Metal Chalcogenide Supertetrahedral Nanocluster:Assembly,Discretization And Their Optical Properties

Metal-chalcogenide supertetrahedral Tn nanoclusters are structurally consistent with the tetrahedral fragments of Cubic-ZnS,and bear the closest resemblance to traditional II-VI or ?-?-? semiconductor quantum dots(QDs),thus generally described as ultra-small semiconductor 'QDs'.However,being different from traditional colloidal semiconductor QDs.metal-chalcogenide supertetrahedral clusters(MCSCs)have absolutely-uniform size,precise surface and internal structure,and atomically-precise doping sites.The study on the relationship between the composition-structure-property of MCSCs can theoretically help to understand some photophysical behaviors of traditional QDs that are difficult or impossible to clarify.It should be clarified that the construction and enrichment of MCSCs,and the determination of their existing form in lattice are the premise to conduct the above research.Previous research has shown that the MCSCs in the mother liquor can be assembled into a framework via corner sharing modes(S/Se),or crystallize in the superlattice with discrete forms in a few cases.However,it is difficult to achieve a breakthrough in structural novelty with the traditional connection modes after nearly 30 years of development;moreover,in large-sized cluster-based crystalline materials,the discrete clusters in crystal lattice are often limited by strong electrostatic interactions,which makes it difficult to achieve a high dispersibility in solvents,and therefore cannot be regarded as a true nanomaterial.This paper aims to expand the inter-cluster connection modes of MCSCs,and to handle the issues of clusters' discretization in lattice and dispersion in solvent.The detailed research is included in the following two aspects:1.To expand the hybrid assembly of Tn-type nanoclusters and organic ligands,and the hybrid assembly of Tn-type nanoclusters of different sizes.Firstly.we obtained two compounds of cluster-based hybrid framework materials(SCIF-11 and SCIF-12)with imidazole(IM)ligands and Tn nanoclusters.In which.SCIF-11 has hybrid inter-cluster bridging modes(Tn-IM-Tn.Tn-S-Tn).while SCIF-12 has a 3,4-connected interrupted framework with the first ins topology in Tn cluster-based frameworks.The experimental results show that the introduction of organic imidazole ligand has a significant effect on their band gaps and photoluminescence.Secondly,we for the first time realized the assembly of carboxylic acid ligands and Tn clusters by balancing the coordination ability between O/S and In3+ions.and obtained a two-dimensional hybrid framework IOS-1 with good conductivity.It is worth noting that the cluster unit in IOS-1 represents the largest supertetrahedral oxysulfide nanoclusters among Tn series,which was further assembled with imidazole and obtained IOS-2(P&M)with qtz chiral structure.Finally,we also realized the hybrid assembly and co-assembly of different size/component Tn clusters(T3-InS and T5-InOS).Absorption spectra show that the differences in clusters'sizes and coupling have significant effects on the absorption properties of the final framework materials.2.Designed synthesis and photocarrier dynamics of discrete metal-chalcogenide semiconductor nanoclusters.The isomorphic and largest discrete penta-supertetrahedral P2 nanoclusters(P2-CuInSnS(P2-In),P2-CuGaInSnS(P2-GaIn)and P2-CuGaSnS(P2-Ga))were designed synthesized under the guidance of multivalent mixed-metal complementary strategy and superbase assisted crystallization strategy.The intentional introduction of high content of Sn4+ions were found to make P2 nanoclusters exhibit excellent aqueous dispersibility(H2O:acetone?1:1)and long-term stability that in the form of cluster-based ultra-small nanoparticles(also known as supraclusters).Based on the dispersions of P2 nanoclusters,we studied their steady-state absorption spectra and found a systematic red shift with the introduction of Ga3+ions.The first principle calculations indicated that the substitution of In with Ga indirectly affects the band structure by disturbing the electronic structure of the surrounding atoms.and the conduction band regions gradually approach the Fermi level.which results the red shift of the spectra.In addition.femtosecond transient absorption spectroscopy was employed to study their excited-state dynamics.The systematical change in the amplitudes of decay components was correlated with the composition variation.which reasonably expounds the intracluster"core-shell" relaxation pathway when integrating the molecular orbitals and regarding the P2 nanocluster as a "core-shell" hierarchical structure.The results of this paper will provide experimental and theoretical guidance,and novel research ideas for the synthesis of metal-chalcogenide cluster-based hybrid framework materials,the solvent dispersion of large-sized discrete MCSCs,and the photodynamic of semiconductor nanoclusters.