Circular dichroism of transition metal complexes within time-dependent density functional theory

Despite the fact that molecular circular dichroism (CD) was first observed in the visible absorption bands of transition metal complexes, optical activity of chiral coordination compounds is far less understood than that of organic molecules, due to the complexity of the electronic structures and transitions involved. Theoretical methods can help greatly in the assignment and interpretation of CD spectra for such molecules. However, first principle quantum-mechanical computation of the chiroptical properties is often a challenge for ab initio wavefunction-based methods. Time-dependent density functional theory (TO-OFT) due to its high efficiency is enjoying enormous popularity as the premier approach to dealing with these properties.;In the present work, a TO-OFT method has been employed to investigate the electronic structures and electronic CD spectra of typical transition metal complexes. The systems under consideration involve different types of ligands and metal ions, and the CD of interest arises from electronic transitions of various characters. The simulated CD spectra are compared with the experiment data wherever available and the CD spectra as well as electronic structures are analyzed in detail. In some cases, the theoretical results serve as a tool for elucidating the absolute configuration of the complexes, by pointing to transitions for which the sign of the rotatory strength can be used as fingerprint for one particular configuration. Moreover, much effort has been devoted to the elucidation of the mechanism by which typical transitions in the metal complexes acquire their CD intensity, and to the interpretation of the relationship between molecular structures and the corresponding optical activity.