Theoretical and experimental methodologies that can characterize electronic and nuclear dynamics, and the coupling between the two, are needed to understand photoinduced charge transfer in molecular building blocks used in organic photovoltaics. Ongoing developments in ultrafast pump-probe techniques such as time-resolved X-ray absorption spectroscopy, using an X-ray free electron laser in combination with an ultraviolet femtosecond laser, present desirable probes of coupled electronic and nuclear dynamics. In this work, we investigate the charge transfer dynamics of a donor-acceptor pair, which is widely used as a building block in low bandgap block copolymers for organic photovoltaics. We simulate the dynamics of the benzothiadiazole-thiophene molecule upon photoionization with a vacuum ultraviolet (VUV) pulse and study the potential of probing the subsequent charge dynamics using time-resolved X-ray absorption spectroscopy. The photoinduced dynamics are calculated using on-the-fly nonadiabatic molecular dynamics simulations based on Tully's Fewest Switches Surface Hopping approach. We calculate the X-ray absorption spectrum as a function of time after ionization at the Hartree-Fock level. The changes in the time-resolved X-ray absorption spectrum at the sulfur K-edge reveal the ultrafast charge carrier dynamics in the molecule occurring on a femtosecond time scale. These theoretical findings anticipate that ultrafast time-resolved X-ray absorption spectroscopy using an X-ray probe in combination with a VUV pump offers a new approach to investigate the detailed dynamics of organic photovoltaic materials.

中文翻译：

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通过模拟的时间分辨X射线吸收光谱揭示了光伏供体-受体对中的空穴动力学。

需要能够表征电子和核动力学以及两者之间的耦合的理论和实验方法，以了解有机光伏中使用的分子构件中的光诱导电荷转移。超快泵浦探测技术的不断发展，例如时间分辨X射线吸收光谱，结合使用X射线自由电子激光器和紫外飞秒激光器，提出了耦合电子和核动力学的理想探针。在这项工作中，我们研究了供体-受体对的电荷转移动力学，该对被广泛用作有机光伏低带隙嵌段共聚物的结构单元。我们模拟了真空紫外线（VUV）脉冲在光电离后苯并噻二唑-噻吩分子的动力学，并研究了使用时间分辨X射线吸收光谱探测随后的电荷动力学的潜力。使用基于Tully的Fewest Switches Surface Hopping方法的动态非绝热分子动力学模拟计算光诱导动力学。我们在Hartree-Fock级电离后计算X射线吸收光谱随时间的变化。硫K边缘的时间分辨X射线吸收谱的变化揭示了飞秒级的分子中超快电荷载流子动力学。