•We synthesized a ratiometric pH probe base on dicyanomethylene-4H-chromene..•We firstly reported pyrrolidine had a dual roles in this Knoevenagel condensation.•This probe showed high selectivity and sensitivity for pH variation (pH=2.44–6.00).•The probe was stable in the studied solvent within one month at room temperature.We report here a ratiometric pH probe (Z)−2-(2-(2-(4-hydroxyphenyl)−2-(pyrrolidin-1-yl)vinyl) −4H-chromen-4-ylidene)-malononitrile over the pH range of 2.44–6.00. It was synthesized by Knoevenagel Reaction from dicyanomethylene-4H-chromene and pyrrolidine. This is the first example of pyrrolidine as a part of the product structure in Knoevenagel condensation. High selectivity and sensitivity for pH variation were observed with significant fluorescent ratiometric responses and a remarkable Stokes shift (about 138 nm). The probe was stable in the studied solvent and no obvious fluorescence changes were detected in acidic media within one month at room temperature.Download high-res image (151KB)Download full-size image

•Ratiometric & reversible fluorescence probe for NaCN detection.•Low detection limit (1.8 × 10−9 mol L−1) for CN− detection.•High sensitivity and selectivity for CN− detection.•Experimental results are consistent with theoretical calculations.A novel compound 1 based on phenanthro[9,10-d]imidazole platform has been unveiled as an effective ratiometric fluorescent probe for selective and rapid detection of NaCN. The sensing behavior was demonstrated by UV-vis, fluorescence experiments and NMR studies. This sensory system exhibited prominent visual emission color change toward CN− over other testing anions in CH3CN-PBS buffer (v/v, 3:1, pH 7.2) solution, with a 1:1 binding stoichiometry. Detection limit of the new cyanide-sensing probe 1 was 1.8 × 10−9 mol L−1, which was much lower than the World Health Organization (WHO) recommended level drinking water. The experimental results revealed that the formation of anionic species from the deprotonation of imidazole moiety by the CN− ion was responsible for the spectral changes. Calculations of the transition energies also verified such process. The spectral responses of probe could be switched back and forth alternatively by adding CN− and H+ anions into the CH3CN-PBS buffer (v/v, 3:1, pH 7.2) solution, which indicated that compound 1 was stable and could be used in reversible manner.Download high-res image (157KB)Download full-size image

A diketopyrrolopyrrole-based fluorescent probe 1 was explored as a ratiometric probe for selective detection of Au3+, with the detection limit of 18 nM. The probe displayed an absorption maximum at 528 nm and a strong red fluorescence at 610 nm. In the presence of Au3+, the absorption and emission band blueshifted to 488 and 555 nm, respectively. Correspondingly, the color of the probe solution changed from orange to flesh color, and the fluorescence changed from orange to yellow-green. NMR and HRMS spectral analysis demonstrated that the selective ratiometric fluorescence response of probe 1 with Au3+ involved a selective Au3+-mediated hydrolyzation and oxidization reactions using a catalytic amount of Au3+. In addition, the ratiometric response of probe 1 was rationalized by DFT and TDDFT calculations.

A diketopyrrolopyrrole-based fluorescent probe DPP-HBT bearing a benzothiazole hydrazone motif exhibited an obvious fluorescent turn-on response toward Pb2+ ions with a low detection limit of 2.3 × 10−10 M in aqueous solution. Furthermore, the imaging experiments indicated that this probe was cell-permeable and could be used to detect Pb2+ ions within living cells.