Light-induced excited state X-ray crystallography of multinuclear copper complexes

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Multinuclear Cu(I) complexes such as [Cul(py)]4 have shown luminescent by UV light irradiation. In the photoexcited states, distortion of metal cluster core has been expected. To observe this molecular distortion in the photoexcited states directly by single crystal X-ray diffraction analyses, we have performed development of a diffractometer, establishment of excited states structure refinement calculations, and survey of target compounds. Light illuminating devices has been installed in the "low-temperature vacuum X-ray camera" which are designed for obtaining low noise diffraction images at low temperature. The multiple-exposure image plate (IP) method is a new detection technique developed in this project and installed in this camera, by which both diffraction patterns measured for light irradiated and non-irradiated conditions are recorded on the same IP. The X-ray camera has settled in a Spring-8 beamline utilizing highbrilliant X-ray radiation sources. Molecular distortion in the light irradiated crystal can be detected by a differential Fourier syntheses using X-ray diffraction intensity changes between light-on and off conditions, followed by qualitative calculation of excited state population and geometrical changes in a crystal, using least square refinements. Structure analysis of a luminescent a diplatinum(II) complex (Bu_4N)_2H_2[Pt_2(pop)_4] single crystal under blue laser irradiation has been successfully performed. Photoexcited molecule of 1.4% population shows Pt-Pt bond shrinkage of 0.23 A under blue laser irradiation which is consistent with spectroscopic investigations.