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 + [ η 6 -C 6 H 5 B - (C 6 H 5 ) 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(PY 30 - co -LV 70 ) exhibited a large specific rotation and a CD signal, while it emitted very weak fluorescence. On the other hand, poly(PY 30 - co -LV 35 - co -DA 35 ) exhibited a small specific rotation and a CD signal, while it emitted fluorescence eight times larger than poly(PY 30 - co -LV 70 ) did. The CD signal disappeared by the addition of MeOH to a THF solution of poly(PY 30 - co -LV 70 ), while the fluorescence intensity increased.