Structural Study of Photo-Induced Phenomena in Crystals by Synchrotron Radiation Crystallography

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In order to reveal the photo-induced small structural changes using the single crystal structure analyses, it has been understood that the rise in heat of the crystal specimen according to the light irradiation should be a significant problem. We succeeded in the suppression of the crystal heating less than 0.1K by introducing the new timesharing IP multiple exposure method, in which incident X-ray and excitation light was intermitted synchronously by using a couple of rotary choppers.Photo-excited structure analysis was applied to the luminescent dicopper(I) complexes [Cu_2I_2(PPh_3)_2(4,4'-bpy)]_∞, which consist of {Cu_2I_2 } planer units bridged by diimine ligands constructing infinite chain structures. Single crystal X-ray diffraction experiments under photo-illumination were performed at 40 K by using the low-temperature vacuum X-ray camera at SPring-8 BL02B1 beamline. Two set of reflection data of intensity changes owing to light irradiation were measured by the timesharing IP mu … More ltiple exposure method under two laser light of wavelengths on the absorption band (442 nm) and on its tail (532 nm). Photo-difference Fourier syntheses for the 442 nm irradiation data show significant positive and negative peaks around Cu and I atoms, though that for the 532 nm data show no significant peak. The least-squares refinement based on the photo-induced intensity changes revealed that ca. 1.1% of the Cu and I atoms moved and resulted in the shortening of the Cu-I bond and I...I distance of 0.2Å and 0.6Å, respectively.Crystal structure analysis of the photo-induced nitrene has been determined successfully by using the host-guest complex of [(PhCH_2)_2NH_2]^+[m-C_6H_4(N_3)(COO)]^-. The intensity data were collected at 25 K using the low-temperature vacuum X-ray camera at SPring-8 before and after UV-irradiation with a high-pressure mercury lamp. It has been revealed that ca. 7% of the triplet nitrene and the isolated nitrogen molecule were generated and the C-N bond distance in the triplet nitrene was 1.34(4)Å. Less