Carbo ‐biphenyls and Carbo ‐terphenyls: Oligo(phenylene ethynylene) Ring Carbo ‐mers

Abstract Ring carbo ‐mers of oligo(phenylene ethynylene)s (OPE n , n =0–2), made of C 2 ‐catenated C 18 carbo ‐benzene rings, have been synthesized and characterized by NMR and UV‐vis spectroscopy, crystallography and voltammetry. Analyses of crystal and DFT‐optimized structures show that the C 18 rings preserve their individual aromatic character according to structural and magnetic criteria (NICS indices). Carbo ‐terphenyls ( n =2) are reversibly reduced at ca. −0.42 V/SCE, i.e. 0.41 V more readily than the corresponding carbo ‐benzene (−0.83 V/SCE), thus revealing efficient inter‐ring π‐conjugation. An accurate linear fit of E 1/2 red1 vs. the DFT LUMO energy suggests a notably higher value (−0.30 V/SCE) for a carbo ‐quaterphenyl congener ( n =3). Increase with n of the effective π‐conjugation is also evidenced by a red shift of two of the three main visible light absorption bands, all being assigned to TDDFT‐calculated excited states, one of them restricting to a HOMO→LUMO main one‐electron transition.