[n]‐Cyclo‐9,9‐dibutyl‐2,7‐fluorene (n=4, 5): Nanoring Size Influence in Carbon‐Bridged Cyclo‐para‐phenylenes

Abstract

For the last ten years, ring‐shaped π‐conjugated macrocycles possessing radially directed π‐orbitals have been subject to intense research. The electronic properties of these rings are deeply dependent on their size. However, most studies involve the flagship family of nanorings: the cyclo‐para‐phenylenes. We report herein the synthesis and study of the first examples of cyclofluorenes possessing five constituting fluorene units. The structural, optical and electrochemical properties were elucidated by X‐ray crystallography, UV‐vis absorption and fluorescence spectroscopy, and cyclic voltammetry. By comparison with a shorter analogue, we show how the electronic properties of [5]‐cyclofluorenes are drastically different from those of [4]‐cyclofluorenes, highlighting the key role played by the ring size in the cyclofluorene family.

[4]Cyclo-N-alkyl-2,7-carbazoles: Influence of the Alkyl Chain Length on the Structural, Electronic, and Charge Transport Properties

“…This not only shows the versatility of these experimental conditions but also highlights that the alkyl chain length does not have any impact on the reaction yield. A different result has been recently reported for structurally related fluorene nanorings, for which the alkyl chain borne by the bridge has a significant impact on the reaction yield 14.…”

“…In nanoring chemistry, the mean torsion angle θ between adjacent carbazole rings is an important parameter driving the electronic properties. this behavior (the largest θ observed for the shortest chain) may be surprising, but the same was observed for 4cyclofluorenes, 14,23,32 and assigned to steric hindrance of alkyl chains that forces the alignment of the constituting units. ).…”

“…A different result has been recently reported for structurally related fluorene nanorings, for which the alkyl chain borne by the bridge has a significant impact on the reaction yield. 14 The transmetallation step has also been studied as a function of the reaction solvent. In the above mentioned experimental conditions, THF was used, as commonly found in literature.…”

“…This conformation is consistent with that obtained with other bridged-CPPs. 14,23,36 and Cm space groups respectively (see X-ray diffraction tables in SI). [4]C-Et-Cbz crystallizes with a molecule of chloroform outside of the nanoring cavity, with which there is no apparent interaction.…”

“…These studies have mainly focused on the influence of the nanoring size and of the building units on the structural, electronic and chiral properties. [3][4][5][6][7][8][9][10][11][12][13][14] As recently reviewed by Jasti and coworkers, 15 nanorings can cover a broad range of applications including imaging tools in biology, 16 complexing agent for single-walled carbon nanotubes 17 or fullerenes, [18][19][20] carbon-based porous material, [21][22] solid state emitters, 11,[23][24] or spin crossover compounds. 25 Molecular nanorings are now considered for their potential applications in organic electronics.…”