Functional disubstituted polyacetylenes and soluble cross-linked polyenes: Effects of pendant groups or side chains on liquid crystallinity and light emission of poly(1-phenyl-l-undecyne)s

A group of new poly(1-phenyl-1-undecyne)s with different mesogenic and chromophoric pendant groups or side chains were successfully synthesized and the structural variations were found to greatly affect the mesomorphic and luminescent properties of the polymers. The 1-phenyl-1-undecyne monomers (C ₆H₅C≡C(CH₂)₉OCOR with R = C₆H₄-C₆H₁₀-C₅H ₁₁ (1), C₆H₄-OCO-C_{6 4}-OC₆H₁₃ (2), and C₆H ₄-C≡C-C₆H₄-OC₇H₁₅ (3) were prepared by simple esterification and/or coupling reactions. The polymerizations of 1-3 were effected by WCl₆-Ph₄Sn in toluene at 60-80°C, giving polymers with high molecular weights in good isolation yields. The structures and properties of the polymers were characterized and evaluated by GPC, IR, NMR, TGA, DSC, POM, XRD, UV, and PL analyses. The polymerizations of 1 and 2 yield linear poly(1-phenyl-1-alkyne)s P1 and P2, respectively, while that of 3 gives a nonlinear macromolecule with its poly(1-phenyl-1-alkyne) main chain cross-linked by the oligo-(diphenylacetylene) side chains resulted from the partial polymerization of its diphenylacetylene pendants (P3x). All the polymers are completely soluble in common solvents and are thermally stable with T_d ≥ 390°C. Polymers P1 and P2 undergo nematic and smectic transitions at ∼100 and ∼170°C, respectively, while P3x is nonmesomorphic. Upon excitation, the poly(1-phenyl-l-alkyne) chains of P1 and P2 emit a strong blue light of 460 nm, with their fluorescence quantum efficiencies comparable to or higher than that of poly(1-phenyl-1-octyne), a highly emissive disubstituted polyacetylene. Polymer P3x emits a blue-green light of 490 nm, due to the energy transfer from its poly(1-phenyl-1-octyne) main chain to its oligo(diphenylacetylene) side chains.