Chiral-to-Chiral Communication in Polymers: A Unique Approach to Control both Helical Sense and Chirality at the Periphery

Abstract

A novel approach to the classical Sergeants and Soldiers effect, using chiral Sergeants and chiral Soldiers, allows control over both helical and external chirality in helical polymers. In the systems reported here, it is possible to induce the same helical sense (M or P) from either of the two enantiomers of a chiral pendant group [“chiral Soldier”, major component; i.e., (R)- or (S)-1] when it faces a single enantiomer of an appropriate “chiral Sergeant” [minor component; i.e., (S)-2]. For instance, the copolymer series poly[(R)-1r-co-(S)-2(1–r)], poly[(S)-1r-co-(S)-2(1–r)], and poly[(rac)-1r-co-(S)-2(1–r)] adopt the same P helix even though the major component shows the opposite absolute configuration. This chiral-to-chiral communication effect is transmitted by the stabilization of different conformations in each enantiomeric form of the Soldier. As a result, this groundbreaking approximation to the Sergeants and Soldiers effect allows the preparation of a single-handed helix—which depends only on the Sergeant’s configuration—with different chiralities on the helix periphery. Thus, a P helix can be decorated with the R isomer, S isomer, or even a racemic mixture of the chiral Soldier. A change in the absolute configuration of the Sergeant affords the opposite M helix, which can also be decorated with the R isomer, S isomer, or racemic mixture of the chiral Soldier