Tetrazole functional copolymers: Facile access to well-defined Rhenium(I)-Polymeric luminescent materials

Abstract

Well-defined random copolymers containing tetrazole functional groups were prepared by a combination of reversible addition-fragmentation chain transfer (RAFT) radical homopolymerisation of pentafluorophenyl acrylate (PFPA), end-group modification and post-polymerisation modification of the activated ester side-groups with primary amines. PolyPFPA with a size exclusion chromatography (SEC) measured Mn of 10,800 and dispersity, Ð, of 1.05 was prepared with 2-cyano-2-propyl benzodithioate as the RAFT chain transfer agent and 2,2′-azobisisobutyronitrile (AIBN) as the source of primary radicals in 1,4-dioxane. Prior to modification of the pentafluorophenyl (PFP) ester side-groups, the thiocarbonylthio end-group was removed via a radical-mediated desulfurisation employing two equivalents of AIBN. Complete removal of the end-group was successful as judged by UV–vis spectroscopy with no effect on the molecular weight distribution of the parent homopolymer based on SEC analysis. The pendent PFP ester groups were subsequently modified in a sequential manner with n-butylamine and 5-aminotetrazole yielding the corresponding random amide species quantitatively, as judged by 19F NMR and FTIR spectroscopies, and of varying molar composition as determined by 1H NMR spectroscopy. The reaction of the tetrazole functional copolymers with Re(CO)3(phen)Br (phen = 1,10-phenanthroline) yielded the corresponding rhenium-polymer hybrids via coordination through the pendent tetrazole functional group. Successful, and quantitative coordination was confirmed by FTIR spectroscopy and detailed photophysical studies. In the case of the latter, the absorption profiles of all hybrid materials possessed broad bands centred around ca. 370 nm associated with metal-to-ligand charge transfer (MLCT) transitions; excitation as this wavelength results in a broad emission centred at 606 nm for all hybrid species and is due to emission from the triplet MLCT excited states.