ELECTRONIC STRUCTURE AND PHOTOCHEMISTRY OF INORGANIC PHOTOCHROMIC COMPLEX [Cu(N,N′-DIETHYLETHYLENEDIAMINE)₂]²⁺: PLANAR–TETRAHEDRAL GEOMETRY CHANGE ACCOMPANIED WITH d⁹–d¹⁰ ELECTRONIC TRANSITION

A photo-induced geometry isomerization reaction mechanism of a photochromic inorganic complex, [Cu(dieten)₂]²⁺ (dieten = N,N′-diethyletylenediamine), was investigated with density functional molecular orbital theory calculations. A new stable cis-isomer that is assigned to a photo-irradiated (PI) phase was found. In the PI geometry, two N,N′-diethyl groups are placed more closely than in the most stable low-temperature (LT) phase, and the complex has a slightly twisted structure with steric hindrance. Recently, Takahashi et al. have suggested that two ethyl groups were in trans position in the PI phase from the EXAFS and XANES observation; however, no energy minimum corresponds to such a PI state was found. The photochromic reaction mechanism and electronic structure of [Cu^II(dieten)₂]²⁺ are discussed from a theoretical point of view.