Photoinduced charge-transfer is an important process in nature and technology and is responsible for the emergence of exotic functionalities, such as magnetic order for cyanide-bridged bimetallic coordination networks. Despite its broad interest and intensive developments in chemistry and material sciences, the atomic-scale description of the initial photoinduced process, which couples intermetallic charge-transfer and spin transition, has been debated for decades; it has been beyond reach due to its extreme speed. Here we study this process in a prototype cyanide-bridged CoFe system by femtosecond X-ray and optical absorption spectroscopies, enabling the disentanglement of ultrafast electronic and structural dynamics. Our results demonstrate that it is the spin transition that occurs first on the Co site within ~50 fs, and it is this that drives the subsequent Fe-to-Co charge-transfer within ~200 fs. This study represents a step towards understanding and controlling charge-transfer-based functions using light.

光致电荷转移是自然界和技术中的一个重要过程，是产生奇异功能的原因，例如氰化物桥接双金属配位网络的磁序。尽管它在化学和材料科学领域有着广泛的兴趣和深入的发展，但对结合金属间电荷转移和自旋跃迁的初始光诱导过程的原子级描述已经争论了几十年。由于其极快的速度，它已经遥不可及。在这里，我们通过飞秒 X 射线和光学吸收光谱在原型氰化物桥接 CoFe 系统中研究这一过程，从而能够解开超快电子和结构动力学的纠缠。我们的结果表明，在~50 fs 内首先发生在 Co 位点的是自旋跃迁，正是这一点在~200 fs 内驱动了随后的 Fe-to-Co 电荷转移。这项研究代表了使用光理解和控制基于电荷转移的功能的一步。