Trans–cis photoisomerization is generally described by a model in which the reaction proceeds via a common intermediate having a perpendicular conformation around the rotating bond, irrespective of from which isomer the reaction starts. Nevertheless, such an intermediate has yet to be identified unambiguously, and it is often called the ‘phantom’ state. Here we present the structural identification of the common, perpendicular intermediate of stilbene photoisomerization using ultrafast Raman spectroscopy. Our results reveal ultrafast birth and decay of an identical, short-lived transient that exhibits a vibrational signature characteristic of the perpendicular state upon photoexcitation of the trans and cis forms. In combination with ab initio molecular dynamics simulations, it is shown that the photoexcited trans and cis forms are funnelled off to the ground state through the same, perpendicular intermediate.

反式-顺式光异构化通常通过一个模型来描述，其中反应通过在旋转键周围具有垂直构象的共同中间体进行，无论反应从哪个异构体开始。然而，这样的中间体尚未被明确识别，它通常被称为“幻影”状态。在这里，我们使用超快拉曼光谱对二苯乙烯光异构化的常见垂直中间体进行结构鉴定。我们的结果揭示了相同的、短暂的瞬态的超快诞生和衰变，该瞬态在反式和顺式形式的光激发下表现出垂直态的振动特征特征。结合从头算分子动力学模拟，结果表明光激发的反式和顺式形式通过相同的垂直中间体汇集到基态。