Synthesis of acceptor-donor-acceptor based phenothiazine-5-oxide aldehydes displaying large Stokes shift- “on-off-on” acidofluorochromic switch and molecular logic gate operation

• Synthesis of novel A-D-A type push–pull phenothiazine- 5 -oxide scaffolds end-capped with formyl groups. • Intermolecular D-A interactions observed in crystal packing arrangement. • Reversible acidofluorochromism observed in solution as well as solid state. • Investigation of reversible acidofluorochromism and site of protonation by NMR and DFT studies. • Filter paper strips fabricated for volatile acid sensing. • IMPLICATION logic gate operation with TFA and TEA as two inputs. A series of A-D-A type of push pull molecules based on phenothiazine- 5 -oxide appended with the p -formylphenyl group at 3- and 7- positions was synthesized in moderate to good yields. Single crystal X-ray diffraction (XRD) studies of two A-D-A molecules revealed intermolecular D-A interactions in the molecular packing. A positive solvatochromism was observed with large Stokes shifts. These fluorescent solids showed “on–off-on” response toward TFA (trifluoroacetic acid) vapors, which was reversed in the presence of TEA (triethylamine) vapors. A similar response was also observed in solution. NMR and DFT studies were conducted to explore the interactions between phenothiazine- 5 -oxide dialdehydes and TFA. Filter paper strips for TFA sensing were also fabricated. These compounds are found to exhibit IMPLICATION logic gate operation with TFA and TEA as the inputs.