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Time-resolved X-ray crystallography requires intense, short laser pulses to achieve ultrafast time resolution. It is currently not known to what extent double optical excitation as a result of intense laser illumination, can contribute to measured signals. We present a separation of weak and strong response from pump-probe data of photoactive yellow protein crystals collected at a single laser power, based on a method of indexing transformation followed by optical crystallography. We show that this allows precise separation of the heterogeneous photochemical populations with a very high level of data correlation that is intrinsic from the methodology of serial crystallography data collection. For a 3 ps pump-probe delay, the data shows evidence only for the trans-cis photoisomerisation reaction. Chromophore ionisation, which results from the double excitation in the strong response conditions, does not result in detectable crystallographic differences. The quantitative treatment of photoselection demonstrates that ultrafast time resolution can be established for single excitation dynamics of the functionally relevant photoisomerisation reaction of PYP [1].
1] Crystal optics select weak response of ultrafast crystallography. Perrett et al. ChemRxiv 2025 https://dx.doi.org/10.26434/chemrxiv-2025-72m69
| Scientific Topics | Chemistry |
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