A single-crystal platform for unveiling ultrafast and complex photochemical cascade reactions

Developing versatile crystalline platforms can significantly enhance the utility of time-resolved X-ray crystallography for observing diverse reaction mechanisms ^{1–6 . However, it is often limited by its inability to handle ultrafast and complex reactions. Here we propose a coordination polymer single-crystal platform that incorporates flexible cluster nodes and integrated reaction substrates. This advanced platform features enhanced diffraction capabilities and adaptability to substrate changes, enabling the observation of ultrafast, highly dynamic reactions involving multiple pathways and intermediates. By combining this platform with a cryo-assisted strategy, we investigate a complicated ultrafast photochemical cycloaddition reaction with five transient intermediates and three distinct routes, which are rationalized through theoretical calculations. Our findings underscore the feasibility of employing this enhanced single-crystal platform to unravel elusive reaction mechanisms, presenting a promising approach with broad applicability.}