Huang-Fu Zhi-Chao, Qian Yuqin, Deng Gang-Hua, Zhang Tong, Schmidt Sydney, Brown Jesse, Rao Yi
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States.
ACS Phys Chem Au. 2023 Apr 25;3(4):374-385. doi: 10.1021/acsphyschemau.3c00011. eCollection 2023 Jul 26.
Many photoinduced excited states' relaxation processes and chemical reactions occur at interfaces and surfaces, including charge transfer, energy transfer, proton transfer, proton-coupled electron transfer, configurational dynamics, conical intersections, etc. Of them, interactions of electronic and vibrational motions, namely, vibronic couplings, are the main determining factors for the relaxation processes or reaction pathways. However, time-resolved electronic-vibrational spectroscopy for interfaces and surfaces is lacking. Here we develop interface/surface-specific two-dimensional electronic-vibrational sum frequency generation spectroscopy (2D-EVSFG) for time-dependent vibronic coupling of excited states at interfaces and surfaces. We further demonstrate the fourth-order technique by investigating vibronic coupling, solvent correlation, and time evolution of the coupling for photoexcited interface-active molecules, crystal violet (CV), at the air/water interface as an example. The two vibronic absorption peaks for CV molecules at the interface from the 2D-EVSFG experiments were found to be more prominent than their counterparts in bulk from 2D-EV. Quantitative analysis of the vibronic peaks in 2D-EVSFG suggested that a non-Condon process participates in the photoexcitation of CV at the interface. We further reveal vibrational solvent coupling for the zeroth level on the electronic state with respect to that on the ground state, which is directly related to the magnitude of its change in solvent reorganization energy. The change in the solvent reorganization energy at the interface is much smaller than that in bulk methanol. Time-dependent center line slopes (CLSs) of 2D-EVSFG also showed that kinetic behaviors of CV at the air/water interface are significantly different from those in bulk methanol. Our ultrafast 2D-EVSFG experiments not only offer vibrational information on both excited states and the ground state as compared with the traditional doubly resonant sum frequency generation and electronic-vibrational coupling but also provide vibronic coupling, dynamical solvent effects, and time evolution of vibronic coupling at interfaces.
许多光致激发态的弛豫过程和化学反应发生在界面和表面，包括电荷转移、能量转移、质子转移、质子耦合电子转移、构型动力学、锥形交叉等。其中，电子和振动运动的相互作用，即振动电子耦合，是弛豫过程或反应路径的主要决定因素。然而，缺乏针对界面和表面的时间分辨电子-振动光谱。在此，我们开发了界面/表面特异性二维电子-振动和频光谱（2D-EVSFG），用于研究界面和表面激发态的时间相关振动电子耦合。我们以空气/水界面的光激发界面活性分子结晶紫（CV）为例，通过研究其振动电子耦合、溶剂相关性和耦合的时间演化，进一步展示了这种四阶技术。2D-EVSFG实验发现，界面处CV分子的两个振动电子吸收峰比二维电子振动光谱（2D-EV）中本体中的对应峰更显著。对2D-EVSFG中振动电子峰的定量分析表明，非康登过程参与了CV在界面处的光激发。我们进一步揭示了电子态零级相对于基态的振动溶剂耦合，这与溶剂重组能变化的大小直接相关。界面处溶剂重组能的变化远小于本体甲醇中的变化。2D-EVSFG的时间相关中心线斜率（CLS）也表明，CV在空气/水界面的动力学行为与本体甲醇中的显著不同。我们的超快2D-EVSFG实验不仅与传统的双共振和频光谱及电子-振动耦合相比，提供了激发态和基态的振动信息，还提供了界面处的振动电子耦合、动态溶剂效应以及振动电子耦合的时间演化。
