Aluminum is an important component for luminescence. However, the fluorescent aluminum complex with unambiguous structural information is still limited. Herein, we report a series of fluorescence aluminum oxo clusters (AlOCs). By introducing an additional coordination site to the aromatic conjugation ligand, cluster nuclearity increment and fluorescence variation are observed. Al8(OH)2(μ4-O)2(1-NA)2(OEt)16 (AlOC-41, 1-NA = 1-naphthoic acid, OEt = ethanol) is made up of two tetrahedral subunits. By introducing an additional coordination site to the aromatic conjugation ligand, we isolate a high nuclearity compound Al10(μ3-O)2(3-HNA)2(OEt)22 (AlOC-47, 3-HNA = 3-hydroxy-2-naphthoic acid). Correspondingly, their luminescence performance is different (blue fluorescence in AlOC-41 and green in AlOC-47). Present herein is a platform to illustrate the relationship between synthesis, structure, and fluorescence properties.
Graphical The solvothermal synthesis of low nuclearity aluminum clusters to polynuclear aluminum clusters was achieved by regulating the amount of nitrogen-containing ligands. Present herein is the currently largest catecholato-based aluminum oxo clusters. By adjusting the amount of auxiliary 3, 5-dimethylpyrazole ligands, the synthesis of aluminum oxo clusters (AlOCs) ( AlOC-86 ) to high nuclearity AlOCs ( AlOC-88 ) were successfully achieved. Such synthetic strategy is applicable to imidazole ligands and new compounds ( AlOC-87 and AlOC-89 ) were obtained. Single crystal analysis shows that AlOC-86 and AlOC-87 are hexanuclear clusters made up of two edge-sharing tetrahedral clusters. The nuclearity of compounds AlOC-88 and AlOC-89 is doubled and they are S-shape dodecanuclear AlOCs. The aggregation of such clusters is attributed to the labile sites on the two ends of the hexanuclear clusters. In addition, open aperture (OA) Z-scan measurements results indicate that these compounds exhibit manifest reverse saturation absorption (RSA) response.
Comprehensive Summary This study highlights the innovative use of increased rare earth elements to enhance the dielectric properties of materials and devices. The AlOC-129Ln series, features the highest number of rare earth dopants in aluminum oxo clusters to date. The trivalent ions in AlOC-129Ln impart a high dipole moment, significantly elevating the dielectric constant ( k ) of the doped polymer films. AlOC-129Ce, in particular, exhibits the largest molecular size, which enhances interfacial effects and achieves a relative dielectric constant four times greater than that of undoped polymers and 1.5 times higher than those with single rare earth dopants. The substantial molecular size (~2.5 nm) and robust charge scattering and trapping capabilities of AlOC-129Ln reduce dielectric loss by up to 50% at high frequencies. Additionally, its excellent solution processability enhances breakdown strength by 147%, ensuring superior electrical stability. This research demonstrates the versatility of the cluster doping strategy in effectively balancing dielectric constant and loss, unveiling the promising potential of solution-processable cluster materials in electronic devices.
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