Synthesis, characterization, and optical properties of ROMP copolymers with pendant carbazole and coumarin groups

Two series of random copolymers containing at the same time two fluorescent groups, carbazole and coumarin, linked to a poly(norbornene dicarboximide) backbone have been prepared by controlled ring-opening metathesis polymerization (ROMP), promoted by Grubbs' third generation catalyst (G3). The relative amount of the two functionalities was systematically varied along the copolymer chain, and the high degree of structural control observed allowed also for the preparation of a block copolymer with an equimolar content of fluorophore groups. In comparison to the related homopolymers, all the random copolymers exhibited in solution typical photoluminescence due to the carbazole or coumarin moiety, together with fluorescence arising from the energy transfer from the donor carbazole groups to the acceptor coumarin groups. This energy transfer seems to occur through intramolecular interactions, as it is not observed in the block copolymer and in the 50/50 homopolymer blend. On the other hand, in the solid state also the energy transfer from carbazole to coumarin through interchain interactions can take place. Of note, moving from solution to solid state fluorescence analysis, a blue shift of the band related to the energy transfer phenomenon is observed. This finding could be related to a combined effect of energy and electron transfer from donor to acceptor.