偶氮苯光致順反異構化反應機構爭議的介紹

A Story about Rotation-Inversion Controversy on Photoisomerization Mechanism of trans-Azobenzene

刁維光(Eric Wei-Guang Diau)

《化學》 62卷3期 (2004/09) Pp. 339-348

https://doi.org/10.6623/chem.2004026

摘要

偶氮苯分子的光致順反異構化機制在文獻報導中長期以來一直存在著極大的爭議而被理論化學家及光譜動力學者廣為探討。本文即著眼於此爭議的起源，利用高階理論計算的結果以及超快光譜實驗的數據，詳盡地分析了其可能的光化學反應路徑與激發態動力學間的關聯性以試圖解決此一爭議。我們的結論是，反式偶氮苯的順反異構化過程基本上應由其第一激發態的「轉動機制」來主導，但是當此轉動路徑因化學結構上的修飾或在限制性的環境中而堵塞時，其激發態至基態的緩解過程將由對稱的「雙反轉機制」來取代，而其順反異構化的過程則將會在基態上發生。我們否定了其順反異構化在激發態經由「反轉機制」而發生的可能性，但是我們並未排除此機制最後在基態上發生的可能性。

關鍵字

偶氮苯 ； 光致變色 ； 圓錐交叉 ； 全始計算 ； 螢光非等向性

並列摘要

The subject on photoisomerization mechanism of azobenzene has been debated for almost two decades. As a result, numerous investigations have been carried out in recent years to address the fundamental issue for the isomerization going through either an inversion or a rotation channel. This article reviews the source of the ＂inversion-rotation controversy＂ and systematically analyses the existing data based on both high-level theoretical calculations and ultrafast spectroscopic experiments. The conclusion was made for that the rotation channel rather than the conventional inversion channel is responsible for the observed excited-state relaxation dynamics of trans-azobenzene in a non-viscous solvent; when the rotation channel is obstructed by chemical modification, in a confined nano-space or in a viscous solvent, the concerted inversion channel operates to account for the observed ultrafast electronic deactivation through this channel. The following trans-to-cis photoisomerization in a rotation-blocked system should occur on the ground-state surface and the possibility of the involvement of the inversion mechanism in ground state is not excluded.

並列關鍵字

azobenzene ； photochromism ； conical intersection ； ab initio ； fluorescence anisotropy