Syntheses, Structures, and Properties of Bithiophenophanes Bridged at 1,8-Positions of Naphthalenes

Abstract

The 2,2'-bithiophenophanes 2 and 3 bridged at the 1,8-positions of naphthalenes together with the linear dimers 4 and 6, the trimers 5 and 7, and the tetramer 8 were synthesized by the homo-coupling of l,8-di(5-lithio-2-thienyl)naphthalenes with CuCl 2 . The cyclophane 2, which has no alkyl substituents, shows a hindered rotation of its bithiophene units to give two isomers, of which the major isomer easily isomerized photochemically to produce the minor isomer. In contrast, 3, which has ethyl substituents, shows a rapid rotation of its bithiophene units in solution to afford a mixture of four conformational isomers, although an X-ray analysis of 3 revealed the existence of only one isomer in crystals. The redox and fluorescence behaviors of 2 and 3 show either a face-to-face interaction of the 2,2'-bithiophene units or deformation of the naphthalene moieties. Furthermore, the linear oligomers 4, 5, 6, 7, and 8 show fairly low oxidation potentials and clear emission owing to the π-πt interaction of the face-to-face-stacked thiophene rings.