Highly fluorescent aryl-cyclopentadienyl ligands and their tetra-nuclear mixed metallic potassium-dysprosium clusters

Two alkyl substituted triaryl-cyclopentadienyl ligands [4,4 '-(4-phenylcyclopenta-1,3-diene-1,2-diyl)bis(methylbenzene) (1) and 4,4 ',4 ''-(cyclopenta-1,3-diene-1,2,4-triyl)tris(methylbenzene) (2)] have been synthesized via cross-aldol condensation followed by Zn-dust mediated cyclization and acid catalyzed dehydration reactions. The fluorescence properties of 1 and 2 have been studied in solution and solid state. The ligands exhibited aggregation-induced emission enhancement (AIEE) in THF/water solution. 1 and 2 have been found to be significantly more fluorescent in the solid state than in their respective solutions. This phenomenon can be attributed to the strong intermolecular CHMIDLINE HORIZONTAL ELLIPSIS pi interactions present in 1 and 2 which leads to the tight packing of molecules in their solid-state. Both 1, 2 and their corresponding anions have been studied by theoretical calculations. Ligands 1 and 2 have been shown to react with anhydrous DyCl3 in the presence of potassium metal at high temperature to afford two fluorescent chloride-bridged tetra-nuclear mixed potassium-dysprosium metallocenes [(Me2Cp)(4)(Dy2Cl4K2)-Cl-III]center dot 3.5(C7H8) (5) and [(Me3Cp)(4)(Dy2Cl4K2)-Cl-III]center dot 3(C7H8) (6), respectively in good yields.