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Ring carbo-mers of oligo(phenylene ethynylene)s (OPEn, n=0-2), made of C2 -catenated C18 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 C18 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 ??-conjugation. An accurate linear fit of E1/2red1 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 ??-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.

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Interesting 18 π-electron systems involving cyclooctadecanonenetriyne rings have been synthesized and examined by computations.1 The mono-, di- and tri-C18 ring compounds 1, 2, and 3 were prepared and the x-ray structure of 2 was obtained. The B3PW91/6-31G(d,p)...
Chongwei, Z.; Albert, P.; Carine, D.; Brice, K.; Alix, S.; Valrie, M.; Remi, C., Angew. Chem. Int. Ed. 2018, 57, 5640-5644Contributed by Steven BacharachReposted from Computational Organic Chemistry with permissionInteresting 18 -electron systems involving...