School of Mathematics and Physics, The University of Queensland, Brisbane QLD 4072 Australia.
J Phys Chem A. 2013 Mar 28;117(12):2455-68. doi: 10.1021/jp309006e. Epub 2013 Mar 18.
We offer a new physical interpretation of the color shift between diarylmethane dyes and their azomethine analogues. We use an isolobal analogy between state-averaged complete active space self-consistent field solutions for corresponding methines and azomethines to show that the shift contains a significant contribution from configuration interaction between a methine-like ππ* excitation and an nπ* excitation out of the azomethine lone pair. The latter does not exist in the corresponding methine systems. This picture is qualitatively inconsistent with traditional models of the shift based on molecular orbital perturbation theory of independent π-electron Hamiltonians. A key prediction is the existence of a dipole-allowed band in the blue/near-UV spectra of the azomethines, which has polarization parallel to the lowest energy band. This forces a revision of past assumptions about the nature of the low-energy spectra of the azomethines. A band at the predicted energies has been observed in solution-state spectra.
我们提供了一种新的物理解释，用于解释二芳基甲烷染料与其偶氮类似物之间的颜色位移。我们使用相应甲川和偶氮的状态平均完全活性空间自洽场解之间的等电子类比，表明位移包含甲川类似的 ππ激发和偶氮孤对的 nπ激发之间的组态相互作用的重要贡献。后者在相应的甲川体系中不存在。这种情况与基于独立π电子哈密顿量的分子轨道微扰理论的传统位移模型在定性上不一致。一个关键的预测是，在偶氮的蓝/近紫外光谱中存在一个偶极允许的带，其极化方向与最低能带平行。这迫使我们修正过去关于偶氮低能光谱性质的假设。在溶液状态的光谱中已经观察到预测能量的带。
