A squaraine-based colorimetric and F− dependent chemosensor for recyclable CO2 gas detection: highly sensitive off–on–off response

Abstract

An unsymmetrical squaraine-based chemosensor SH₂ has been synthesized, and its sensing behavior towards CO₂ gas was described in detail by UV-vis and ¹H NMR spectroscopies in DMSO. The results indicated that the extremely sensitive “naked-eye” CO₂ gas detection can be operated in the presence of excess [Bu₄N]F (TBAF) and the sensor is easy to recycle. These properties enable SH₂ to act as a CO₂ and F⁻ controlled “OFF–ON–OFF” switch. Combining theoretical analyses, a plausible sensing mechanism was proposed to illustrate how the receptor SH₂ works as a CO₂ sensitive and selective colorimetric probe in the present system.