Synthesis and characterization of polymers containing in the chain backbone carbazoles substituted with two acceptor groups as nonlinear optical chromophores

Polymers containing in the chain backbone carbazoles substituted with two acceptor groups as nonlinear optical chromophores have been synthesized from 3,6-diformyl-9-heptylcarbazole and bis(cyanoacetate) by the Knoevenagel polycondensation. A one-stage polycondensation was carried out in tetrahydrofuran (THF) solution to yield a carbazole main-chain polymer with low molecular weight in low yield. A two-stage polycondensation first carried out in THF and followed by a solid-state polycondensation yielded a carbazole main-chain polymer with high molecular weight in high yield. Thin films of polymers with good optical quality could be obtained from their chloroform solutions by spin-coating. After electric poling, the films exhibited reasonable second-order nonlinear optical responses and the large off-diagonal tensor components.