Dissymmetric Chiral Poly(diphenylacetylene)s: Secondary Structure Eluci

Abstract

The 3D helix adopted by a non-symmetric substituted poly(diphenylacetylene) (PDPA) is elucidated, and its ability to self-assemble into nanospheres or fiber-like structures under the right conditions is also demonstrated. Moreover, by conformational changes in the pendant group it is possible to produce a helix inversion in the PDPA and create a circular polarized luminescence (CPL) switch. 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)