Das Ankita, Mandal Imon, Venkatramani Ravindra, Dasgupta Jyotishman
Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India.
Sci Adv. 2019 Feb 22;5(2):eaav4806. doi: 10.1126/sciadv.aav4806. eCollection 2019 Feb.
Light energy absorbed by molecules can be harnessed to activate chemical bonds with extraordinary speed. However, excitation energy redistribution within various molecular degrees of freedom prohibits bond-selective chemistry. Inspired by enzymes, we devised a new photocatalytic scheme that preorganizes and polarizes target chemical bonds inside water-soluble cationic nanocavities to engineer selective functionalization. Specifically, we present a route to photoactivate weakly polarized sp C─H bonds in water via host-guest charge transfer and control its reactivity with aerial O. Electron-rich aromatic hydrocarbons self-organize inside redox complementary supramolecular cavities to form photoactivatable host-guest charge transfer complexes in water. An ultrafast C─H bond cleavage within ~10 to 400 ps is triggered by visible-light excitation, through a cage-assisted and solvent water-assisted proton-coupled electron transfer reaction. The confinement prolongs the lifetime of the carbon-centered radical to enable a facile yet selective reaction with molecular O leading to photocatalytic turnover of oxidized products in water.
分子吸收的光能可被用于以极快的速度激活化学键。然而，激发能在各种分子自由度内的重新分布阻碍了键选择性化学。受酶的启发，我们设计了一种新的光催化方案，该方案在水溶性阳离子纳米腔内对目标化学键进行预组织和极化，以实现选择性功能化。具体而言，我们提出了一条通过主客体电荷转移在水中光激活弱极化的sp C─H键并控制其与气态O反应活性的途径。富电子芳烃在氧化还原互补的超分子腔内自组装，在水中形成可光激活的主客体电荷转移复合物。通过笼辅助和溶剂水辅助的质子耦合电子转移反应，可见光激发在约10至400皮秒内触发超快的C─H键断裂。这种限制延长了以碳为中心的自由基的寿命，从而能够与分子O进行简便而选择性的反应，导致水中氧化产物的光催化周转。
