Synthesis and properties of polyacetylenes with salicylideneaniline groups

Acetylenes containing salicylideneaniline groups-N-salicylidene-3-ethynylaniline (1), N-(3-t-butylsalicylidene)-3-ethynylaniline (2), and N-(3-t-butylsalicylidene)-4-ethynylaniline (3)-polymerized smoothly and gave yellow to red polymers in excellent yields when a rhodium catalyst was employed. Polymers with alkyl substituents on the aromatic rings [poly(2) and poly(3)] were soluble in CHCl₃, tetrahydrofuran, and so forth, whereas the polymer without alkyl substituents [poly(1)] was insoluble in any solvent. N-(3-t-Butylsalicylidene)propargylamine did not provide any polymer. Thermogravimetric analyses of the resultant polymers exhibited good thermal stability (T_o, onset temperature of weight loss > 300°C). The ultraviolet-visible spectra of the polymers showed absorption maxima and cutoff wavelengths around 360 and 520 nm, respectively. The polymers exhibited largely Stokes-shifted fluorescence (emission wavelength ≃ 550 nm) upon photoexcitation at 350 nm, which resulted from the photoinduced intramolecular proton transfer.