Synthesis and chiroptical properties of a π-conjugated polymer containing glucose-linked biphenyl units in the main chain capable of folding into a helical conformation

Abstract

An optically active π-conjugated polymer (poly-9) containing glucose-linked biphenyl units in the main chain was synthesized through the copolymerization of 5,5′-diiodo-2,2′-bithiophene and a new diethynyl compound, whose molecular design has taken inspiration from naturally occurring ellagitannins. The chiroptical properties of poly-9 were investigated in solution and the solid state. The absorption and circular dichroism spectra of poly-9 were clearly changed depending on the solvents due to the conformational alteration within a single polymer chain. Because a corresponding model molecule and polymer did not show marked solvent-dependent spectral changes, the backbone conformation of poly-9 is considered to be capable of interconverting between random-coil and preferred-handed helical states in response to the exterior environment. We also found that poly-9 exhibited efficient circularly polarized luminescence with a green color, whose dissymmetry factor reached 1.9 × 10⁻² when the backbone was folded into the helical conformation in the film state.