Application of XANES spectroscopy to study local structure of photoexcited Cu complex

A new technique for the analysis of transient X-ray absorption (also known as pump-and-probe XAS) and extraction of 3D structural information for photoexcited molecules is proposed. It is applied to metal-to-ligand-charge-transfer state of [Cu(dmp)2]+ (dmp=2,9-dimethyl-1,10-phenanthroline) in acetonitrile solution. Theoretical approach combines fitting of XANES spectra with a multidimensional interpolation approximation and calculating theoretical XANES with molecular potentials beyond the muffin-tin approximation. The results of the study show that the best fit of the experimental XANES data includes a solvent molecule binding to the Cu with Cu–N distance of 2.00 Å, average distance Cu–N of dmp groups is 2.04 Å and that photoexcited state is characterized by significant rocking distortions of the dmp ligands.