Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
J Phys Chem Lett. 2021 Oct 7;12(39):9493-9500. doi: 10.1021/acs.jpclett.1c02353. Epub 2021 Sep 24.
Multiphoton excitation promises opportunities for opening new photochemical reaction pathways and controlling photoproduct distributions. We demonstrate photonic control of the 6π photocyclization of -terphenyl to make 4,4-dihydrotriphenylene (DHT). Using pump-repump-probe spectroscopy we show that 1 + 1' excitation to a high-lying reactant electronic state generates a metastable species characterized by a red absorption feature that accompanies a repump-induced depletion in the one-photon -dihydro product (-DHT); signatures of the new photoproduct are clearer for a structural analogue of the reactant that is sterically inhibited against one-photon cyclization. Quantum-chemical computations support assignment of this species to -DHT, which is accessible photochemically along a disrotatory coordinate from high-lying electronic states reached by 1 + 1' excitation. We use time-resolved spectroscopy to track photochemical dynamics producing -DHT. In total, we demonstrate that selective multiphoton excitation opens a new photoreaction channel in these photocyclizing reactants by taking advantage of state-dependent correlations between reactant and product electronic states.
多光子激发有望为开辟新的光化学反应途径和控制光产物分布提供机会。我们展示了通过光子控制来实现-terphenyl 的 6π 光环化，生成 4,4-二氢三联苯（DHT）。通过泵浦-重泵-探测光谱学，我们表明，激发到高能反应物电子态的 1 + 1'激发产生了一种亚稳态物质，其特征是吸收特征红移，伴随着重泵诱导的单光子 -二氢产物（-DHT）耗尽；对于反应物的结构类似物，新产物的特征更为明显，因为该类似物受到单光子环化的空间位阻抑制。量子化学计算支持将这种物质分配给-DHT，它可以通过 1 + 1'激发到达的高能电子态的反式旋转坐标光化学途径获得。我们使用时间分辨光谱学来跟踪产生-DHT 的光化学反应动力学。总的来说，我们证明了通过利用反应物和产物电子态之间的状态相关相关性，选择性多光子激发为这些光环化反应物开辟了新的光反应通道。
