The synthesis and spectral properties of a stimuli-responsive D–π–A charge transfer dye based on indole donor and dicyanomethylene acceptor moiety

A dual mode chemosensor dye 3 for detection of fluoride ion, based on the D–π–A molecular framework by one-step condensation, presents high selectivity and sensitivity both in colorimetric and fluorometric analyses. Upon the addition of F− anion, the absorption band shows a remarkable red shift along with fluorescent intensity decreasing. The absorption and fluorescent intensities of the dye 3 can be reversibly selected by deprotonation/protonation of the amine moiety via control of intramolecular charge transfer (ICT), leading to a molecular switch with “on” and “off” states. 1H NMR titration analysis and DMol3 calculation were employed to reveal the intermolecular charge transfer system of dye 3–F− complex.

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► The F− selective dye 3 based on D–π–A framework is synthesized.
► Colorimetric and fluorometric analyses of dye 3 upon addition of F− are described.
► F− ions can interact with dye 3 forming anion–dye adducts.
► The pH stimuli-responsive property of dye 3 is determined.