Dissymmetric Chiral Poly(diphenylacetylene)s: Secondary Structure Elucidation and Dynamic Luminescence

Abstract

The secondary structure of a dissymmetric and chiral poly(diphenylacetylene) (PDPA) is elucidated by combining the data from NMR experiments (regioregular head to tail structure), Raman and IR studies (E configuration of the polyene double bonds), and high‐resolution AFM images (helical pitch, packing angle and orientation of the external helix). As a result, an E‐transoidal polyene backbone describing three coaxial helices is obtained. Theoretical electronic circular dichroism (ECD) studies of the structure show a good correspondence between experimental and theoretical data and allow one to decipher that the first Cotton band is generated by the poly(diphenylacetylene) core and not only by the polyene backbone. The dynamic behavior of poly‐(S)‐2 is also demonstrated by a helix inversion effect produced by conformational changes at the pendant groups when annealed in solvents with different donor abilities. This phenomenon is accompanied by an inversion of the circular polarized luminescence of the PDPA (CPL switch).

Diastereomeric multi‐chiral pendant groups: Their key role in stimuli‐responsive polymeric responses

“…In consequence, a large variety of non‐natural foldamers and helical polymers have been studied during the last decades. In the special case of helical polymers, families such as poly(isocyanide)s, 3 poly(isocyanate)s, 4 poly(diphenylacetylene)s, 5,6 or polyacetylenes, 7,8 among others, provide a large variety of helical scaffolds with different static/dynamic, which properties find applications in different fields such as chiral materials asymmetric catalysis, 9–13 chiral recognition, 14,15 circular polarized luminescence (CPL) sources, 5,6,15,16 chiroptical switches, 17,18 or chiral stationary phases for high performance liquid chromatography (HPLC) among others 19–21 . To be functional, these helical polymers must adopt macromolecular helical structures with screw sense excess.…”