Improvement of the thermal stability of near-infrared-absorbing heptamethinecyanine dyes by anion-exchange from an iodide to fluorine-containing anions

• NIR-absorbing dyes with fluorine-containing anions have been synthesized.
• The prepared NIR-absorbing dyes showed lower oxidation potentials.
• The prepared NIR-absorbing dyes showed better thermal stability.

Anion exchange in a near-infrared-absorbing heptamethinecyanine dye from an iodide to fluorine-containing anions proceeded smoothly at room temperature to give the corresponding heptamethinecyanine dyes carrying bis(trifluoromethanesulfonyl)imide ((CF3SO2)2N−), hexafluorophosphate (PF6−) and trifluoromethanesulfonate (CF3SO3−) in good yields. Heptamethinecyanine dyes carrying (CF3SO2)2N−, PF6−, and CF3SO3− showed better thermal stabilities than the dye carrying an iodide as a counter anion.

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