Donor–Acceptor Nanohoops: Impact of the Ratio and Arrangement of the Fluorenone and Carbazole Moieties

We report herein the synthesis and characterization of four donor-acceptor nanohoops incorporating fluorenone and carbazole as electron-poor and electron-rich units, respectively. The well-known platinum-mediated cyclization reaction here provides, in high yields, a mixture of four nanohoops possessing different and unexpected molecular arrangements. The four nanohoops have been isolated and characterized, and the impact of the number and arrangement of the carbazole and fluorenone moieties has been studied by spectroscopic and electrochemical analyses. Thanks to the intramolecular charge transfer resulting from the interaction between the carbazole and fluorenone units, their fluorescence was significantly red-shifted by 100 nm compared with a cyclic 2,7-tetracarbazole. This work highlights the singularity of the platinum-mediated cyclization reaction to construct donor-acceptor nanohoops with molecular arrangements, which are challenging to reach by other synthetic methods.