Highly sensitive fluorescence response of [2.2]paracyclophane modified D−A type chromophores to trace water, pH, acidic gases and formaldehyde

Abstract

Donor (D)−acceptor (A) type compounds have drawn significant attraction recently due to their large Stokes shifted emission and easy-tunable emissive behaviour. Herein, a new family of D−A type [2.2]paracyclophanyl 4H-pyran-4-one fluorescent molecules (3a−3d) have been rationally designed and easily synthesized, and they exhibited intensity and wavelength-based fluorescence sensing in response to active hydrogen, polarity, viscosity and acidic/basic vapours. Therefore, visual and quantitative detection of trace water in different organic solvents with low detection limits of 1.39–8.75 ppm were achieved for 3c; Fluorescence ratiometric detection of pH in the range of 2–7 was achieved for 3b. Moreover, 3a−3d could be served as coated test strips for detecting acidic gases (HCl, TFA, HCOOH and SO2) and HCHO with high sensitivity, reversibility, reproducibility and long-time stability. The response times to TFA vapour were 3–5 s, to HCOOH vapour were 5–7 s and to HCHO vapour 32–70 s. These processes could be readily visualized by unaided eye detection under day light and UV-irradiation. Furthermore, the sensing mechanisms were elucidated by X-ray diffraction, NMR and TD-DFT calculations. The present results suggest that the coated test strips of 3a−3d have potential applications in data encryption and decryption and anti-counterfeiting fields.