Microsecond-resolved XAFS of the triplet excited state of Pt2(P2O5H2)4–4

Abstract
LITTLE is known about the excited-state structures of most inorganic compounds. Time-resolved resonance Raman and time-resolved infrared spectroscopies can provide only indirect structural information for short-lived excited species in solution at room temperature. Time-resolved X-ray diffraction1 has the potential to give more direct information, but no excited-state structures have yet been reported; picosecond gas-phase electron diffraction has been proposed recently2, but not yet demonstrated. Here we report a technique that combines the X-ray absorption fine-structure (XAFS) method3 with rapid-flow laser spectroscopy4 to measure structural changes in a solution-phase excited-state transition-metal complex with microsecond resolution. We find that the triplet excited state of Pt2(P2O5H2)4–4, with a lifetime of about 4 µs undergoes a contraction in the Pt–Pt distance of 0.52 ±0.13 Å relative to the ground state. We anticipate that time-resolved XAFS will have broad applications in chemistry and biology.

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