Internal conversion (IC) is a common radiationless transition in polyatomic molecules. Theory predicts that molecular vibrations assist IC between excited states, and ultrafast experiments can provide insight into their structure–function relationship. Here we elucidate the dynamics of the vibrational modes driving the IC process within the Q band of a functionalized porphyrin molecule. Through a combination of ultrafast multidimensional spectroscopies and theoretical modeling, we observe a 60 fs Q_y–Q_x IC and demonstrate that it is driven by the interplay among multiple high-frequency modes. Notably, we identify 1510 cm^–1 as the leading tuning mode that brings the porphyrin to an optimal geometry for energy surface crossing. By employing coherent wave packet analysis, we highlight a set of short-lived vibrations (1200–1400 cm^–1), promoting the IC within ≈60 fs. Furthermore, we identify one coupling mode (1350 cm^–1) that is responsible for vibronic mixing within the Q states. Our findings indicate that porphyrin-core functionalization modulates IC effectively, offering new opportunities in photocatalysis and optoelectronics.

中文翻译：

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电子振动耦合驱动功能化游离碱卟啉的超快内部转换

内转换（IC）是多原子分子中常见的无辐射跃迁。理论预测分子振动有助于激发态之间的 IC，超快实验可以深入了解它们的结构-功能关系。在这里，我们阐明了驱动功能化卟啉分子 Q 带内 IC 过程的振动模式的动力学。通过超快多维光谱和理论建模的结合，我们观察到了 60 fs Q _y –Q _x IC，并证明它是由多个高频模式之间的相互作用驱动的。值得注意的是，我们确定 1510 cm ^–1是主要的调谐模式，它使卟啉达到能量表面交叉的最佳几何形状。通过采用相干波包分析，我们突出了一组短暂的振动 (1200–1400 cm ^–1 )，将 IC 提升到约 60 fs 内。此外，我们确定了一种耦合模式 (1350 cm ^–1 )，它负责 Q 态内的振动混合。我们的研究结果表明，卟啉核心功能化可以有效地调节 IC，为光催化和光电子学提供了新的机遇。