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Controlling the Flipping Motion of Cycloparaphenylene Dimers
Zhuofan Xu1, Xingchi Liu1, Chang Ge1
1Institute of Molecular Plus, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, 92 Weijin Road, Tianjin 300072, P. R. China.
None:
Inhibiting both the rotating and flipping processes is a prerequisite for constructing cycloparaphenylene (CPP) dimers with well-defined conformation and chirality. Configurationally stable CPP dimers 1 and 2 are synthesized using cyclocondensation as a key step, from a newly designed diketone macrocyclic precursor. Variable-temperature nuclear magnetic resonance analyses and theoretical calculations confirmed that the flipping process of both CPP rings of 2 was inhibited, while only one CPP ring was allowed for flipping for 1. This control over flipping dynamics is achieved by the introduction of sterically demanding substituents. Steady-state fluorescence spectroscopy and theoretical calculations revealed solvatochromic behavior in the emission for 1 and solvent-dependent anti-Kasha emission for 2. A 1:2 host-guest complex of dimer 2 and C70 was established, showing negative cooperativity.
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