A novel near-infrared colorimetric probe for fluoride anions based on a heptamethine dye†
A near-infrared heptamethine indocyanine probe was successfully synthesized and demonstrated to be a colorimetric and fluorescent probe for F− with high selectivity and sensitivity. In the presence of F−, the probe shows a new prominent absorption peak at 942 nm, accompanied by a remarkable solution color change from pale red to colorless in a few seconds, which provides a way for the ‘naked-eye’ detection of fluoride anions. These responses were attributed to the deprotonation of the –NH fragment of an indolyl unit, and the 1H NMR study and density functional theory (DFT) calculations are in agreement with them. Moreover, the probe can be employed to detect F− quantitatively within a certain concentration range, and the limit of detection could be as low as 1.3 μM.