Synthesis of the end-functionalized polymethyl methacrylate incorporated with an asymmetrical porphyrin group via atom transfer radical polymerization and investigation on the third-order nonlinear optical properties

A novel asymmetrical zinc(II) porphyrin (ZnPor-Br) was synthesized as the initiator for the atom transfer radical polymerization (ATRP). Using CuBr/2,2′-dipyridyl as the catalyst system, the ATRP of polymethyl methacrylate (PMMA) was carried out to afford a new linear PMMA with the end group of the asymmetrical porphyrin (ZnPor-PMMA). The structures of the porphyrin, ZnPor-Br and as-prepared polymer were determined by FT-IR, 1H NMR spectra and further confirmed by element analysis. Polydispersity index (PDI) obtaining from the gel permeation chromatograph (GPC) indicated that the molecular weight distribution was narrow, and the whole process of polymerization was well controlled. The third-order nonlinear optical properties of polymers were investigated by using Z-scan technique in the pico-second time scale. The nonlinear refracting index (n2) and the third-order nonlinear polarizability [χ(3)] were 4.1 × 10−10 esu and 1.64 × 10−10 esu respectively, while the molecular polarizability (γ′) was 1.01 × 10−28 esu (Mn = 2000). The obtained results implied that the prepared compound featured the large nonlinear optical limiting properties and could serve as a potential candidate for the reverse saturable absorption (RSA) and the refractive-based optical limiting applications in the laser protection field.