Carbo -cyclohexadienes vs. carbo -benzenes: structure and conjugative properties

• Published in: Chemical science (Cambridge) 2015-01, Vol.6 (2), p.1139-1149
• Main Authors: Rives, Arnaud, Baglai, Iaroslav, Barthes, Cécile, Maraval, Valérie, Saffon-Merceron, Nathalie, Saquet, Alix, Voitenko, Zoia, Volovenko, Yulian, Chauvin, Remi
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Chromophores; Coordination chemistry; Crystal structure; Diffraction; Reduction; Spectra; Spectroscopic analysis; Spectroscopy; X-rays
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c4sc02742f

Ideally -/ -symmetric chromophores, constituted by two electro-active groups conjugated through the -mer of the cyclohexa-1,3-diene core, are selectively prepared by the SnCl -mediated reduction of tailored hexaoxy-[6]pericyclynes: in the latter substrates, one of the 1,4-dioxybut-2-yne edges is "chemically locked" by two CF substituents preventing complete reduction to the corresponding aromatic -benzenic core, which is expected to be more "π-insulating" between the electro-active ends. The bis-trifluoromethylated -cyclohexadiene products are also shown to be significantly stabilized with respect to their bis-phenylated analogues. Their structural (crystal X-ray diffraction analyses), spectroscopical (NMR and UV-vis spectra), physio-optical (dichromism in solution) and electrochemical (cyclic voltammograms) properties are compared on the basis of the electron-donating/electron-withdrawing nature of the substituents. These properties are also compared with those of their aromatic -benzene and flexible -butadiene counterparts.