•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−).A 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.Download high-res image (106KB)Download full-size image

Bisulfite, as an important additive in foodstuffs, is one of the most widely distributed environmental pollutants. The excessive intake of bisulfite may cause asthmatic attacks and allergic reactions. Therefore, the determination and visual detection of bisulfite are very important. Herein, a newly designed hydrophilic indolium cycloruthenated complex, [Ru(mepbi)(bpy)2]+ [1; bpy = 2,2′-bipyridine and Hmepbi = 3,3-dimethyl-1-ethyl-2-[4-(pyridin-2-yl)styryl]benzo[e]indolium iodide (3)], was successfully synthesized and used as a bisulfite probe. The bisulfite underwent a 1,4-addition reaction with complex 1 in PBS buffer (10 mM, pH 7.40), resulting in a dramatic change in absorption spectra with a red shift of over 100 nm and a remarkable change in solution color from yellow to pink. It is worth noting that this obvious bathochromic shift is rarely observed in the detection of bisulfite through an addition reaction. The detection limit was calculated to be as low as 0.12 μM by UV–vis absorption spectroscopy. Moreover, complex 1 was also used to detect bisulfite in sugar samples (granulated and crystal sugar) with good recovery.

The pH-dependent reversible cyclometallation and reactions with nitrite in a near-aqueous system of a related set of cyclometallated ruthenium(II) bipyridyl complexes were investigated in detail. These complexes are [Ru(ppy)(bpy)2]PF6 (1, bpy = 2,2′-bipyridine, Hppy = 2-phenylpyridine), [Ru(thpy)(bpy)2]PF6 (2, Hthpy = 2-(2-thienyl)pyridine), and [Ru(dfppy)(bpy)2]PF6 (3, Hdfppy = 2-(2,4-difluorophenyl)pyridine). As expected, reversible UV–Vis spectra of these three complexes in near-aqueous solutions can be achieved by treating with acid or base, which indicates a pH-dependent reversible cyclometallation. However, the addition of nitrite to acidic solutions of these complexes disturbed the reversible pH-dependent processes. Unexpected ruthenium complexes in the aforementioned system were then isolated and characterized using FT-IR, MS, 1H NMR, and UV–Vis spectra, indicating that two reaction modes occurred at the ruthenium(II) centers: (1) the insertion of NO into the ruthenium–aryl bond to form a ruthenium C-nitroso complex; and (2) the coordination of NO with the entire dissociation of one bipyridine to form a {Ru–NO}6 complex, which is the first example involving the cleavage of Ru–N∧N bonds in ruthenium bipyridyl complexes.

•A mercuric ensemble based on a cycloruthenated complex was obtained for detecting I− in water.•It exhibit remarkable color change from yellow to red with the detection limit of 0.77 μM.•The test strips with the ensemble for tracing I− were practically realized.A new water-soluble cycloruthenated complex Ru(bthiq)(dcbpy)2+ (1, Hbthiq = 1-(2-benzo[b]thiophenyl)isoquinoline, dcbpy = 4,4′-dicarboxylate-2,2′-bipyridine) was designed and synthesized to form its mercuric ensemble (1-Hg2+) to achieve visual detection of iodide anions. The binding constant of 1-Hg2+ is calculated to be 2.40 × 104 M−1, which is lower than that of HgI2. Therefore, the addition of I− to the aqueous solution of 1-Hg2+lead to significant color changes from yellow to deep-red by the release of 1. The results showed that iodide anions could be easily detected by the naked eyes. The detection limit of iodide anion is calculated as 0.77 μM. In addition, an easily-prepared test strip of 1-Hg2+ was obtained successfully to detect iodide anions.

•A cycloruthenated complex with an aldehyde was successfully synthesized and characterized.•It exhibited a blue-shift above 130 nm in its MLCT absorption peak upon mixing with HSO3−.•It can serve as a “naked-eye” indicator for HSO3− in water.A new hydrophilic cyclometallated ruthenium complex 1 (Ru(pba)(bpy)2+, Hpba = 4-(2-pyridyl)benzaldehyde, bpy = 2,2′-bipyridine) was successfully synthesized. The as-prepared complex exhibited typical MLCT absorptions centered at 536 nm, which are assigned to Ru-bpy CT transitions and noticeably red-shifted relative to Ru(bpy)32+ derivatives because of the formation of Ru–C bond. In view of a possible adduct of aldehyde and bisulphite, its performance to recognize HSO3− ions was investigated in details. Upon addition of bisulphite, the maximum of MLCT absorptions was blue-shifted to 400 nm, accompanied with an apparent color change from red to yellowish. However, there were no obvious changes observed in MLCT bands upon addition of other common anions, cysteine and homocysteine. The results showed that this cycloruthenated complex displayed high selectivity to bisulphite, which can be detected with the naked-eye. The detection limit of the chemo-sensor for bisulphite reached 2.73 μmol/L.A new cyclometallated ruthenium complex with 4-(2-pyridyl)benzaldehyde as CˆN-ligand was successfully synthesized and characterized. The existence of an aldehyde made the complex sensitive and selective to bisulphite anions in aqueous buffered solutions with the color change from deep-red to yellowish. And the detection limit for bisulphite is 2.73 μmol/L.

•A cyclometalated iridium complex 1 with indolium block was synthesized.•It displayed high sensitivity and selectivity to bisulfite in HEPES buffer.•The in situ generated 1-SO3H system can selectively detect Cu2 + by naked eyes.A cyclometalated iridium complex (1) with indolium block was synthesized successfully and then used as a colorimetric probe for bisulfite in CH3CN-HEPES (v/v, 2:98) buffer system with the detection limit as low as 0.15 μM. It is interesting that the in situ generated 1 − SO3H system demonstrated sequential recognition to Cu2 +, along with the solution color recovering from colorless to light-yellow. The apparent solution color changes displayed that the complex 1 can be used to detect bisulfite and Cu2 + by naked eyes.A newly designed iridium complex [Ir(mepi)2bpy)]3 + (1) with indolium block was successfully used as a colorimetric probe for bisulfite in CH3CN-HEPES buffer system (v/v, 2:98). It is interesting that the in situ generated 1-SO3H system demonstrates sequential recognition to Cu2 +, along with the solution color recovering from colorless to light-yellow. The apparent solution color changes displayed that the complex 1 can be used to detect bisulfite and Cu2 + by naked eyes.

The pH-dependent reversible cyclometallation and reactions with nitrite in a near-aqueous system of a related set of cyclometallated ruthenium(II) bipyridyl complexes were investigated in detail. These complexes are [Ru(ppy)(bpy)2]PF6 (1, bpy = 2,2′-bipyridine, Hppy = 2-phenylpyridine), [Ru(thpy)(bpy)2]PF6 (2, Hthpy = 2-(2-thienyl)pyridine), and [Ru(dfppy)(bpy)2]PF6 (3, Hdfppy = 2-(2,4-difluorophenyl)pyridine). As expected, reversible UV–Vis spectra of these three complexes in near-aqueous solutions can be achieved by treating with acid or base, which indicates a pH-dependent reversible cyclometallation. However, the addition of nitrite to acidic solutions of these complexes disturbed the reversible pH-dependent processes. Unexpected ruthenium complexes in the aforementioned system were then isolated and characterized using FT-IR, MS, 1H NMR, and UV–Vis spectra, indicating that two reaction modes occurred at the ruthenium(II) centers: (1) the insertion of NO into the ruthenium–aryl bond to form a ruthenium C-nitroso complex; and (2) the coordination of NO with the entire dissociation of one bipyridine to form a {Ru–NO}6 complex, which is the first example involving the cleavage of Ru–N∧N bonds in ruthenium bipyridyl complexes.