Metastable photoinduced phase of Cu(II) ethylenediamine complexes studied by x-ray-absorption fine-structure spectroscopy

Photoinduced phase transition of (formula presented) (formula presented)-diethylethlenediamine, (formula presented) and (formula presented) has been investigated by means of x-ray-absorption fine structure spectroscopy. Upon UV-light (formula presented) irradiation at 30 K, the materials undergo a photoinduced structural transition. Cu K-edge x-ray-absorption near-edge structure spectra have clarified that the initially planar (formula presented) unit is distorted tetrahedrally. Although the structural change within the first nearest neighbors around Cu is similar to that in the thermally driven transition (the high-temperature phase), the configuration of the surrounding ethyl and ethylene groups in the photoinduced phase was found to resemble that of the low-temperature phase rather than that of the high-temperature one. Namely, no noticeable reconstruction of ethyl groups takes place, which occurs in thermally activated transition. The photoinduced state is conclusively regarded as a new metastable state that is structurally not equivalent either to the high- or low-temperature phases.