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首页> 外文期刊>Chemistry: A European journal >Photochemical and Electronic Properties of Conjugated Bis(azo)Compounds:An Experimental and Computational Study
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Photochemical and Electronic Properties of Conjugated Bis(azo)Compounds:An Experimental and Computational Study

机译：共轭双（偶氮）化合物的光化学和电子性质：实验和计算研究

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We have investigated the photophysical,photochemical and electrochemical properties of two bis(azo)derivatives,(E,E)-m-1 and(E,E)-p-1.The two compounds,which can be viewed as being composed of a pair of azobenzene units sharing one of their phenyl rings,differ only for the relative position of the two azo groups on the central phenyl ring-meta and para for m-1 and p-1,respectively.The UV-visi-ble absorption spectra and photoiso-merisation properties are noticeably different for the two structural isomers;(E,E)-m-1 behaves similarly to(E)-azobenzene,while(E,E)-p-1 exhibits a substantial red shift in the absorption bands and a decreased photoreactivity.The three geometric isomers of m-1,namely the E,E,E,Z and Z,Z isomers,cannot be resolved in a mixture by absorption spectroscopy,while the presence of three distinct species can be revealed by analysis of the absorption changes observed upon photoisomeri-sation of(E,E)-p-1.Quantum chemical ZINDO/1 calculations of vertical excitation energies nicely reproduce the observed absorption changes and support the idea that,while the absorption spectra of the geometrical isomers of m-1 are approximately given by the sum of the spectra of the constituting azobenzene units in their relevant iso-meric form,this is not the case for p-1.From a detailed study on the E->Z photoisomerisation reaction it was observed that the photoreactivity of an azo unit in m-1 is influenced by the iso-meric state of the other one.Such observations indicate a different degree of electronic coupling and communication between the two azo units in m-1 and p-1,as confirmed by electrochemical experiments and quantum chemical calculations.The decreased photoisomerisation efficiency of(E,E)-p-1 compared to(E,E}-m-1 is rationalised by modelling the geometry relaxation of the lowest pi-pi~* state.These results are expected to be important for the design of novel oligomers and polymers,based on the azobenzene unit,with predetermined photoreactivity.
机译：我们研究了两种双（偶氮）衍生物（E，E）-m-1和（E，E）-p-1的光物理，光化学和电化学性质。这两种化合物可以看做是由一对共享一个苯环的偶氮苯单元，分别仅对中心苯环的间偶氮和对位的两个偶氮基的相对位置分别为m-1和p-1.UV可见吸收两种结构异构体的光谱和光致异构化性质明显不同;（E，E）-m-1的行为与（E）-偶氮苯相似，而（E，E）-p-1在m-1的三个几何异构体，即E，E，E，Z和Z，Z异构体，不能通过吸收光谱法在混合物中分离，而可以存在三种不同的物质通过对（E，E）-p-1光异构化时观察到的吸收变化的分析揭示了这一点。垂直激发能的量子化学ZINDO / 1计算很好地再现了观察到的吸收变化，并支持了这样的观点，即m-1的几何异构体的吸收光谱近似由构成其相关异构形式的偶氮苯单元的光谱之和给出，但不是通过对E-> Z光异构化反应的详细研究，我们发现m-1中偶氮单元的光反应性受另一个异构体的异构状态影响。通过电化学实验和量子化学计算证实，m-1和p-1中两个偶氮单元之间电子偶联和通讯的程度不同。（E，E）-p-1与（E，通过对最低pi-pi〜*状态的几何弛豫进行建模，可以使E} -m-1合理化。这些结果对于基于偶氮苯单元并具有预定光反应性的新型低聚物和聚合物的设计具有重要意义。

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