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

Abstract

AbstractSilica 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 Förster/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. Diarylethene‐fluorene dyad (DE‐FL) was synthesized to compare with fluorescence ON/OFF switching efficiencies of SNP‐poly(DE‐co‐FL) 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 SNP‐poly(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.