Time-Dependent Molecular Rearrangement of [Au(N9-adeninate)(PTA)] in Aqueous Solution and Aggregation-Induced Emission in a Hydrogel Matrix

Dynamic Motions of Ligands around the Metal Centers Afford a Fidget Spinner-Type AIE Luminogen

A new type of aggregation-induced emission (AIE) luminogen containing a dimeric metal fragment and two or three phthalazine ligands is described, which shows dynamic motions of ligands around the metal centers in solution. Based on the variable-temperature and EXSY NMR spectroscopy data, X-ray crystallography structures, and computational results, three different pathways (i.e., reversible exchange with haptotropic shifts, circulation of ligands around the dimeric metal fragment, and walking on the spot of ligands on the metal centers) were considered for this dynamic behavior. Restriction of these dynamic processes in the aggregate forms of the compounds (in H2O/CH3CN solvent mixtures) contributes to their AIE. DFT calculations and NMR analysis showed that bright excited states for these molecules are not localized on isolated molecules, and the emission of them stemmed from π-dimers or π-oligomers. The morphologies and the mode of associations in the solvent mixtures were determined by using transmission electron microscopy (TEM) and concentration-dependent NMR spectroscopy. The computational results showed the presence of a conical intersection (CI) between the S0 and S1 excited state, which provides an accessible pathway for nonradiative decay in these systems.

Spontaneous Water-Promoted Self-Aggregation of a Hydrophilic Gold(I) Complex Due to Ligand Sphere Rearrangement

Aggregating gold(I) complexes in solution through short aurophilic contacts promotes new photoluminescent deactivation pathways (aggregation-induced emission, AIE). The time dependence of spontaneous AIE is seldom studied. We examine the behavior of complex [Au(N9-hypoxanthinate)(PTA)] (1) in an aqueous solution with the aid of variable-temperature NMR, time-resolved UV-Vis and photoluminescence spectroscopy, and PGSE NMR. The studies suggest that partial ligand scrambling in favor of the ionic [Au(PTA)2][Au(N9-hypoxanthinate)2] pair followed by anion oligomerization takes place. The results are rationalized with the aid of computational calculations at the TD-DFT level of theory and IRI analysis of the electron density.

Spontaneous in situ generation of photoemissive aurophilic oligomers in water solution based on the 2-thiocytosine ligand

Complexes [Au(S-2-thiocytosinate)(PMe₃)] (2, 2-thiocytosine = 4-amino-2-mercaptopyrimidine) and [Au(S-2-thiocytosine)(PMe₃)](CF₃CO₂) (3) have been prepared by the reaction of [Au(acac)(PMe₃)] (1, acac = acetylacetonate) or [Au(OCOCF₃)(PMe₃)] with 2-thiocytosine, respectively. The equimolecular mixture of complexes 1 and 3 also produces [{Au(PMe₃)}₂(μ-S,N¹-2-thiocytosinate)](CF₃CO₂) (4), which features two distinct [Au(PMe₃)]⁺ groups coordinated to the S and N¹ atoms of the heterocycle. Complex 4 experiences a ligand redistribution process in water solution that liberates [Au(PMe₃)₂](CF₃CO₂) and a brightly coloured and luminescent species of [Au_n(μ-S,N¹-2-thiocytosinate)_n] stoichiometry, presumably as a tetraauracycle (n = 4).

The doubly-aurated [{Au(PMe₃)}₂(μ-S,N¹-2-thiocytosinate)]⁺ cation breaks up in water solution to form a strongly-coloured and photoluminescent neutral aurophilic oligomer.

Multidisciplinary study on the hydrogelation of the digold(i) complex [{Au(9N-adeninate)}2(μ-dmpe)]: optical, rheological, and quasi-elastic neutron scattering perspectives

Non-conventional experimental techniques such as rheology or QENS will aid synthetic inorganic chemists to broaden the knowledge on gold(i) hydrometallogels’ structure and properties and to understand their expected relationship.