Synthesis and optical properties of 1,1-binaphthyl-thiophene alternating copolymers with main chain chirality

A series of axially chiral 1,1-binaphthyl-thiophene copolymers were synthesized by Migita-Kosugi-Stille polycondensation and electrochemical polymerization. The polymers exhibit circular dichroism not only in the ultraviolet region but also in the visible region, both in solution and film states. Optical and electrochemical properties of the polymers are in good agreement with theoretical results obtained by density functional theory calculations. Although effective conjugation of the polymers was cleaved at the orthogonally oriented two naphthalene rings in the 1,1-binaphthyl unit, the electrochemically synthesized polymer film shows good electrochemical redox behavior with repeatable changes in optical absorption and circular dichroism. The changes in circular dichroism may reflect a change in the dihedral angle of the binaphthyl unit caused by reorientation of conjugated main chains between oxidized and neutral states.