Abstract
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.
Highlights
Monomer-3, containing point and axial chirality derived from glucose and biaryl units, respectively, was synthesized from a previously reported 5,50dibromobithiophene derivative,1,41 through acetal deprotection followed by esteri cation at the 4- and 6-positions of the glucose unit
Intense CD signals derived from the helical chirality of poly-TR were observed in various solvent systems, including tetrahydrofuran and chlorobenzene, which are typically good solvents for polythiophenes (Fig. S5†). This is the rst example of a molecularly dispersed one-handed helical polythiophene existing under good solvent conditions, Chart 1 the p-conjugated backbone of poly-TR was considered to fold into a helical conformation
Based on the comprehensive chiroptical study using poly-TR, its analogous polymer and model compounds, we concluded that the poly-TR backbone possessed a speci c secondary structure even under good solvent conditions, such as in chloroform, THF and chlorobenzene
Summary
A simple poly(thiophene-2,5-diyl) without any pendant groups was successfully synthesized via chemical polymerization in 1980.1,2 In the last four decades, much research effort has been focused on developing a range of functional polythiophenes ( referring to poly(thiophene-2,5-diyl)s, unless otherwise noted) using various polymerization techniques and/or postpolymerization modi cations.[3,4,5,6,7,8,9] Polythiophenes are recognized as an important class of p-conjugated polymers and have been extensively studied for applications in organic devices and functional materials, including as photovoltaics, eld-effect transistors, light emitting diodes, magneto-optics, actuators and chemical/biological sensors.[10,11,12,13,14,15] This practical utility arises from their excellent semiconducting, optical and magnetic features, in addition to substantial environmental stability and mechanical strength.Chiral polythiophenes containing optically active components somewhere in the molecular structures have attracted considerable attention in the elds of supramolecular4890 | Chem. 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.
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