis isomerization. This work aimed at providing a detailed spectrokinetic characterization of both reaction pathways for SA. For this purpose, the photodynamics of two molecules of identical parent structures and different substituent patterns were investigated in femtosecond transient absorption spectroscopy. For SA, the mechanism described above involving the two parallel pathways was observed, whereas for the derivative form of SA, the photochromic reaction was blocked because of the replacement of an H atom by a methyl group. The application of MCR approaches enabled to obtain transient spectra for the different intermediate species involved and rate constants for the photochromic reaction, thus contributing to a comprehensive description of the photodynamics of SA.
多元曲线分辨-交替最小二乘法（MCR-ALS）的主要优势在于它可以作为多集分析方法，将来自不同实验的数据结合起来，提供对化学系统更完整、更准确的描述。本文利用多集的优势，结合了两种光活性体系的实验结果，这两个体系具有互补的途径，并用飞秒紫外-可见瞬态吸收光谱进行监测。建立了多集硬软多元曲线分辨模型（HS-MCR），可以描述整个体系的光谱动力学特征。此外，还在硬模型中加入了反应量子产率，以描述中间物种的分支比。以水杨醛苯胺（SA）为例研究了光动力学。总的反应方案涉及两个竞争性和并行的途径。一方面，光诱导的激发态分子内质子转移（ESIPT）随后发生顺式-反式异构化，导致分子的所谓光致变色形式，其在可见光中吸收。光致变色物种的形成在文献中有很好的描述。另一方面，分子发生复杂的内部旋转，这是一个竞争反应。旋转机制基于 trans-cis 异构化。这项工作旨在为 SA 的两种反应途径提供详细的光谱动力学特征。为此，在飞秒瞬态吸收光谱中研究了两个具有相同母体结构和不同取代模式的分子的光动力学。对于 SA，观察到了上述涉及两个平行途径的机制，而对于 SA 的衍生物，由于 H 原子被甲基取代，光致变色反应被阻断。MCR 方法的应用能够获得不同中间物种的瞬态光谱和光致变色反应的速率常数，从而有助于对 SA 的光动力学进行全面描述。
