[4]Cyclofluorene: unexpected influence of alkyl chain length

Abstract : Molecular nanorings have attracted a lot of interest the last ten years. Here we present the study of a new example of [4]cyclofluorene, with ethyl chains on the bridgeheads. Its molecular structure was established by solution NMR spectroscopy and single-crystal X-ray diffraction. Three successive oxidation processes and one reversible reduction were observed via cyclic voltammetry. The optical properties were characterized both in solution and film by UV-visible spectroscopy, stationary and time-resolved fluorescence. It was found that this [4]cyclofluorene displays different characteristics compared to the other [4]cyclofluorenes substituted by methyl or propyl chains: a simple modification of the chain length induces a non-negligible effect on the emission properties which must be linked to the specific arrangement of the fluorene units. Furthermore, single-crystal X-ray diffraction reveals the formation of a pseudo-tubular solid state arrangement of fully symmetrical ring structures, which was not observed for the other members of the [4]cyclofluorenes family. This feature, never discussed to date, could open the way to the modulation of properties of cyclofluorenes through alkyl chain engineering.
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Lambert Sicard, Olivier Jeannin, Joëlle Rault-Berthelot, Cassandre Quinton, Cyril Poriel. [4]Cyclofluorene: unexpected influence of alkyl chain length. ChemPlusChem, Wiley, 2018, 83 (9), pp.874-880. ⟨10.1002/cplu.201800369⟩. ⟨hal-01890153⟩



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