Development of a push–π–pull phenothiazine‐vinyl‐isophorone fluorophore: a novel solvatochromic and pH indicator

Abstract

Knoevenagel condensation of phenothiazine‐3,7‐dicarbaldehyde with an isophorone yielded a new phenothiazine derivative (PTZ‐c) fluorophore. The solvatochromic and pH‐sensing abilities of PTZ‐c, an asymmetric fluorophore with a single isophorone molecule, were shown to be exceptional. PTZ‐c produced very delicate absorbance and emission spectra. When the polarity of the solvent was increased, the PTZ‐c emission spectra showed greater sensitivity than the absorption spectra. Multiple spectroscopic techniques, including Fourier transform infrared spectroscopy, nuclear magnetic resonance, and mass spectrometry, were used to characterize the manufactured PTZ‐c sensor. To demonstrate the beneficial solvatochromic behaviour associated with intramolecular charge transfer, the absorption spectra of the synthesized DA PTZ‐c dye were analyzed in different solvents of varying polarity. Band intensity and the wavelength of PTZ‐c emission were also found to be highly solvent dependent. It was observed that when solvent polarity was increased to a maximum of 4122 cm−1, Stokes’ shift also increased. To analyze the Stokes' shift that depended on the solvent, a linear correlation between solvation and energy was used. An investigation of PTZ‐c quantum yield (ф) was also conducted. Both the absorbance and fluorescence spectra of the sensor in dimethylformamide as a function of pH were studied. A fluorescence peak was seen at 562 nm, whereas the greatest absorption wavelengths were found at 403 and 317 nm. It was shown that the pH‐sensing mechanism depended on protons removed from the PTZ‐c chromophore, which caused a colour shift and variation in both emission and colorimetric properties.