Zhao-Zhen Cao

Near-Infrared Emitters: Stepwise Assembly of Two Heteropolynuclear Clusters with Tunable AgI:ZnII Ratio

Two 3d-4d heteropolynuclear clusters with Ag-Zn ratios of 9:2 and 9:4 were stepwise constructed from a robust nonanuclear silver cluster. Their crystal structures consist of a common bucket-shaped [Ag9(mba)9](9-) (H2mba = 2-mercaptobenzoic acid) core with different numbers of Zn(II) connected by different exo-oriented carboxylates. Most fascinating is the observation of emission (∼703 nm) in the near-infrared (NIR) region at 300 K that may be compared to the related Ag9Zn3 cluster with aliphatic polyamine as auxiliary ligand that emits from the visible (∼580 nm). The shift is associated with the change of ligand field of the 2,2-bipyridine. The emission intensity and lifetime were dramatically enhanced along with the slight bathochromic shift upon cooling from 300 K to 80 K. The results raise two significant issues: (a) the structural and electronic effects of the secondary metal binding to the metalloligand and the factors influencing the heteropolynuclear cluster assembly and (b) the use of NIR fluorescence, introduced by integrating two luminophores into one heteropolynuclear entity, in detecting free-moving zinc in biological systems both in vivo and in vitro.

High‐Nuclear Organometallic Copper(I)–Alkynide Clusters: Thermochromic Near‐Infrared Luminescence and Solution Stability

Cu(CF3 COO)2 reacts with tert-butylacetylene (tBuC≡CH) in methanol in the presence of metallic copper powder to give two air-stable clusters, [CuI15 (tBuC≡C)10 (CF3 COO)5 ]⋅tBuC≡CH (1) and [CuI16 (tBuC≡C)12 (CF3 COO)4 (CH3 OH)2 ] (2). The assembly process involves in situ comproportionation reaction between Cu2+ and Cu0 and the formation of two different clusters is controlled by reactants concentration. The clusters consist of Cu15 and Cu16 cores co-stabilized by strong by σ- and π-bonded tert-butylethynide and CF3 COO- (together with methanol molecule in 2). Their stabilities in solution were confirmed using electrospray ionization mass spectrometry in which the cluster core remains intact for 1 in chloroform and acetone, and for 2 in acetonitrile. Strong thermochromic luminescence in the near infrared (NIR) region was observed in the solid-state. Of particular interest, the emission maximum of 1 is red-shifted from 710u2005nm at 298u2005K to 793u2005nm at 93u2005K, along with a 17-fold fluorescence enhancement. In contrast, 2 exhibits red shift from 298 to 123u2005K followed by blue shift from 123 to 93u2005K. The emission wavelength was correlated with the structural parameters using variable-temperature X-ray single-crystal analyses. The rich cuprophilic interaction plays a significant role in the formation of 3 LMCT (tBuC≡C→Cux ) excited state mixed with cluster-centered (3 CC) characters, which can be considerably influenced by temperature, leading to thermochromic luminescence. The present work provides 1)u2005a new synthetic protocol for the high-nuclear CuI -alkynyl clusters; 2)u2005a comprehensive insight into the mechanism of thermochromic luminescence; 3)u2005unusual emissive materials with the characters of NIR and thermochromic luminescence simultaneously.