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

An unsymmetrical squaraine-based chemosensor SH2 has been synthesized, and its sensing behavior towards CO2 gas was described in detail by UV-vis and (1)H 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.