Nature of the excited state of triangulo silver N-heterocyclic carbenes. Insights from relativistic DFT calculations.

Insights into the ground and excited states involved in the reported luminescent behavior of a complex involving the Ag(3) core stabilized by pyridil derivatives of N-heterocyclic carbenes has been achieved by means relativistic DFT calculations including scalar and spin-orbit coupling. The stabilization of the Ag(3) core is enhanced by the population of a highly symmetric bonding Ag(3) orbital, composed of 75% from the 5s, 15% from 5p, and 10% from 4d. Thus, stabilization of the Ag(3) core involves a slightly bonded d(10) metallic core in addition to the pure nonbonding argentophilic interaction picture. It is suggested that the population of this highly bonding Ag(3) orbital is responsible of the short Ag-Ag bond length observed in the studied compounds. The characterized electronic excitations allows to rule that the metal-ligand to ligand charge-transfer transitions account for the luminescent properties. The calculated Stokes shifts are in good agreement with the experimental data.