Synthesis and Characterization of IR-783-SH Cyanine Dye

The heptamethine cyanine dye IR783, which has minimal cell toxicity^{37 (link)}, was purchased from Sigma-Aldrich (St. Louis, MO, USA). To a solution of IR-783 (250 mg, 0.33 mmol) in 6 mL of anhydrous DMF, 3-mercaptopropionic acid (40.7 μL, 0.467 mmol) and triethylamine (65.3 μL, 0.467 mmol) were added. The green solution was stirred in the dark at room temperature. The reaction was complete after 21 h, as monitored through high-performance liquid chromatography (HPLC). A green solid was isolated through precipitation with 4 °C ether and was washed with cold ether (3 mL). The precipitate was dissolved in water and dried in vacuum ¹H NMR (300 MHz, CD₃OD) results were as follows: δ 8.89 (d, 2H, J = 14.2 Hz), 7.49 (d, 2H, J = 7.4 Hz), 7.41 (t, 2H, J = 7.6 Hz), 7.34 (d, 2H, J = 7.8 Hz), 7.25 (t, 2H, J = 7.5 Hz), 6.32 (d, 2H, J = 14.3 Hz), 4.19 (t, 4H, J = 6.7 Hz), 3.06 (t, 2H, J = 7.0 Hz), 2.90–2.87 (m, 4H), 2.70 (t, 4H, J = 5.9 Hz), 2.56 (t, 2H, J = 6.9 Hz) 2.00–1.92 (m, 10H), and 1.76 (s, 12H). HRMS-ESI [M]⁻m/z for C₄₁H₅₁N₂O₈S₃ 795.2959 was calculated to be 795.5.