Photophysical and DFT Studies of Cationic Ag(I) Complexes with Thiosemicarbazides Derived from p-Toluenesulfohydrazide

Reactions of p-toluenesulfohydrazide with R-isothiocyanates afford new ligands containing both the sulfonamide and thiosemicarbazide moieties (L-R: R=cyclohexyl (Cy) or phenyl (Ph)). L-R reacts with AgNO3 in EtOH in a 2:1M ratio leading to formation of colourless Ag(I) complexes of general formula [Ag(L-R)(2)]NO3. The crystal structure of a representative complex was determined by crystallographic studies and shows the Ag(I) coordinated by two thiosemicarbazide ligands in a S-monodentate coordination mode along with a significant interaction with a nitrate counter-ion in a bent geometry. Photophysical studies show that both the free ligands and complexes are essentially non-luminescent at room temperature. At 77K and glassy media, the silver complexes exhibit a luminescence band in the visible-light region. Besides, experimental and theoretical analyses suggest the population of the triplet state of these complexes after electronic excitation at around 250nm. Overall, it was verified that the observed emission of the Ag(I) complexes can be attributed to (MLCT)-M-3 radiative decay and that the silver complex with L-Ph shows a higher intensity emission than the complex with L-Cy.