简并单次甲基染料极小模型中的锥交叉、电荷转移和光致异构化途径选择
Conical Intersections, Charge Transfer and Photoisomerization Pathway Selection in a Minimal Model of a Degenerate Monomethine Dye
摘要：
本文提出了一个单次甲基染料电子结构的极小模型哈密顿量，用以描述这类染料的光致异构化。该模型描述了三个非绝热电子态之间的相互作用，每个非绝热电子态都可以与价键结构相关联。单次甲基染料的特征在于电荷转移共振;由共振决定的单双键结构的不确定性反映在对应于不同次甲基键的光异构化途径的二元性中。衰变通道的可能多样性使环境对荧光量子产率的影响的机制模型以及相干控制策略复杂化。我们研究的程度和拓扑结构的交叉缝之间的电子状态的染料，以及它们如何涉及到不同的衰变途径之间的电荷本地化和选择。我们发现，S1和S 0表面之间的交叉点只发生大的扭曲角。相反，S2/S1交叉点可以发生在弗兰克-康登区域附近。当分子具有左右对称性时，所有的交叉点都与正旋转或反旋转有关，而从不与单键扭曲有关。对于不对称分子（即桥更强地耦合到一端），则S2和S1表面偏向不同键的扭转。电荷局域化和扭转路径偏置相关。我们将我们的观察与最近的几个实验和理论结果，这已经获得了类似结构的染料。
英文摘要：
We propose a minimal model Hamiltonian for the electronic structure of a monomethine dye, in order to describe the photoisomerization of such dyes. The model describes interactions between three diabatic electronic states, each of which can be associated with a valence bond structure. Monomethine dyes are characterized by a charge-transfer resonance; the indeterminacy of the single-double bonding structure dictated by the resonance is reflected in a duality of photoisomerization pathways corresponding to the different methine bonds. The possible multiplicity of decay channels complicates mechanistic models of the effect of the environment on fluorescent quantum yields, as well as coherent control strategies. We examine the extent and topology of intersection seams between the electronic states of the dye, and how they relate to charge localization and selection between different decay pathways. We find that intersections between the S1 and S0 surfaces only occur for large twist angles. In contrast, S2/S1 intersections can occur near the Franck-Condon region. When the molecule has left-right symmetry, all intersections are associated with con- or dis-rotations and never with single bond twists. For asymmetric molecules (i.e. where the bridge couples more strongly to one end) then the S2 and S1 surfaces bias torsion about different bonds. Charge localization and torsion pathway biasing are correlated. We relate our observations to several recent experimental and theoretical results, which have been obtained for dyes with similar structure.
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