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

Abstract

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.