-cyclohexadienes -benzenes: structure and conjugative properties.

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.