Different phosphorescent excited states of tetra- and octanuclear dendritic-like phosphine gold(i) thiolate complexes: photophysical and theoretical studies

Abstract

The study of the photophysical properties of dendritic-like phosphinothiolate gold(I) complexes has been carried out. The studied complexes are two series of analogous compounds bearing 4 or 8 metal centers: the tetranuclear [Au₄(S-C₆H₄-X)₄{DAB-G0-(PPh₂)₄}] (X = F (3), MeO (4), Me (5) and NO₂ (6)) and the octanuclear [Au₈(S-C₆H₄-X)₈{DAB-G1-(PPh₂)₈}] (X = F (9), MeO (10), Me (11) and NO₂ (12)) complexes. All compounds are brightly luminescent in solid state at 77 K displaying lifetimes in the microsecond range. The correlation between the substituent in position four of the benzenethiolate ligand and the emission energy shows that the emissions arise from ³[pπ(S)→pσ(Au)] or from intra-ligand ³[π(S)→π*(C₆H₄X)] charge transfer transitions, depending on the substituents. Theoretical DFT-B3LYP, ONIOM (DFT-B3LYP/UFF) and ONIOM (MP2/UFF) calculations on mononuclear and dinuclear model systems permit evaluation of both the structural distortions upon excitation to the lowest triplet excited state T₁ and the shape of the orbitals involved in the charge transfer transitions. These calculations also allow us to evaluate the influence of the substituent in position four of the benzenethiolate ligand and the presence of Au⋯Au interactions.