Syntheses and characterizations of Zn (Ⅱ) Phthalocyanines & Naphthopyrans based polymers for improved nonlinear optical properties

Abstract

In this paper, four organic polymers of poly [(MMA)x-co-(NPMA)y-co-(CPMA)z] and four zinc phthalocyanine (ZnPc) polymers of poly [(MMA)x-co-(NPMA)y-co-(ZnPc)z] have been successfully synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization, where MMA is methyl methacrylate, NPMA is 3,3-diphenyl-8-methacryloxy-3H-naphtho [2,1-b]pyran, and CPMA is 3,4-dicyanophenyl methacrylate. The components of these polymers have been fully characterized by 1H and 13C NMR, FT-IR, Raman, XPS, UV–Vis, and photoluminescence (PL) spectroscopy. From PL spectra, poly [(MMA)x-co-(NPMA)y-co-(ZnPc)z] polymers display strong fluorescence quenching by the energy transfer (ET) process between NPMA and ZnPc moieties. The third-order nonlinear optical (NLO) properties of poly [(MMA)x-co-(NPMA)y-co-(ZnPc)z] polymers have been investigated by the Z-scan technique, and poly [(MMA)168-co-(NPMA)5.2-co-(ZnPc)1.2] (Q4) showed the best NLO properties owing to the much stronger ET between NP and ZnPc units. Furthermore, it is essential to obtain doped poly (methyl methacrylate) (PMMA) films for practical application. The poly [(MMA)168-co-(NPMA)5.2-co-(ZnPc)1.2]/PMMA film exhibited a higher nonlinear absorption coefficient of 61 × 10−11 m/W and a lower limiting threshold of 0.19 J/cm2. The significantly enhanced NLO properties of poly [(MMA)168-co-(NPMA)5.2-co-(ZnPc)1.2]/PMMA film compared with solution are attributed to the weaker aggregation effect in PMMA film. This research provides a promising molecular design strategy for high performance NLO materials.