An iridium complex-based phosphorescent probe for recognition to bisulfite and cyanide in neutral aqueous system

•A new iridium complex was successfully synthesized.•In aerated PBS buffer, bisulfite and cyanide can be easily discriminated by the different phosphorescent colors of the complex.•The reaction between the complex and HS− could be attributed to 1,4-addtion rather than 1,2-addition.

A newly designed cyclometalated iridium complex Ir(mepi)(ppy)2 (2, Hppy = 2-phenylpyridine, Hmepi = 3,3-dimethyl-1-ethyl-2-(4-(pyridin-2-yl)styryl)indolium iodide (1)) was successfully synthesized for the rapid detection of HSO3− and CN−. For complex 2, it is interesting that the selective 1,4-addition reaction with HSO3− in aerated DMSO/PBS buffer can be visualized by intense turn-on green emission. However, the 1,2-addition reaction with CN− resulted in an emission color change from colorless to orange-yellow. Furthermore, the limits of detection for HSO3− and CN− were calculated as low as 0.049 and 0.15 μM, respectively. The results indicate that the two anions can be detected selectively and separately by naked-eyes in neutral aqueous system. As the typical interfering anion for detecting HSO3−, HS− led to the almost similar emission change that was caused by HSO3−. As a result, the reaction between 2 and HS− could be assigned as 1,4-addition rather than 1,2-addition reaction, which was further confirmed by the 1H NMR spectra changes of the ligand with these representative anions (HSO3−, HS− and CN−).

Graphical abstractA newly designed cyclometalated iridium complex Ir(mepi)(bpy)2+ (bpy = 2,2′-bipyridine, Hmepi = 3,3-dimethyl-1-ethyl-2-(4-(pyridin-2-yl)styryl)indolium iodide) was successfully synthesized for the rapid detection of HSO3− and CN− in aerated DMSO/PBS buffer. It is interesting that the addition of bisulfite to the buffer results in an intense turn-on green emission due to the 1,4-addition reaction, while an orange-yellow emission caused by cyanide was observed due to the 1,2-addition reaction. The green emission for the ensemble of the complex and HS− is almost similar to that of bisulfite indicated that the reaction between the complex and HS− can be assigned as 1,4-addition reaction rather than 1,2-addition. All these results were further confirmed by the characteristic data for reactions between the ligand (Hmepi) with these anions. Moreover, the limits of detection for HSO3−, HS−and CN− were calculated as low as 0.049, 0.30 and 0.15 μM, respectively. Filter paper test exhibited that these anions can be detected selectively and separately by naked-eyes.Figure optionsDownload full-size imageDownload high-quality image (105 K)Download as PowerPoint slide