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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Theoretical study of the isomerization mechanism of azobenzene and disubstituted azobenzene derivatives
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Theoretical study of the isomerization mechanism of azobenzene and disubstituted azobenzene derivatives

机译：偶氮苯与二取代偶氮苯衍生物异构化机理的理论研究

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A series of azobenzenes was studied using ab initio methods to determine the substituent effects on the isomerization pathways. Energy barriers were determined from three-dimensional potential energy surfaces of the ground and electronically excited states. In the ground state (S-0), the inversion pathway was found to be preferred. Our results show that electron donating substituents increase the isomerization barrier along the inversion pathway, whereas electron withdrawing substituents decrease it. The inversion pathway of the first excited state (S-1) showed trans -> cis barriers with no curve crossing between S-0 and S-1. In contrast, a conical intersection was found between the ground and first excited states along the rotation pathway for each of the azobenzenes studied. No barriers were found in this pathway, and we therefore postulate that after n -> pi* (S-1 <- S-0) excitation, the rotation mechanism dominates. Upon pi -> pi* (S-2 <- S-0) excitation, there may be sufficient energy to open an additional pathway (concerted-inversion) as proposed by Diau. Our potential energy surface explains the experimentally observed difference in trans-to-cis quantum yields between S-1 and S-2 excitations. The concerted inversion channel is not available to the remaining azobenzenes, and so they must employ the rotation pathway for both n -> pi* and pi -> pi* excitations.
机译：使用从头算方法研究了一系列偶氮苯，以确定取代基对异构化途径的影响。根据基态和电子激发态的三维势能面确定能垒。在基态（S-0）下，发现反转途径是优选的。我们的结果表明，给电子取代基沿反演途径增加了异构化势垒，而吸电子取代基则降低了异构化势垒。第一激发态（S-1）的转化途径显示出反式->顺式势垒，在S-0和S-1之间没有曲线交叉。相反，对于所研究的每种偶氮苯，沿旋转路径在基态和第一激发态之间发现了一个圆锥形相交。在该途径中未发现障碍，因此我们假设在n-> pi *（S-1 <-S-0）激发之后，旋转机制起主导作用。当pi-> pi *（S-2 <-S-0）激发时，可能有足够的能量打开Diau提出的另一条途径（经证明的反演）。我们的势能面解释了实验观察到的S-1和S-2激发之间反式-顺式量子产率的差异。剩余的偶氮苯无法使用协调的反型通道，因此它们必须对n-> pi *和pi-> pi *激发都采用旋转途径。

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