A series of AB2-type second-order nonlinear optical (NLO) polyaryleneethynylenes: using different end-capped spacers with adjustable bulk to achieve high NLO coefficients

Abstract

In this article, according to the concept of “suitable isolation group”, four new polyaryleneethynylenes containing azo-chromophore moieties derived from the same AB₂-type monomer were prepared through a typical Sonogashira reaction successfully, in which different isolation groups in different size (from H to carbazole) were introduced to the periphery of the hyperbranched polymers as end-capped moieties via highly efficient “click chemistry” reaction under copper(I) catalysis. Due to the different end-capped groups, these hyperbranched polymers (P1–P4) exhibited different NLO properties accordingly, realizing the adjustment of the properties of hyperbranched polymers through the structural design. Among them, P4, with carbazole as “suitable isolation group”, demonstrated the best performance with the SHG coefficient of 113.8 pm V⁻¹ and the onset temperatures for decays in d₃₃ value (T_onset) of 132 °C.