Synthesis and Property of Three-dimensional Curved Heterocyclic π-Electron Molecules with Embedded Nitrogen Atoms

The synthesis and property of new three-dimensional curved heterocyclic pi-electron molecules with embedded nitrogen atoms such as helix-, butterfly-, bowl-, and flake-shaped molecules were investigated. Particularly, novel heterocyclic molecules with an embedded hydrazine structure were focused. Hydrazine-embedded helix-shaped bicarbazole, bidimethylacridine, and biphenothiazine were synthesized by dimerization of the corresponding heterocycles. The hydrazine-embedded helical molecules were found to undergo electron transfer disproportionation by acid stimulus, forming their stable radical cations and reduced species through the acid triggered N-N bond cleavage reaction. In the case of bidimethylacridine, the disproportionation reaction is highly reversible through neutralization with NEt3 through back electron transfer and N-N bond formation. Utilizing their reversible redox property, the hydrazine-embedded molecules were applied to cathode active materials of rechargeable lithium organic batteries with excellent performance. Ni-mediated coupling of dibromo-dimethylacridine, phenothiazine, or acridone was found to afford double-butterfly-shaped cyclodimers in high yields. Following N-N bond formation gave hydrazine-embedded butterfly-shaped or planar molecules. The double butterfly-shaped cyclobiphenothiazine was converted to a cyclodimer of carbazole, [2]cyclo-1,8-carbazolylene, through reductive desulfurization. N-N bond formation of [2] cyclo-1,8-carbazolylene afforded hydrazine-embedded bowl-shaped bicarbazole. The bicarbazole was found to possess bowl and twist structures in the neutral state, a shallow bowl structure in the monocation state, and a planar structure in the dication state by X-ray analysis, C-13 NMR, and DFT calculations. Hydrazine-embedded helix-, butterfly-, and bowl-shaped molecules expressed reversible oxidation at a wide range of potentials and red-shift of absorption and fluorescence. The bowl shaped dimer, a flake-shaped cyclotrimer, a square-shaped cyclotetramer, and a hexagon-shaped cyclohexamer of carbazole were synthesized by Ni-mediated coupling of 1,8-dibromocarbazole, and were named [n] cyclo-1,8-carbazolylenes (n = 3,4,6). A flake-shaped [3] cyclo-4,6-dibenzofuranylene was also obtained from dibromodibenzofuran. B, P, and Si atoms were introduced to [3]cyclo-1,8-carbazolylene, giving flake-shaped complexes.