Self-Assembly of Mechanoluminochromic Ladder-Shaped Gold(I) Clusters Promoted Using Cooperative Aurophilicity

Abstract

The self-assembly of mechanoluminochromic polynuclear gold­(I) complexes has attracted more and more attention in the field of supramolecular gold­(I) chemistry. In this work, we adopted a stepwise self-assembly strategy to precisely synthesize two polynuclear gold­(I) supramolecular clusters. Through cooperative AuI···AuI and Au–N interactions, the gold­(I) clusters 1 +•BF4 – and 2 4+•4BF4 – with Au4 and Au16 cores, respectively, were successfully constructed. In these supramolecular clusters, (dppm)­Au2Cl2 coordination motifs and trithiocyanuric linkers were stepwise assembled via sequential thiolate–chloride/phosphine coordination substitution and Au–S/Au–N coordination bond rearrangement. Two well-defined gold­(I) supramolecular clusters displayed intense emission both in the solid state and in solution. Furthermore, the ladder-shaped cluster 2 4+•4BF4 – exhibited reversible mechanochromic luminescence behavior in the solid state as well as aggregation-caused redshifted emission in solution. Upon mechanical grinding, the emission of the cluster 2 4+•4BF4 – changed from yellow at 582 nm to red at 612 nm. The initial emission could be fully recovered by treatment with acetonitrile.

Self-Assembly and Mechanochromism Behavior of Gold(I) Supramolecular Cluster

“…380 nm was gradually enhanced (Figure a). As shown in Figure S15, the absorption plot at 380 nm as a function of the complex concentration exhibited a nonlinear relationship, suggesting that ladder cluster 1 2+ ·2BF 4 – was likely to self-aggregate into a higher oligomer. − Meanwhile, the emission of cluster 1 2+ ·2BF 4 – in MeCN solution was concentration-dependent due to the aggregation, and the emission intensity increased exponentially when the concentration reached 3.13 × 10 –5 M (Figure d). In order to get insight into the intermolecular aggregation behavior in solution, the concentration-dependent electronic absorption spectra of cluster 1 2+ ·2BF 4 – in acetonitrile solution were measured at room temperature (Figures a and S15).…”

“…The electron spray ionization–mass spectroscopy (ESI-MS) spectra of 1 2+ ·2BF 4 – in acetonitrile showed two domain peaks corresponding to that of consecutive loss of Cl – counterions (Figure S6). The mass-to-charge ratio ( m / z ) of [ 1 -Cl – ] 3+ and [ 1 ] 2+ fragments peaked at 2063.29 and 3112.44, respectively, suggesting that the folding structure was partially maintained in solution …”

“…The high-energy absorption band at ca. 266 nm (ε max = 77,080 M –1 cm –1 ) indicated the metal-perturbed intraligand charge transfer of the triazine trithiolate linkers, − ,− and the low-energy absorption at ca. 319 nm (ε max = 69,680 M –1 cm –1 ) was tentatively assigned to ligand-to-metal charge transfer (thiolate-to-gold).…”

“…− has been reported in previous work. 30 These results suggested that cluster 2 + served as the primary assembly precursor to ladder clusters (Figure 3a). After reaction for 3 h, molecular ion peaks of m/z = 1197.13 (+1) and 1962.02 (+1) attributed to Int 3 and Int 2-dppmAuCl (Au 5 + ) were identified, respectively (Figures 2d and S12d).…”

“…30 After Au−Cl was completely replaced with Au−S/N bonds, a high nuclear ladder-shaped cluster Au 16 with a strong aurophilicity motif with excellent mechanoluminochromic properties was self-assembled. 30 Inspired by this work, we developed a stoichiometric controlling synthetic method to precisely construct a gold(I) cluster with Au−Cl bonds partially substituted by trithiocyanuric ligand (tatt 3− ) as a ditopic linker and diphosphine-supported dinuclear (dppm)Au 2 Cl 2 as a secondary building unit (Scheme 1). In this strategy, the N and S coordination sites of the ditopic ligand can be sequentially triggered with the increase in the stoichiometric amount of dppmAu 2 Cl 2 , resulting in aurophilic-driven conformation rearrangement.…”