Tuning of fluorescence by controlling the secondary structure of amino acid-based poly(N-propargylamides) having pendant pyrene groups

Copolymerizations of 1-pyrenebutyric acid N-propargylamide (PY) with chiral amino acid-based N-propargylamides, N-(tert-butoxycarbonyl)-L-valine-N-propargylamide (LV) and N-(tert-butoxycarbonyl)-D-alanine-N-propargylamide (DA) were conducted with (nbd)Rh+[eta(6)-C6H5B-(C6H5)(3)] as a catalyst to obtain novel pyrene-functionalized helical poly(N-propargylamides). The controllable secondary structure of the copolymers by various compositions of the chiral amino acid units or solvent environment led to a controlled orientation of the side-chain pyrene. For instance, poly(PY30-co-LV70) exhibited a large specific rotation and a CD signal, while it emitted very weak fluorescence. On the other hand, poly(PY30-co-LV35-co-DA(35)) exhibited a small specific rotation and a CD signal, while it emitted fluorescence eight times larger than poly(PY30-co-LV70) did. The CD signal disappeared by the addition of MeOH to a THF solution of poly(PY30-co-LV70), while the fluorescence intensity increased.