Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, D-24098 Kiel, Germany.
Photochem Photobiol Sci. 2013 Mar;12(3):511-8. doi: 10.1039/c2pp25291k. Epub 2012 Dec 7.
A systematic study is reported of the photochemical properties of the multi-azobenzene compounds bis[4-(phenylazo)phenyl]amine (BPAPA) and tris[4-(phenylazo)phenyl]amine (TPAPA) compared to the parent molecule 4-aminoazobenzene (AAB). The bis- and tris-azobenzenes were synthesised by a variant of the Ullmann reaction and exist in their stable all-E forms at room temperature. Striking changes in the spectral positions and intensities of their first ππ* absorption bands compared to AAB reveal strong electronic coupling between the AB units. The nature of the excited states was explored by quantum chemical calculations at the approximate coupled-cluster (CC2) level. Upon UV/VIS irradiation, the molecules isomerise to the Z-isomer (AAB), ZE- and ZZ-isomers (BPAPA), and ZEE-, ZZE- and ZZZ-isomers (TPAPA), respectively. The photoswitching behaviours were investigated by UV/VIS and NMR spectroscopies. All individual isomers were detected by one-dimensional (1D) (1)H NMR spectroscopy (BPAPA) and two-dimensional (2D) HSQC NMR spectroscopy (TPAPA). A kinetic analysis provided the isomer-specific thermal lifetimes. The variance of the thermal lifetimes demonstrates a dependence of the Z-E isomerisation on the chromophore size and number of AB units.
本文系统研究了多偶氮苯化合物双[4-(偶氮苯)苯基]胺（BPAPA）和三[4-(偶氮苯)苯基]胺（TPAPA）与母体分子 4-氨基偶氮苯（AAB）的光化学性质。双偶氮苯和三偶氮苯通过乌尔曼反应的变体合成，在室温下以其稳定的全 E 构象存在。与 AAB 相比，它们的第一个ππ*吸收带的光谱位置和强度发生了显著变化，这表明 AB 单元之间存在强烈的电子耦合。通过近似耦合簇（CC2）水平的量子化学计算探索了激发态的性质。在 UV/VIS 辐照下，分子分别异构化为 Z-异构体（AAB）、ZE 和 ZZ-异构体（BPAPA）以及 ZEE、ZZE 和 ZZZ-异构体（TPAPA）。通过 UV/VIS 和 NMR 光谱研究了光致开关行为。通过一维（1D）（1）H NMR 光谱（BPAPA）和二维（2D）HSQC NMR 光谱（TPAPA）检测到所有单个异构体。动力学分析提供了异构特异性热寿命。热寿命的变化表明 Z-E 异构化取决于发色团的大小和 AB 单元的数量。
