Pyrene based chemosensor for carbon dioxide gas – Meticulous investigations and digital image based RGB analysis

Highlights

• Simple sonochemical synthesis of pyrene Schiff base chemosensor (KB-4).

• Dual sensing of Fluoride and Carbon dioxide (CO₂) gas through optical means (colorimetry and fluorimetry).

• Fluoride induced CO₂ sensing with a detection limit of 0.1 ml.

Abstract

A new pyrene Schiff base (KB-4) was synthesized and demonstrated as simple colorimetric chemosensor for carbon dioxide (CO₂) gas activated by fluoride anion. The chemical structure of KB-4 was validated through pivotal characterization methods. A combined quantum chemical calculations and spectroscopic techniques were adopted to understand the photophysical properties of KB-4. The sensitivity of KB-4 chemosensor towards various anions is investigated and showed excellent selectivity towards F⁻ anion with a distinct color change. The mechanism of F⁻ anion sensing is due to the complete deprotonation of –NH proton in KB-4 as revealed by ¹H NMR titration studies as well as DFT calculations. Subsequently, the in-situ deprotonated KB-4 is employed for CO₂ gas sensing. Interestingly, deprotonated KB-4 is responded instantaneously to CO₂ gas by exhibiting significant colorimetric and fluorimetric changes with a detection limit of 0.4 ml. Further, digital image based RGB analysis using smartphone is introduced for detection of CO₂ gas. The digital images of CO₂ gas induced fluorimetric changes are captured using smartphone and the RGB analysis of the images are processed using MATLAB. The intensity variation in the color components as an indicative measure for detection of CO₂ gas is demonstrated.