Time-Resolved X-ray Scattering of an Electronically Excited State in Solution. Structure of the 3A2u State of Tetrakis-μ-pyrophosphitodiplatinate(II)

The structure of the 3A2u excited state of tetrakis-μ-pyrophosphitodiplatinate(II) in aqueous solution is investigated by time-resolved X-ray scattering on a time scale from 100 ps to 1 μs after optical pumping. The primary structural parameter, the Pt−Pt distance, is found to be 2.74 A, which is 0.24 A shorter than the ground-state value. The contraction is in excellent agreement with earlier estimates based on spectroscopic data in solution and diffraction data in the crystalline state. As a second structural parameter, the distance between the P planes in the 3A2u excited state was determined to be 2.93 A, i.e., the same as that in the ground state. This result implies that a slight lengthening of the Pt−P bond occurs following excitation.