Olsen Seth, McKenzie Ross H
Centre for Organic Photonics and Electronics and School of Mathematics and Physics, The University of Queensland, Brisbane QLD 4072 Australia.
J Chem Phys. 2009 May 14;130(18):184302. doi: 10.1063/1.3121324.
We give a quantum chemical description of the photoisomerization reaction of green fluorescent protein (GFP) chromophores using a representation over three diabatic states. Photoisomerization leads to nonradiative decay, and competes with fluorescence in these systems. In the protein, this pathway is suppressed, leading to fluorescence. Understanding the electronic states relevant to photoisomerization is a prerequisite to understanding how the protein suppresses it, and preserves the emitting state of the chromophore. We present a solution to the state-averaged complete active space problem, which is spanned at convergence by three fragment-localized orbitals. We generate the diabatic-state representation by block diagonalization transformation of the Hamiltonian calculated for the anionic chromophore model HBDI with multireference, multistate perturbation theory. The diabatic states are charge localized and admit a natural valence-bond interpretation. At planar geometries, the diabatic picture of the optical excitation reduces to the canonical two-state charge-transfer resonance of the anion. Extension to a three-state model is necessary to describe decay via two possible pathways associated with photoisomerization of the (methine) bridge. Parametric Hamiltonians based on the three-state ansatz can be fit directly to data generated using the underlying active space. We provide an illustrative example of such a parametric Hamiltonian.
我们使用基于三个非绝热态的表示方法，对绿色荧光蛋白（GFP）发色团的光异构化反应进行了量子化学描述。光异构化会导致非辐射衰变，并在这些体系中与荧光相互竞争。在蛋白质中，这条途径受到抑制，从而产生荧光。理解与光异构化相关的电子态是理解蛋白质如何抑制它并保持发色团发射态的先决条件。我们给出了态平均完全活性空间问题的一个解决方案，该问题在收敛时由三个片段定域轨道构成。我们通过用多参考、多态微扰理论对阴离子发色团模型HBDI计算得到的哈密顿量进行块对角化变换，生成了非绝热态表示。非绝热态是电荷定域的，并允许一种自然的价键解释。在平面几何构型下，光激发的非绝热图像简化为阴离子的典型双态电荷转移共振。扩展到三态模型对于描述通过与（次甲基）桥光异构化相关的两种可能途径的衰变是必要的。基于三态假设的参数化哈密顿量可以直接拟合到使用基础活性空间生成的数据。我们给出了这样一个参数化哈密顿量的一个示例。
