Department of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm, Sweden.
Phys Chem Chem Phys. 2011 Jul 21;13(27):12506-16. doi: 10.1039/c1cp20611g. Epub 2011 Jun 9.
The dimethylamino nitro stilbene (DANS) molecule is studied for exploring solvent effects on two-photon absorption using the quantum mechanical/molecular mechanical (QM/MM) response theory approach, where the quantum part is represented by density functional theory. We have explored the role of geometrical change of the chromophore in solution, the importance of taking a dynamical average over the sampled structures and the role of a granular representation of the polarization and electrostatic interactions with the classically described medium. The line shape function was simulated by the QM/MM technique thereby allowing for non-empirical prediction of the absolute two-photon cross section. We report a maximum in the TPA cross section for a medium of intermediate solvent polarity (i.e. in chloroform) and provide the grounds for an explanation of this effect which recently has been experimentally observed for a series of charge transfer species in solvents of different polarity. The calculations of absorption energies reproduce well the positive solvatochromic behavior of DANS and are in good agreement with experimental spectra available for the chloroform and DMSO solvents. In line with recent development of the QM/MM response technique for color modeling, we find this methodology to offer a versatile tool to predict and analyze two-photon absorption phenomena taking place within a medium.
二甲基氨基硝基芪（DANS）分子被研究用于探索使用量子力学/分子力学（QM/MM）响应理论方法的溶剂效应对双光子吸收的影响，其中量子部分由密度泛函理论表示。我们已经探索了在溶液中发色团的几何变化的作用，对采样结构进行动力学平均的重要性，以及用经典描述的介质来表示极化和静电相互作用的粒度的作用。线形状函数通过 QM/MM 技术进行了模拟，从而允许对绝对双光子截面进行非经验预测。我们报告了在中等溶剂极性（即在氯仿中）的介质中双光子吸收截面的最大值，并为最近在不同极性溶剂中一系列电荷转移物种中观察到的这种效应提供了解释的依据。吸收能的计算很好地再现了 DANS 的正溶剂化变色行为，并且与可用于氯仿和 DMSO 溶剂的实验光谱很好地吻合。与最近开发的用于颜色建模的 QM/MM 响应技术一致，我们发现这种方法为预测和分析在介质中发生的双光子吸收现象提供了一种通用工具。
