Dipartimento di Chimica e Chimica Industriale, University of Pisa , Via G. Moruzzi 13, 56124 Pisa, Italy.
Institut für Theoretische Chemie, Universität Wien , Währinger Strasse 17, A-1090 Wien, Austria.
J Chem Theory Comput. 2017 Aug 8;13(8):3778-3786. doi: 10.1021/acs.jctc.7b00475. Epub 2017 Jul 27.
Charge and structural relaxation of electronically excited states in embedded systems are strongly affected by the environment. It is known that the largest part of environment effects comes from electrostatics. However, polarization can also play a role by tuning the electronic and geometrical properties of the states, finally modifying the fluorescence. Here we present the formulation of analytical excited-state gradients within a polarizable QM/MM approach and their implementation within the ONIOM framework. A time-dependent DFT level of theory is used in combination with an induced dipole formulation of the polarizable embedding. The formation and relaxation of the bright excited state of an organic dye (DAPI) intercalated in a DNA pocket is used to quantify the role played by the mutual polarization between the QM subsystem and the embedding and also to investigate the onset of overpolarization, which is a known limit of the model with potentially detrimental effects. On the one hand, the results indicate the robustness of the QM-classical interface and, on the other hand, show the non-negligible effect of polarization between DAPI and a DNA pocket in determining the fluorescence properties of the embedded dye.
嵌入系统中电子激发态的电荷和结构弛豫受到环境的强烈影响。已知环境效应的最大部分来自静电。然而，通过调整状态的电子和几何性质，极化也可以发挥作用，最终改变荧光。在这里，我们提出了在极化 QM/MM 方法内的分析激发态梯度的公式及其在 ONIOM 框架内的实现。使用时变密度泛函理论与极化嵌入的感应偶极子公式相结合。将有机染料（DAPI）嵌入 DNA 口袋中的亮激发态的形成和弛豫用于量化 QM 子系统和嵌入之间的相互极化所起的作用，以及研究过极化的开始，这是模型的已知限制，具有潜在的有害影响。一方面，结果表明 QM-经典界面的稳健性，另一方面，表明 DAPI 和 DNA 口袋之间的极化对确定嵌入染料的荧光性质有不可忽视的影响。
