Synthesis of water-soluble red-emitting thienyl-BODIPYs and bovine serum albumin labeling.

The synthesis of three red-emitting and water-soluble thienyl-BODIPYs has been achieved. The trimethyl(propargyl)ammonium group was chosen as a vector for water solubility. One or two cationic arms were introduced either on the 2-position of the thienyl unit or on the 4-position on the boron atom. These dyes have pronounced absorption around 600 nm and intense emission at 650 nm with quantum yield of about 60% in water. Grafting of such BODIPYs via a flexible arm to BSA is very efficient, allowing attachment of 1 to 30 labels in a controlled manner. Very strong fluorescence (quantum yield 56%)without aggregation of the dye at a low loading ratio (1:5 BSA/label) in PBS buffer is measured.