Syntheses and nonlinear optical behavior of four-arm star-shaped phthalocyanine indium polymers containing azobenzene

In this report, a series of novel four-arm star-shaped polymethyl methacrylate with core of phthalocyanine indium polymers (InPc-(PMMAx)4) were achieved with different molecular weights through Activator ReGenerated by Electron Transfer Atom Transfer Radical Polymerization, using the synthesized phthalocyanine indium (InPc-Br) as initiator. The InPc-(PMMAx)4 polymers were characterized by NMR, FT-IR, GPC, UV–Vis and PL spectroscopy. The nonlinear optical (NLO) properties of InPc-(PMMAx)4 polymers were investigated by the Z-scan technique and it revealed that InPc-(PMMA16)4 obtained satisfactory NLO properties with imaginary third order susceptibility (Im[χ(3)]) of 16.4 × 10−12 esu. Furthermore, reacting polymer InPc-(PMMA16)4 with NaN3 and 1-(4-nitrophenyl)-2-(4-(prop-2-yn-1-yloxy) phenyl) diazene (Azo-yne) through click reaction, a novel InPc polymer InPc-(PMMA16-b-Azo)4 was successfully synthesized. InPc-(PMMA16-b-Azo)4 displayed a weak fluorescence at 707 nm compared to InPc-(PMMA16)4, demonstrating the energy transfer (ET) process between Azo and InPc, which could be proved by density functional theory. Because of the ET process, InPc-(PMMA16-b-Azo)4 exhibited a better NLO performance than InPc-(PMMA16)4, with Im[χ(3)] of 20.7 × 10−12 esu. In addition, the InPc-(PMMA16-b-Azo)4/PMMA complexes were prepared for the convenience of practical application, and it exhibited an excellent Im[χ(3)] value of 30.2 × 10−12 esu and a satisfactory limiting threshold of 0.04 J/cm2. The significantly enhanced NLO properties of InPc-(PMMA16-b-Azo)4/PMMA complexes demonstrate a weaker aggregation effect in polymethyl methacrylate matrix than in methyl methacrylate solution. Our study provides a promising design strategy to synthesize high performance NLO materials for practical applications.