Many photoactive proteins contain chromophores based on para-substituted phenolate anions which are an essential component of their electronic structure. Here, we present a reductionist approach to gain fundamental insight into the evolution of electronic structure as the chromophore increases in complexity from phenolate to that in GFP. Using frequency- and angle-resolved photoelectron spectroscopy, in combination with electronic structure theory, the onset of excited states that are responsible for the characteristic spectroscopic features in biochromophores are determined. A comprehensive, yet intuitive picture of the effect of phenolate functionalisation is developed based on simple Hückel theory. Specifically, the first two bright excited states can be constructed from a linear combination of molecular orbitals localised on the phenolate and para-substituent groups. This essential interaction is first observed for p-vinyl-phenolate. This bottom-up approach offers a readily accessible framework for the design of photoactive chromophores.

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发色团的生色团：自下而上的Hückel图片，显示光敏蛋白的激发态

许多光敏蛋白包含基于对位基团的发色团取代的酚盐阴离子是其电子结构的重要组成部分。在这里，我们提出了一种还原论方法，以从发色团的复杂性（从酚盐到GFP的复杂性）的增加，获得对电子结构演变的基本了解。使用频率和角度分辨光电子能谱，结合电子结构理论，可以确定引起生物发色团特征光谱特征的激发态的开始。基于简单的Hückel理论，得出了酚盐官能化作用的全面而直观的图景。具体来说，前两个明亮的激发态可以由位于酚盐和对位上的分子轨道的线性组合构成-取代基组。首先观察到对-乙烯基酚盐的这种基本相互作用。这种自下而上的方法为光敏发色团的设计提供了易于使用的框架。