Chandra Sankhabrata, Bhattacharya Atanu
Department of Inorganic and Physical Chemistry, Indian Institute of Science , Bangalore, Karnataka, India 560012.
J Phys Chem A. 2016 Dec 29;120(51):10057-10071. doi: 10.1021/acs.jpca.6b09813. Epub 2016 Dec 2.
In general, charge migration can occur via pure electron-electron correlation and relaxation or via coupling with nuclear motion. We must understand both aspects of charge migration through the non-hydrogen noncovalent bonds to harness full potential of the halogen-, chalcogen-, pnicogen- and tetrel-bonded photosensitive functional materials. This feature article, however, is focused on the pure relaxation- and correlation-driven charge migration, subsequent charge localization, and finally on charge-directed reactivity in the non-hydrogen noncovalent bonded clusters. Pure relaxation- and correlation-driven charge migration can occur on a several hundred attosecond (as) time scale, and this is why chemical dynamics associated with this pure electronic charge migration can be named "attochemistry". One of the efficient ways to elucidate the attochemistry is via the vertical ionization by monitoring a nonstationary electronic charge density that evolves in time while the nuclear configuration remains unchanged. So far, attochemistry of several halogen-, chalcogen-, pnicogen-, and tetrel-bonded clusters has been studied theoretically by our group. All the interesting predictions have been summarized in this Feature Article. The time scales of relaxation- and correlation-driven charge migration through the halogen, chalcogen, pnicogen, and tetrel noncovalent bonds are found to be quite similar (approximately in the range of 300-600 as) in different (1:1) AX:NH and AX:OH complexes (where A represents different substituents, such as NH, CN, etc.). Basis sets do not exhibit any effect on the predicted charge migration time scale. A very long intermolecular distance (approximately more than 10 Å), for which (physically) no noncovalent bonding interaction can be present, ceases the intermolecular charge migration. The strength of the electron-electron correlation interaction influences the charge migration through these noncovalent bonds, making charge migration faster with a higher correlation interaction. The initial nuclear configuration affects the charge migration through the non-hydrogen noncovalent bonds. For large clusters, in which both hydrogen and non-hydrogen noncovalent bonds are formed, non-hydrogen noncovalent bonds are found to facilitate the charge migration preferentially over the hydrogen bonds. As a result of nuclear wavepacket delocalization, the attosecond charge oscillation in noncovalent bonded clusters decoheres. This renders charge localization. Subsequent charge-directed reactivity is discussed. This article is the first review on the attochemistry of non-hydrogen noncovalent bonded clusters.
一般来说，电荷迁移可以通过纯粹的电子 - 电子关联与弛豫或者通过与核运动的耦合来发生。我们必须了解通过非氢非共价键的电荷迁移的两个方面，以便充分发挥卤素、硫族、氮族和碳族键合的光敏功能材料的潜力。然而，这篇专题文章聚焦于纯粹由弛豫和关联驱动的电荷迁移、随后的电荷局域化，以及最终非氢非共价键合簇中的电荷导向反应性。纯粹由弛豫和关联驱动的电荷迁移可以在几百阿秒（as）的时间尺度上发生，这就是为什么与这种纯粹的电子电荷迁移相关的化学动力学可以被称为“阿秒化学”。阐明阿秒化学的有效方法之一是通过垂直电离来监测在核构型保持不变时随时间演化的非稳态电子电荷密度。到目前为止，我们小组已经从理论上研究了几种卤素、硫族、氮族和碳族键合簇的阿秒化学。所有有趣的预测都总结在这篇专题文章中。发现在不同的（1:1）AX:NH和AX:OH配合物（其中A代表不同的取代基，如NH、CN等）中，通过卤素、硫族、氮族和碳族非共价键的弛豫和关联驱动的电荷迁移的时间尺度非常相似（大约在300 - 600 as范围内）。基组对预测的电荷迁移时间尺度没有任何影响。非常长的分子间距离（大约超过10 Å），在这种情况下（从物理角度）不存在任何非共价键相互作用，会使分子间电荷迁移停止。电子 - 电子关联相互作用的强度会影响通过这些非共价键的电荷迁移，随着关联相互作用增强，电荷迁移会更快。初始核构型会影响通过非氢非共价键的电荷迁移。对于同时形成氢和非氢非共价键的大簇，发现非氢非共价键比氢键更有利于电荷迁移。由于核波包的离域，非共价键合簇中的阿秒电荷振荡会退相干。这导致电荷局域化。随后讨论了电荷导向反应性。本文是关于非氢非共价键合簇阿秒化学的第一篇综述。
