Synthesis and properties of helical polyacetylenes containing carbazole

Novel acetylene monomers containing carbazole with chiral menthyl and bornyl groups, 9-(1R,2S,5R)-menthyloxycarbonyl-2-ethynylcarbazole (1), 9-(1S,2R,5S)-menthyloxycarbonyl-2-ethynylcarbazole (2), 9-(1R,2S,5R)-menthyloxycarbonyl-3-ethynylcarbazole (3) and 9-(1S)-bornyloxycarbonyl-2-ethynylcarbazole (4) were synthesized and polymerized with a Rh catalyst to give the corresponding polymers [poly(1)-poly(4)] with moderate M_n value of (11.5-92.2) × 10³ in good yields (77-89%). CD spectroscopic studies revealed that poly(1), poly(2) and poly(4) took predominantly one-handed helical structure in CHCl₃, THF, toluene, and CH₂Cl₂, while poly(3) did not. Addition of methanol to CHCl₃ solutions of poly(1) and poly(2) resulted in the formation of aggregates showing smaller CD signals at 275 and 320 nm. The helical structure of poly(1) and poly(2) was very stable against heating. The polymers emitted fluorescence in 0.40-2.90% quantum yields. Poly(4) exhibited an obvious oxidation peak at 1.10 V. The polymers were thermally stable below 300 °C.