Polynorbornene copolymers with pendent o-carborane and carbazole groups: Novel side-chain donor-acceptor copolymers for turn-on sensing of nucleophilic anions

Vinyl-type polynorbornene copolymers with side-chain o-carborane (1-phenyl-o-carborane for P1-P3; 1-methyl-o-carborane for P4) and carbazole moieties were produced by vinyl addition copolymerization of norbornene monomers using a Pd(II) catalyst in combination with 1-octene chain transfer agent. The catalytic system provided well-defined copolymers with controlled incorporation of monomers. The copolymers possessed high thermal stability with high decomposition (Td5 > 410 °C) and glass transition temperatures (Tg > 350 °C). Treatment of the closo-copolymers (P1-P4) with excess KOH in refluxing EtOH/THF led to degradation of the closo-carborane cage to produce nido-copolymers (nido-(P1-P4)). While P1-P3 exhibited a weak carbazole-based fluorescence, the corresponding nido-copolymers gave rise to a 2.0-3.6-fold increase in PL intensity depending on the comonomer content. An electrochemical study and comparative PL results of P4 and nido-P4 suggest that photoinduced charge transfer from carbazole donors to 1-phenyl-o-carborane acceptors was responsible for the weak fluorescence of P1-P3.