Covalent-linked porphyrin-based polymer/multi-walled carbon nanotube nanohybrids: Synthesis and enhanced nonlinear optical performance

In this paper, a series of novel porphyrin-based polymers named poly(6-(5'-(4′-phenoxyl)-10′,15′,20′-triphenylporphyrin) methacrylate)n with different molecular weights and functional alkyne end-groups (PPorx-C≡CH) were successfully synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization. Furthermore, the corresponding multi-walled carbon nanotube (MWCNT) nanohybrids PPorx-MWCNTs were prepared by reacting PPorx-C≡CH with MWCNT-N3 through click reaction. PPorx-MWCNT exhibited obvious fluorescence quenching at 652 and 725 nm compared to PPorx-C≡CH, demonstrating the photo-induced electron transfer (PET) process between PPorx and MWCNT, which was proved by photo-electrochemical experiments. After covalent-linked with MWCNT, PPorx-MWCNT show an enhanced NLO performance (the third order optical susceptibility (Im[χ(3)]) = 4.93 × 10−11 esu) compared to PPorx-C≡CH in N,N-dimethylformamide (DMF) solution, causing by the PET process. In order to enhance the practicality of PPorx-MWCNT, the PPorx-MWCNT/polymethyl methacrylate (PPorx-MWCNT/PMMA) composites were prepared. Among them, PPor3-MWCNT/PMMA showed the best NLO performance (Im[χ(3)] = 5.58 × 10−11), with a limiting threshold of 0.98 J/cm2. Compared with methyl methacrylate (MMA) system, the weaker aggregation effect in PMMA matrix contributes to enhance the NLO properties of PPorx-MWCNT. Our study has opened a new path for the development of high performance NLO materials for practical applications.