Thermal/Redox-triggered release of pyrazinic functional molecules by coordination polymers with luminescence monitoring ability.

Storage of volatile active molecules, along with the prolongation of their specific functions, requires the use of regulatable carriers. Pyrazine derivatives are highly volatile compounds with a broad application owing to their flavoring, pharmaceutical, antimicrobial, antiseptic, and insecticidal properties. In this study, pyrazines were stored by coordinating them with cuprous iodide to easily generate a series of luminescent coordination polymer (CP)-based carriers. The CPs could respond to thermal-redox stimuli and manipulate pyrazine release by breaking the labile Cu-N bonds when triggered by the two stimuli. Moreover, the release process could be visualized by decreased luminescence caused by the gradual decomposition of CP structures. The loading efficiencies ranged from 31% to 38%, and the controlled release behaviors accord with the zero-order kinetics. This work is the first to prove that CPs could function as dual stimuli-mediated delivery systems, which hold the potential to control the release and strengthen the usability of functional molecules.

Achiral-Core-Metal Change in Isomorphic Enantiomeric Ag12Ag32 and Au12Ag32 Clusters Triggers Circularly Polarized Phosphorescence.

Understanding how the chiral or achiral section in chiral nanostructures contributes to circularly polarized light emission (CPLE) at the atomic level is of fundamental importance. Here, we report two pairs of atomically precise enantiomers of homosilver (R/S-Ag12Ag32) and heterometal (R/S-Au12Ag32) clusters. The geometrical chirality of R/S-Ag12Ag32 arises from the chiral ligand and interface consisting of positive moieties of Ag32(R/S-PS)24. The circular dichroism of R/S-Ag12Ag32 is active, but CPLE-silent. A complete metal change from Ag12 to Au12 in the achiral core section of S2-@M12@S8 engenders isomorphous heterometal R/S-Au12Ag32, which activates CPLE. We further quantify the contributions of achiral and chiral sections and for the first time unveil that heterometal bonding (Au12-Ag32) at the linkage varies the delocalization of orbitals and proportion of achiral and chiral section in electron transition-involved orbitals, thus activating CPLE. Based on these unique atomically precise homochiral metal clusters, our work provides a new insight into the contributions of achiral and chiral sections to the origin of chiroptical response of chiral metal clusters, paving the way to advance the development of CPLE nanoparticles.

Stepwise Achievement of Circularly Polarized Luminescence on Atomically Precise Silver Clusters.

The weakly coordinated anionic nitrate ligands in a centrosymmetric Ag20 cluster are replaced in a stepwise manner by chiral amino acids and two achiral luminescent sulfonic-group-containing ligands while nearly maintaining the original silver(I) cage structure. This surface engineering enables the atomically precise Ag20 clusters to exhibit the high-efficiency synergetic effects of chirality and fluorescence, producing rare circularly polarized luminescence among the metal clusters with a large dissymmetry factor of (|glum|) ≈ 5 × 10-3. This rational approach using joint functional ligands further opens a new avenue to diverse multifunctional metal clusters for promising applications.

Photoresponsive Propeller-like Chiral AIE Copper(I) Clusters.

A pair of propeller-like chiral trinuclear CuI clusters (R/S-Cu3) with unique photoinduced fluorescence enhancement were prepared. R/S-Cu3 showed intense variable luminescence after UV light irradiation, which was attributed to the stepwise oxidation of ligand in the clusters. It exhibited typical aggregation-induced emission (AIE) (αAIE =17.3). Mechanism studies showed that metal cluster-centered (MCC) and triplet metal-to-ligand charge-transfer (3 MLCT) processes are the origin of the luminescence; the processes are regulated by a restriction of intramolecular motions mechanism in a different state. The chiral structure and AIE feature endow R/S-Cu3 with remarkable circularly polarized luminescence (glum =2×10-2 ) in the aggregated state. It shows good capability for producing reactive oxygen species. This work enriches the kinds of atomically precise AIE clusters, gains insight into their luminescence mechanism, and offers the prospect of application in multifunctional materials.

Smart Transformation of a Polyhedral Oligomeric Silsesquioxane Shell Controlled by Thiolate Silver(I) Nanocluster Core in Cluster@Clusters Dendrimers.

Using polyhedral oligomeric silsesquioxane (POSS) modified by a thiol group as a protected ligand, atom-precise multi-heteorocluster-based dendrimers Ag12 @POSS6 (1 a and 1 b) were assembled. Through the reactive -SH groups, six POSS shell ligands stabilize the central 12-core silver(I) cluster by diverse Ag-S interactions. When such Ag12 @POSS6 complex was stimulated by different solvents (acetone or tetrahydrofuran), the core Ag12 silver(I) cluster underwent reversible structural transformation between flattened cubo-octahedral (in 1 a) and normal cubo-octahedral (in 1 b); concomitantly shell POSS clusters rearranged from pseudo-octahedral to quasi-octahedral. Furthermore, the film matrix modified by 1 a or 1 b showed different hydrophobicity.