ROMP of norbornene and oxanorbornene derivatives with pendant fluorophore carbazole and coumarin groups

Abstract

A series of new (oxa)norbornene dicarboximide monomers, decorated with carbazole and coumarin as pendant fluorophore groups, were synthesized and characterized. Their behaviour in ring-opening metathesis polymerization (ROMP) was explored in the presence of commercial Grubbs’ third generation catalyst G3 and cis-selective catalyst GZ. Norbornene dicarboximide (NDI) monomers were successfully polymerized by both the catalysts, while oxanorbornene dicarboximide (ONDI) analogues showed scarce reactivity toward polymerization promoted by GZ. The nature of the spacer (ethylene or p-xylene) between the NDI unit and the chromophore seems to not affect the outcome of the polymerization. Moving from G3 to GZ, it was possible to synthetize NDI-based polymers with cis-olefin content increasing from 47 to 89%, depending on the nature of the pendant fluorophore group. The obtained polymers showed photoluminescence in solution and solid state owing to the carbazole or coumarin fragment, regardless of the nature of the spacer and cis-olefin amount. Interestingly, a significant excimer emission due to the overlap of carbazole groups was observed for a carbazole-functionalized polymer film, as a result of the combined effect of two factors, the stiffness of the spacer (p-xylene) linking the NDI moiety to the fluorophore and the high stereoregularity degree (83% cis) of the main chain.