Synthesis of Heterotelechelic α,ω Dye-Functionalized Polymer by the RAFT Process and Energy Transfer between the End Groups

The synthesis of a vinyl polymer with two different fluorescent dye end groups using reversible addition−fragmentation chain transfer (RAFT) polymerization is described. Use of a pentafluorophenyl (PFP) activated ester chain transfer agent (CTA) provided a polymer with an α end group that was reactive toward amines and a dithioester ω end group. The α PFP ester was amidated with Oregon Green Cadaverin. This did not harm the ω dithioester, which was subsequently aminolyzed with an excess of <i>n</i>-propylamine in the presence of Texas Red-2-sulfonamidoethyl methanethiosulfonate, resulting in a disulfide bond connecting the second dye to the polymer chain. Excess dyes and side products were removed by thin layer chromatography (TLC). Gel permeation chromatography (GPC) using a UV−vis detector could verify the presence of each dye on the polymer chain and the absence of free dyes. The synthesis of the polymer by a living radical technique and the mild complementary conjugation methods conducted after polymerization at each end group allowed to introduce complex dye residues possessing high brightness and photostability. In particular, fluorescent dyes capable of acting as donor and acceptor for electronic excitation energy transfer were chosen. Time-resolved fluorescence measurements were used to determine the time constant of energy transfer between the end groups of isolated polymer chains. Assuming a Förster-type process, an average end-to-end distance of 4.5 nm was calculated, which was in reasonable agreement with data obtained from light scattering.