Novel Malachite Green- and Rhodamine B-labeled cationic chain transfer agents for RAFT polymerization

Two novel cationic RAFT agents have been synthesized, one labeled with a Malachite Green (MG) dye and another with a Rhodamine B (RhoB) dye. MG-labeled dithiobenzoate (MGEDBA) was prepared in a straightforward manner after synthesis of MG-ethylammonium chloride that reacted with a precursor dithiobenzoate bearing an activated ester function. However, the analogous reaction with RhoB amino derivative led to a mixture of dithiobenzoate and thioamide derivatives. An alternative approach yielded the RhoB-labeled RAFT agent (RhoBEDBA) with complete conversion. The purification of these dye-labeled RAFT agents was very challenging because of their dual nature (aromatic and ionic). Both MGEDBA and RhoBEDBA were efficient RAFT chain transfer agents to control the polymerization of N,N-dimethylacrylamide (DMA). The resulting α-end-labeled MG- and RhoB-PDMA samples presented low dispersities (Đ<1.2) and both chain-ends were preserved. Finally, we showed that the attachment of RhoB and MG to the PDMA polymer chain-end did not influence the photophysical properties of these dyes. Therefore, these new dye-labeled RAFT agents can be used to prepare various labeled polymers and especially water-soluble ones, to study their conformation and dynamics in solution or at interfaces using fluorescence methods, or as labeled probes for imaging and/or diagnosis purposes.