Triarylborane-functionalized polynorbornenes: Direct polymerization and signal amplification in fluoride sensing

The vinyl-addition homo- and copolymerization of a norbornene monomer bearing an electron-deficient triarylborane side group (M1) using Pd(II) catalyst in the presence of the 1-octene chain transfer agent efficiently produced a novel class of soluble polynorbornenes functionalized with triarylborane groups. The catalytic system provided high-molecular-weight polymers (Mw > 200 × 103 g/mol) with high thermal stability (Td5 = 240–390 °C) depending on the M1 content. Characterization by multinuclear NMR spectroscopy revealed the formation of vinyl-type polynorbornes with a controlled amount of M1 and the presence of a base-free tricoordinate boron center. While UV–vis absorption and PL spectra of the polymers displayed almost identical absorption and emission features to those of M1, indicating the absence of intramolecular aggregation or excimer formation in both the ground and excited states, the homopolymer showed enhanced fluorescence quenching efficiency in the sensing of fluoride anions in comparison with M1. Moreover, a positive correlation between the fluorescence quenching efficiency and the content of borane moiety in the polymer chain was observed for the polymers.