Synthesis and Optical Properties of Fluorescent Switchable Silica Nanoparticles Covered with Copolymers Consisting of Diarylethene and Fluorene Derivatives

摘要

abstract_textpSilica nanoparticles covered with random copolymers consisting of diarylethene monomer (DE) and fluorene monomer (FL) (SNP-poly(DE-co-FL)) were designed and synthesized by reversible addition-fragmentation chain transfer (RAFT) copolymerization of DE and FL initiated from a RAFT agent immobilized on the surface of silica nanoparticle. SNP-poly(DE-co-FL) and silica-free polymer (poly(DE-co-FL)), which are soluble in tetrahydrofuran, underwent reversible photoisomerization of DE moieties upon alternating irradiation with ultraviolet and visible light. They exhibited fluorescence ON/OFF switching between fluorescence ON state of FL in the open-ring form of DE and fluorescence OFF state by an efficient Forster/fluorescence resonance energy transfer from the excited FL not only in the same polymer chain but also in the surrounding polymer chains to the closed-ring form of DE. Diarylethenefluorene dyad (DE-FL) was synthesized to compare with fluorescence ON/OFF switching efficiencies of SNP-poly(DE-coFL) and poly(DE-co-FL). The closed-ring isomers of DE in DE-FL, poly(DE-co-FL), and SNP-poly(DE-co-FL) were found to quench fluorescence of 0.78, 6.3, and 15.6 FL moieties, respectively. Thus, fluorescence switching efficiency of SNP-poly(DE-co-FL) was 2.5 times higher than poly(DE-co-FL) and 20 times higher than DE-FL. Furthermore, the closed-ring isomer of DE in SNPpoly( DE-co-FL) was found to quench 6.3 FL moieties in the same polymer chain and 9.3 FL moieties in four polymer chains in the neighborhood./p/abstract_text