Highly Fluorescent Benzophosphole Oxide Block-Copolymer Micelles

The efficient synthesis
of highly fluorescent para-biphenyl-substituted benzophospholes
via zirconium-mediated metallacycle
transfer is reported. A norbornene-appended benzophosphole oxide monomer
was found to readily undergo living ring-opening metathesis polymerization
with the Grubbs third-generation catalyst to yield either a homopolymer
or block copolymers. The resulting block copolymers consisting of
lipophilic alkylated- or pinacolboronate-capped comonomers undergo
self-assembly into spherical micelles in tetrahydrofuran/hexanes mixtures,
as determined by dynamic light scattering and transmission electron
microscopy. One hallmark of the benzophosphole-containing polymers
is their greatly enhanced emission intensity in solution in relation
to their monomers, presumably due to a restriction in molecular motion
upon formation of homopolymers or assembled block-copolymer micelles.
Evidence for “analyte amplified precipitation” was found,
wherein addition of a substoichiometric amount of fluoride to a benzophosphole
oxide–pinacolboronate block-copolymer spherical micelle leads
to rapid precipitation of highly emissive aggregates. This observation
should guide the development of related methods to visually detect
(and sequester) analytes in solution.