Highly sensitive colorimetric and fluorometric anion sensors based on mono and di-calix[4]pyrrole substituted diketopyrrolopyrroles

• Four novel anion sensors developed by coupling calix[4]pyrrole with diketo pyrrolopyrrole.
• The sensors show colorimetric as well as fluorometric behaviour towards selective ions.
• The sensors could detect the anion concentration of 1.15 and 0.025 ppm by colorimetry and fluorometry respectively.

Four novel deeply coloured and highly fluorescent anion sensors have been developed by coupling calix[4]pyrrole with two different diketopyrrolopyrroles. The sensors showed both colorimetric and fluorometric sensitization by selective anions. Complexation properties of the receptors with anions like halides, acetate, phosphate, sulphate, hydrogen sulphate, perchlorate and cyanide were investigated by UV–vis spectroscopy and fluorescence spectroscopy. Sharp visual colour changes as well as complete fluorescence quenching was observed in the presence of selective anions like fluoride, acetate, phosphate and cyanide. Visual detection of sensing properties was achievable up to anion concentration of 1.15 ppm for detection in visible light and 0.025 ppm under UV light. One of the sensor, namely S1, showed a dramatic colour change in the presence of CN− ion. Furthermore, a cheap and highly efficient procedure for bulk scale synthesis of monoiodo-octamethylcalix[4]pyrrole, which is one of the main building blocks for the design of calix[4]pyrrole based sensors has been developed.

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