Synthesis of Optically Active Poly(<i>m</i>‑phenyleneethynylene–aryleneethynylene)s Bearing Hydroxy Groups and Examination of the Higher Order Structures

Abstract

Novel optically active poly­(<i>m</i>-phenyleneethynylene–aryleneethynylene)­s bearing hydroxy groups with various arylene units {poly­[(<i>S</i>)-/(<i>R</i>)-<b>1</b>–<b>3a</b>]–poly­[(<i>R</i>)-<b>1</b>–<b>3e</b>] and poly­[(<i>S</i>)-<b>2</b>–<b>3a</b>]} were synthesized by the Sonogashira–Hagihara coupling polymerization of 3,5-diiodo-4-hydroxy-C₆H₄CONHCH­(CH₃)­COXC₁₂H₂₅ [(<i>S</i>)-/(<i>R</i>)-<b>1</b> (X = O), (<i>S</i>)-<b>2</b> (X = NH)] with HCC–Ar–CCH [<b>3a</b> (Ar = 1,4-C₆H₄), <b>3b</b> (Ar = 1,4-C₆H₄-1,4-C₆H₄−), <b>3c</b> (Ar = 1,4-C₆H₄-1,4-C₆H₄-1,4-C₆H₄−), <b>3d</b> (Ar = 2,5-dihexyl-1,4-C₆H₂), <b>3e</b> (Ar = 2,5-didodecyl-1,4-C₆H₂)]. The yields and number-average molecular weights of the polymers were in the ranges 60–94% and 7,000–29,500 with no correlation between the yield and the <i>M</i>_n. Circular dichroism (CD), UV–vis, and fluorescence spectroscopic analyses indicated that poly­[(<i>S</i>)-<b>1</b>–<b>3a</b>]–poly­[(<i>S</i>)-<b>1</b>–<b>3c</b>] and poly­[(<i>S</i>)-<b>2</b>–<b>3a</b>] formed predominantly one-handed helical structures in THF, while poly­[(<i>S</i>)-<b>1</b>–<b>3d</b>] and poly­[(<i>S</i>)-<b>1</b>–<b>3e</b>] showed no evidence for forming chirally ordered structures. All polymers emitted blue fluorescence. The solution state IR measurement revealed the presence of intramolecular hydrogen bonding between the amide groups at the side chains of poly­[(<i>S</i>)-<b>1</b>–<b>2a</b>]. The helical structures and helix-forming abilities of the polymers were analyzed by the molecular mechanics (MM), semiempirical molecular orbital (MO) and density functional theory (DFT) methods. Tube-like structures, presumably formed by perpendicular aggregation of the helical polymers, were observed by atomic force microscopy (AFM)