Electronic structure and adsorption geometry of Pt and Pd metal complexes with 1,3-dithiole-2-thione-4,5-dithiolate ligand on TiO2(101) surface from first-principles calculations

Metal complexes based on 1,3-dithiole-2-thione-4,5-dithiolate (dmit) ligand have been intensively studied for more than 40 years due to their unusual chemical and physical properties. Besides, the highly delocalized frontier orbitals, that allow direct electron transfer through the ligand π orbitals, make these class of complexes promising candidates for photochemical devices as well as sensitizer for dye-sensitized solar cells. In this work, we investigated the electronic and geometric properties of Pd and Pt (CH3)2[M(dmit)2] complexes isolated on TiO2(101) surface by means of first-principles calculations using plane-wave basis sets and DFT calculation. Adsorption energies of metal complexes supported on a TiO2(101) surface are calculated for three different configurations, linked by the sulfur atom of Sthione, Sthiole–Sthiolate, and planar. The studies found that the most stable adsorption molecular configuration mode for the palladium(II) and platinum(II) complexes is the planar mode. TD-DFT molecular calculations revealed that the lowest energy transition in the ultraviolet visible near-infrared range mainly corresponds to the HOMO–LUMO excitation for the (CH3)2[M(dmit)2] complexes. Theoretical calculations of optical absorption spectra of (CH3)2[M(dmit)2] complexes adsorbed on the anatase (101) surface show that the interaction induces a slightly redshift of electronic absorption bands. Density of states for the metal complexes/TiO2(101) system revealed that the LUMO of the metal complexes lies at below the edge of the TiO2 conduction band. The adsorption of the (CH3)2[Pd(dmit)2] complex on the anatase (101) surface results in the emergence of new transitions below 1 eV that can be ascribed to the presence of a favorable overlap between the LUMO of the complex and the conduction band of the TiO2 semiconductor.