Synthesis and chiroptical properties of (Optically active poly(ethynylcarbazole) derivatives: Substituent effect on the helix formation

Novel chiral acetylene monomers containing carbazole, 2-ethynyl-9-[(S)-2-methylbutoxycarbonyllcarbazole (1), 3-ethynyl-9-[(S)-2-methylbutoxycarbonyl]carbazole (2), 2-ethynyl-9-[(S)-2-methylbutyl]carbazole (3), and 2-ethynyl-9-[(S)-4-methylhexyl]carbazole (4) were synthesized and polymerized with [(nbd)RhCl](2)-Et3N. The corresponding polyacetylenes with number-average molecular weights ranging from 68,700 to 310,000 were obtained in good yields. Poly(1) exhibited a large specific rotation and an intense Cotton effect in toluene, indicating that it formed a helix with predominantly one-handed screw sense, while the other three polymers showed no evidence for taking a helical structure. Poly(1) largely decreased the CD intensity upon heating from -10 to 60 degrees C. Poly(1) showed a Cotton effect in film state in a manner similar to solution state. No chiral amplification was observed in the copolymerization of 1 with achiral 2-ethynyl-9-tert-butoxycarbonylcarbazole (5). (c) 2007 Wiley Periodicals, Inc.