Synthesis of Molecular Nanohoops Bearing a Tetrahydro[6]cycloparaphenylene Fused to a Hydrogenated or a Bithiophene-Inserted Cycloparaphenylene.

A synthetic pathway to a molecule bearing two molecular nanohoops, including a tetrahydro[6]cycloparaphenylene (4H[6]CPP) fused through two 1,4-dimethoxybenzene units to a 4H[10]CPP, was developed. Similarly, a molecule containing a 4H[6]CPP fused through two 1,4-dimethoxybenzene units to a molecular nanohoop bearing a [6]CPP inserted with two 2,2'-bithiophene-5,5'-diyl groups was synthesized. The Diels-Alder reactions of two (E,E)-1,4-diaryl-1,3-butadienes with 1,4-benzoquinone and the Ni-mediated homocoupling reactions are the key steps for the construction of macrocyclic ring structures. Oxidative aromatization with DDQ converted a hydrogenated system to a fully aromatized nanohoop with 10 aromatic units, including a [6]CPP inserted with two 2,2'-bithiophene-5,5'-diyl groups. The UV-vis and fluorescence spectra of the fused two-hoop systems were investigated.