Background: Visual pH sensors have received significant attention in the fields
of environmental monitoring, analytical chemistry, food safety, and biomedicine. Therefore,
a single organic moiety showing both naked-eye and fluorescence sensing of pH change is
rare and in higher demand.
Objective: A novel phenothiazine-based Schiff base PTz-SB was synthesized via facile organic
transformations. This molecule showed promising naked-eye and on-spot pH sensing
application, both using UV-visible and fluorescence techniques.
Methods: The novel phenothiazine-based Schiff base was synthesized via facile organic
transformation. The Schiff base was applied for both naked eye and fluorescence sensing of
pH, using UV-visible and fluorescence techniques, respectively.
Results: A Redshifts of 27 nm and 80 nm were observed in the λmax of absorption and emission
spectra, respectively, on changing the pH from 12.2 to 1. The naked-eye pH sensing
may be attributed to the change in colour from blue (higher pH) to dark green (lower pH),
under daylight conditions. Furthermore, the change in fluorescence spectra is more pronounced.
The fluorescence colour of the compound changes from dark blue to green and then
finally to orange, on changing the pH from 12.2 to 4 to 1.5, respectively. Moreover, the electrochemical
studies of the Schiff base were also procured. The bandgap obtained from the cyclic
voltammetry studies was found to be 2.04 eV, which is characteristic of green emission.
Conclusion: The easily synthesizable novel Schiff base can be utilized for real-life, on-spot
practical application of pH sensing, which does not require sophisticated analytical instruments.
Moreover, the time and cost of detection of pH using this thermally robust Schiff
base are also very promising.