Identifying of charge-transfer transitions and reactive centers in M(diimine)(dithiolate) complexes by DFT techniques

This review is focused on theoretical aspects of mixed diimine–dithiolate complexes by means of DFT and TD-DFT methods. Thus, the geometry, the character of charge-transfer transitions and excited states in a series of M(diimine)(dithiolate), where M = Ni, Pd and Pt, is examined by DFT and TD-DFT techniques combined with polarized continuum model. The theoretical calculations reveal not only the role of the ligands – namely diimine and dithiolato and their substituents – but also the role of the metal in the excited triplet and singlet states and as a consequence in the properties of these complexes (electronic and photophysics) and their potential use as photosensitizers, NLO materials, light energy conversion materials and biological agents. The calculated energies of the lowest triplet and singlet state in all these complexes are in good agreement with absorption spectra and luminescence studies—where they are available. The contribution of the metal in the chemical and photophysics properties of this class of compounds is also demonstrated by two indices derived by DFT techniques: NICS (for chemical) and Fukui functions (for chemical and photophysical properties). The former acts as a meter of the delocalization of these molecules whereas the latter identifies the reactive centres of the molecule. All the theoretical results are in accordance with the experimental ones—geometrical structures, absorption, luminescence and 1H NMR spectra as well as products of given reactions, indicating the applicability of the DFT and TD-DFT techniques in examining the properties of metal coordinated complexes especially in a series of the same class of compounds.