Synthesis and nonlinear optical properties of polyacetylenes containing oxadiazole and thiophene pendant groups with high thermal stability

A series of random copolymers poly(3-ethynylthiophene)-copoly(2-(4- decyloxyphenyl)-5-(4-ethynylphenyl)-1,3,4-oxadiazole) with different oxadiazole content (P2-P4) and homopolymer poly(3-ethynylthiophene) (P1) as well as poly(2-(4-decyloxyphenyl)-5-(4-ethynylphenyl)-1,3,4-oxadiazole) (P5) were prepared. The copolymers (P2-P4) are completely soluble in common organic solvents. The structures and properties of all polymers were characterized and evaluated by FTIR, ¹H NMR, ¹³C NMR, TGA, UV, PL, GPC, and nonlinear optical (NLO) analyses. The incorporation of diaryl-oxadiazole into polyacetylene-containing thiophene significantly endows copolymers with higher thermal stability, which may origin from the synergetic effect of the "jacket effect" of diaryl-oxadiazole units and the effect of retarding or eliminating a few 6-electrocycliaztion proceeds of oxadiazole-containing polyacetylene due to the hindrance of thiophene units. When the copolymer (P3) posses more regular alternating thiophene pendants and oxadiazole pendants arrangement along the polymer backbone, it shows good thermal stability (T _d up to 388 °C) and larger third-order nonlinear optical susceptibility (I(3) up to 11.0×10^-11 esu).