Synthesis and Structure of Optically Active Oligo(N‐substituted‐m‐benzamide)s Bearing a Bithiophene Chromophore on the Benzene Ring

Abstract

An optically active oligo(m‐benzamide) (OBA1), with a chiral alkyl group on the amide nitrogen and a bithiophene chromophore on the benzene ring by the chain‐growth polymerization of methyl 3‐((S)‐2′‐methylbutylamino)‐5‐(2′′‐(5′′,2′′′‐bithienyl)) benzoate are prepared. In addition, unimer to trimer model compounds (M1, M2, and M3) are synthesized by the iterative ester hydrolysis and dehydration condensation. An optically active oligo(m‐benzamide) with a chiral methoxyethoxyethoxy group (OBA2) is likewise synthesized. On the basis of electronic circular dichroism (CD), UV–vis, and fluorescence spectra, the chiral arrangement of bithiophene chromophores is discussed. By converting the carbonyl group in OBA1 into the methylene group using LiAlH4/AlCl3, a bisignate Cotton effect is collapsed, indicating the importance of the aromatic tertiary amide skeleton for the chiral arrangement of chromophores. The chain conformation of OBA1 is further investigated by means of theoretical CD calculations to figure out that two neighboring bithiophene units are preferentially rotated in a counterclockwise direction.