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revised on 29.04.2020 and posted on 30.04.2020by Kaige Zhu,, Kosuke Kamochi, Takuya Kodama, Mamoru Tobisu, Toru Amaya
Chiral cyclic [n]spirobifluorenylenes consisting of helically arranged quaterphenyl rods, illustrating partial units of woven patterns, were designed and synthesized as a new family of carbon nanorings. The synthesis was accomplished by the Ni(0)-mediated Yamamoto-coupling of chiral spirobifluorene building blocks. The structures of the cyclic 3-, 4-, and 5-mers were determined by X-ray crystallographic analysis. These carbon nanorings exhibited a strong violet colored emission with high quantum yields in solution (95%, 93%, and 94% for 3-, 4-, and 5-mer, respectively). Other spectroscopic properties, including their chiroptical properties, were also investigated. The g-values for circularly polarized luminescence were found to be in the order of 10-3, where that of the 4-mer showed a relatively higher value 8.5 x 10-3. Characteristic spiroconjugation induced by multiple 3) bifluorenyl units, for example the even-odd effect of the number of units in the matching of the sign of the orbitals, were also indicated by DFT calculations.