Single-molecule spectroscopy aims to unveil often hidden but potentially very important contributions of single entities to a system’s ensemble response. Albeit contributing tremendously to our ever growing understanding of molecular processes, the fundamental question of temporal evolution, or change, has thus far been inaccessible, thus painting a static picture of a dynamic world. Here, we finally resolve this dilemma by performing ultrafast time-resolved transient spectroscopy on a single molecule. By tracing the femtosecond evolution of excited electronic state spectra of single molecules over hundreds of nanometres of bandwidth at room temperature, we reveal their nonlinear ultrafast response in an effective three-pulse scheme with fluorescence detection. A first excitation pulse is followed by a phase-locked de-excitation pulse pair, providing spectral encoding with 25 fs temporal resolution. This experimental realization of true single-molecule transient spectroscopy demonstrates that two-dimensional electronic spectroscopy of single molecules is experimentally within reach.

单分子光谱学的目的是揭示单个实体对系统整体响应的经常隐藏但可能非常重要的贡献。尽管对我们对分子过程的不断增长的理解做出了巨大贡献，但是迄今为止，时间演化或变化的根本问题仍然无法解决，从而描绘了动态世界的静态画面。在这里，我们最终通过对单个分子执行超快速时间分辨瞬态光谱法解决了这一难题。通过追踪在室温下数百纳米带宽下单分子的激发电子状态光谱的飞秒演化，我们在有效的三脉冲方案中通过荧光检测揭示了它们的非线性超快响应。在第一个激励脉冲之后是锁相去激励脉冲对，提供具有25 fs时间分辨率的频谱编码。真正的单分子瞬态光谱学的这一实验实现证明，单分子的二维电子光谱学在实验上是可以达到的。