Synthesis of a one-handed helical polythiophene: a new approach using an axially chiral bithiophene with a fixed syn-conformation†
We report an optically active polythiophene capable of forming a one-handed helically folded conformation without needing aggregate formation, poor solvent conditions, hydrogen-bonded ion-pair formation or guest addition. The target polythiophene (poly-TR) with a static axial chirality in the main chain was synthesized via Stille coupling copolymerization of a glucose-linked chiral 5,5′-dibromobithiophene with 2,5-bis(stannyl)thiophene. Poly-TR showed a characteristic circular dichroism and circularly polarized luminescence, which were completely different to those observed for an analogous polymer (poly-PhR) and the corresponding unimer/dimer model compounds. This chiroptical study, combined with the results of all-atom molecular dynamics simulations, revealed that poly-TR can fold into a left-handed helical conformation under good solvent conditions. Partial conformational regulation derived from the fixed syn-conformation of the chiral bithiophene unit was considered a key factor in producing the one-handed helical polythiophene.