Assembly‐Induced Strong Circularly Polarized Luminescence of Spirocyclic Chiral Silver(I) Clusters

Abstract

Spirocyclic Ag 9 clusters, as a new form of intrinsically chiral metal clusters, were constructed through vertexsharing of two in-situ-generated heteroaryl diide-centered metal rings. Such core-peripheral type clusters exhibit versatile photoluminescent and chiroptical behavior under different aggregation conditions. In contrast to a ligand-based fluorescence emission in a diluted solution of the clusters, a solvent polarity-caused assembly gives rise to new cluster-based phosphorous luminescence owing to radiative mode switching and aggregation-induced emission. Assembly of cluster enantiomers leads to micrometer-long helical nanofibers, whose handedness is determined by absolute configuration of individual spirocyclic clusters. Benefiting from exciton couplings of helical arrangements of chelating ligands at molecular and microscopic levels, the assembled film of cluster enantiomers exhibits circularly polarized luminescence with a high anisotropy factor (0.16).Scheme 1. Synthesis of spirocyclic clusters 1 and 2-(S).

Multiresponsive Luminescent Behaviors of Assembled Spirocyclic Nonanuclear Silver(I) Clusters

“…UV-vis spectra of 2-4 in a diluted methanol solution exhibited an intense high-energy absorption peak at 285-330 nm, similar to 1, and originated mainly from intra-PBZ π→π* transition. 65 As a result, their emission spectra showed the same emission band maximum at around 366 nm regardless of different indolyl-2,3-diide centers in 1-4 (Figure 3a). Upon increasing the concentration from 4.0 × 10 −6 to 3.0 × 10 −4 M, a new low-energy absorption peak at 408-412 nm appeared gradually in the spectra of 1-4 (Figure 3b and Supporting Information Figure S7), assigned as indole-2,3-diide-to-PBZ ligandto-ligand charge transfer, together with some Ag-to-PBZ metal-to-ligand charge transfer.…”

“…Synthesis and crystal structure of complex 1 has been reported previously. 65 All other reagents, unless specified, were of analytical grade and were used as received without further purification.…”

“…[Ag 9 (PBZ) 8 (butyl-indole-2,3-diide) 2 ] (CF 3 SO 3 ) 5 •(CH 3 OH) (2) The synthetic procedures for 2 are similar to that of 1. 65 Briefly, in a 5 mL round-bottom flask, AgCF 3 SO 3 (64.2 mg, 0.25 mmol) and PBZ (39.0 mg, 0.2 mmol) were added and dissolved in a mixed solvent of CH 3 OH/ CH 2 Cl 2 (v∶v = 1∶1, 1.0 mL) at room temperature. After vigorous stirring for 10 min, 4-butyl-2-ethynylaniline (8.7 mg, 0.05 mmol) dissolved in the mixed solvent of CH 3 OH/CH 2 Cl 2 (v∶v = 1∶1, 0.5 mL) was added dropwise.…”

“…The spirocyclic Ag 9 clusters 2-4 were synthesized using different alkyl-substituted derivatives of 2-ethynylaniline (Scheme 1), according to the previously reported synthetic protocol for complex 1. 65 The structures of 1-4 were determined by X-ray crystallographic analysis; selected bond lengths are listed in Figure 1 and Supporting Information Table S1. The spirocyclic Ag 9 skeletons in Scheme 1 | Synthesis of spirocyclic nonanuclear silver clusters 1-4.…”

“…We recently reported the synthesis of spirocyclic silver clusters through the vertex-sharing of heteroaryl diide-centered metal rings. 65 The overall spirocyclic skeleton in the complex Ag 9 (PBZ) 8 {indole-2,3-diide} 2 ](CF 3 SO 3 ) 5 (1) was stabilized by a couple of π-π stacking arrays of planar chelating ligands no matter what kind of heteroaryl diides. We noted the high structural similarity of the cluster core but distinct intra-and intercluster π-π stacking patterns of peripheral ligands, which provided an ideal molecular platform to study the detailed self-assembly process of metal clusters and their related photophysical properties.…”