Department Chemistry - Biology, University of Siegen, Adolf-Reichwein-Strasse 2, 57076, Siegen, Germany.
Chemphyschem. 2023 Jan 3;24(1):e202200512. doi: 10.1002/cphc.202200512. Epub 2022 Oct 18.
The fascinating field of thermo-halochromism of azo chromophores still astounds with unexplored facets nourished by the intricate relationship between molecular structure variations and their spectroscopic signatures. In this respect, we investigated the thermally dependent absorption behaviour of acrylamide derivatives of o-methyl red, characterised by two secondary amide linkages with hydrogen bonding-active protons in the pendant alkyl substituent. The systems were studied by a combination of UV-vis, derivative, and difference, as well as 2D-NMR (Nuclear Overhauser Effect Spectroscopy, NOESY) spectroscopy. These experiments show that the thermo-halochromism is specifically influenced by hydrogen bonding interaction of the secondary amidoalkyl acrylamide side chain with the azobenzene core in dependence of the spacer length. Apparently, the substituent acts like a solvent, which is directly tethered to the chromophore and where the tether length determines the interaction by conformational freedom. We refer to this novel phenomenon as "H-bonding-controlled thermo-halochromism".
偶氮生色团的热致变色现象令人着迷，其中分子结构变化与其光谱特征之间的复杂关系为人们提供了许多尚未探索的领域。在这方面，我们研究了邻甲酚红丙烯酰胺衍生物的热依赖性吸收行为，该衍生物具有两个次级酰胺键，在侧链烷基取代基中具有氢键活性质子。该体系通过紫外-可见分光光度法、导数和差光谱法以及二维 NMR（核 Overhauser 效应光谱学，NOESY）光谱法进行了研究。这些实验表明，热致变色现象主要受到次级酰胺基丙烯酰胺侧链与偶氮苯核心之间氢键相互作用的影响，这取决于间隔基的长度。显然，取代基的作用类似于直接连接在生色团上的溶剂，其中连接基团的长度通过构象自由度决定了相互作用。我们将这种新现象称为“氢键控制的热致变色现象”。
