Energy-level tuning of poly(p-phenylenebutadiynylene) derivatives by click chemistry-type postfunctionalization of side-chain alkynes

A series of poly(p-phenylenebutadiynylene) polymers substituted with electron-rich alkynes as the side chain were synthesized by homocoupling polymerization of asymmetric bifunctional monomers. The electron-rich alkynes underwent “click chemistry” with tetracyanoethylene (TCNE) to produce donor-acceptor chromophores. Optical and electrochemical characterizations clearly indicated that the energy level and band gap of P2 could be precisely controlled by the addition of acceptor molecules. One of the most important conclusions of this study is that a linear relationship between the lowest occupied molecular orbital (LOMO) and the amount of TCNE was observed. From the Z-scan measurement, all the compounds exhibited very special nonlinear optical properties, which suggested a tendency to transfer from saturable absorption (SA) to reverse saturable absorption (RSA).