Highly water-soluble neutral near-infrared emissive BODIPY polymeric dyes

Abstract

Three highly water-soluble near-infrared emissive polymeric BODIPY dyes (polymers A–C) were prepared by the palladium-catalyzed Suzuki polymerization of highly water-soluble 2,6-diiodo-3,5-distyryl-BODIPY dyes with 1,4-phenyldiboronic acid and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-di[1-[2-(2-methoxyethoxy)ethoxy]ethyl]fluorene, respectively. Partial replacement of fluorine subunits of BODIPY cores at 4,4-positions of polymer C with ethynyl subunits resulted in a highly water-soluble BODIPY polymeric dye (polymer D). Polymers A–D show solubility of at least 20 mg mL⁻¹ in aqueous solution. For comparison purposes, polymers E and F were prepared by palladium-catalyzed Sonogashira polymerization of highly water-soluble 2,6-diiodo-3,5-distyryl-BODIPY dye with highly water-soluble 1,4-diethynylbenzene and 2,6-diethynyl BODIPY dye bearing branched oligo(ethylene glycol)methyl ether residues, respectively. Upon comparison, polymer E shows low solubility in aqueous solution (0.1 mg mL⁻¹), whereas polymer F is almost insoluble in aqueous solution (less than 0.05 mg mL⁻¹), but both are soluble in organic solvents such as chloroform, DMSO and DMF (at least 10 mg mL⁻¹).