•A polyether bridged fluorescent probe of Pb2+ has been designed and synthesized.•The sensing mechanism is based on coordination induced disaggregation of squaraine.•The probe showed high selectivity and sensitivity.•The binding mode has been discussed.In this work, a novel fluorescent chemosensor, based on a polyether bridged squaraine, has been developed for the detection of Pb2+, and gives excellent sensitivity and selectivity using a cation-induced disaggregation strategy. This probe exhibited a specific “turn on” fluorescent response to Pb2+ with a detection limit of 1.70 × 10−8 M, and the identification for Pb2+ was not impacted by competing ions such as Na+, Li+, K+, Mg2+, Ca2+, Sr2+, Co2+, Ni2+, Zn2+, Ag+, Cd2+, and Hg2+. Due to the high binding ability of the polyether bridged ionophore toward Pb2+, the disaggregation process could be trigged by the formation of squaraine-Pb2+ complex, resulting in a fast fluorescent release. The sensing mechanism has been confirmed by NMR, IR, and dynamic light scattering experiments. Further research shows that this novel fluorescent probe can be applied in the fast detection of Pb2+ in urine and shrimp samples.Figure optionsDownload full-size imageDownload as PowerPoint slide

The formation of a 1:2 inclusion complex between adamantyl tethered squaraine and β-cyclodextrin inhibited the aggregation of SQ in aqueous solution, enhancing the fluorescent emission of the near-infrared dye. The resulting SQ⊂β-CD complex serves as a sensitive fluorescent probe for imaging intracellular pH in living cells.

Due to the high affinity between dithiocarbamate (DTC) and Hg2+, a fluorescent probe based on squaraine chromophore with DTC side arm for Hg2+via coordination induced deaggregation signaling has been designed and synthesized. Squaraine has a high tendency to aggregate in aqueous solution, and such self-aggregation usually results in a dramatic absorption spectral broadening with fluorescence emission quenching. The combination of the DTC side arm of the probe with Hg2+ induces steric hindrance, leading to the deaggregation of the dye complex, companying with a fluorescence emission restoration. In EtOH–H2O (20:80, v/v) solution, this “turn on” fluorescent probe has high selectivity and sensitivity toward Hg2+ over other metal ions, and the limit of detection for Hg2+ was estimated as 2.19 × 10−8 mol/L by 3σ/k.A squaraine based “turn on” fluorescent probe with a dithiocarbamate ionophore for mercury ion was described, and the sensing mechanism was based on coordination induced deaggregation.

•A novel ratiometric near-infrared fluorescent probe (SQ-1) for Zn2+ has been first synthesized based on squaraine dye.•SQ-1 can detect Zn2+ in acetone by a 22 nm red-shift and a remarkable enhancement of the fluorescence intensity.•The detection identification for Zn2+ will not be impacted by the biologically ubiquitous ions such as Na+, K+, Mg2+ and Ca2+.A squaraine based ratiometric near-infrared fluorescent probe with bipyridyl binding arms for Zn2+ (SQ-1) has been designed and synthesized. SQ-1 exhibits a selective fluorogenic response to Zn2+ in acetone by a 22 nm red-shift and a remarkable enhancement of the fluorescence intensity. Further study shows that the calculated detection limit for Zn2+ is 6.1 × 10−8 M (3σ/k) and the identification for Zn2+ will not be impacted by competing ions such as Na+, K+, Mg2+, Ca2+, Pb2+, Mn2+, Ba2+ and Hg2+. The binding mode between SQ-1 and Zn2+ has also been discussed.

•A squaraine based sensor for chromo-fluorogenic detection of cysteine was reported.•The detection limit for cysteine was 36.7 nM.•A dynamic measuring range could be obtained by adjusting the concentration of Hg2+.•The binding mechanism has also been discussed.A novel squaraine derivative (SQ-1) was synthesized and characterized for the determination of cysteine. Binding with Hg2+ as a fluorescent quencher to SQ-1 leads to absorption and emission turn-off. More significantly, the SQ-1–Hg2+ complex exhibits a dual-channel chromofluorogenic responses to biologically important cysteine with a high sensitivity and selectivity over other natural amino acids, along with a low detection limit of 36.7 nM.Graphical abstract

A novel unsymmetrical squaramide-linked squaraine dye (SQ) has been synthesized through squaramide 3 and semisquaraine 6. The molecular structure of SQ has been characterized by 1H NMR, IR and MS. Due to the influence of the hydrogen bond and the solvent effect, SQ exhibits unique spectral properties compared with typical squaraine dyes. For its excellent ability of binding primary amine, SQ is a promising receptor of recognizing primary amine.

A novel squaraine-based chemosensor SQ-1 has been synthesized, and its sensing behavior toward various metal ions was investigated by UV−vis and fluorescence spectroscopies. In AcOH−H2O (40:60, v/v) solution, Hg2+ ions coordinate with SQ-1 causing a deaggregation which induces a visual color and absorption spectral changes as well as strong fluorescence. In contrast, the addition of other metals (e.g., Pb2+, Cd2+, Cu2+, Zn2+, Al3+, Ni2+, Co2+, Fe3+, Ca2+, K+, Mg2+, Na+, and Ag+) does not induce these changes at all. Thus SQ-1 is a specific Hg2+ sensing agent due to the inducing deaggregation of the dye molecule by Hg2+.

A novel chemosensor based on unsymmetrical squaraine dye (USQ-1) for the selective detection of Hg2+ in aqueous media is described. USQ-1 in combination with metal ions shows dual chromogenic and “turn-on” fluorogenic response selectivity toward Hg2+ as compared to Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Al3+, Cu2+, Cd2+, Mn2+, Fe3+, Ag+, Pb2+, Zn2+, Ni2+ and Co2+ due to the Hg2+-induced deaggregation of the dye molecule. A recognition mechanism based on the binding mode is proposed based on the absorption and fluorescence changes, 1H NMR titration experiments, ESI-MS study, and theoretical calculations.

A novel squaraine dye (SQ) modified by ferrocene has been synthesized through (E)-1-dodecyl-2-ferrocenyl vinyl-1H-pyrrole and squaric acid. The molecular structure of SQ was characterized by 1H NMR, 13C NMR, MS and elemental analysis. SQ is high soluble in common solvents. The maximum absorptions of SQ in different solvents are in the range of 708−734 nm, exhibiting positive solvatochromism with increasing solvent polarity. The optical and electrical properties of SQ indicate that it is a promising electron donor material for bulk-heterojunction organic solar cell.

A novel chemosensor based on unsymmetrical squaraine dye (USQ-1) for the selective detection of Hg2+ in aqueous media is described. USQ-1 in combination with metal ions shows dual chromogenic and “turn-on” fluorogenic response selectivity toward Hg2+ as compared to Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Al3+, Cu2+, Cd2+, Mn2+, Fe3+, Ag+, Pb2+, Zn2+, Ni2+ and Co2+ due to the Hg2+-induced deaggregation of the dye molecule. A recognition mechanism based on the binding mode is proposed based on the absorption and fluorescence changes, 1H NMR titration experiments, ESI-MS study, and theoretical calculations.