Azine based AIEgens with multi-stimuli response towards picric acid†
Multifunctional aggregation induced emission luminogens (AIEgens) are novel materials which have significant applications in various fields including biomedical, optoelectronics and sensors. Enormous efforts have been directed towards the strategic development and characterisation of AIEgens, in order to better understand the AIE mechanism. Herein, we studied the photophysical properties of symmetrical azine (D–π–D) based AIEgens in detail by varying the solvent polarity and viscosity. The AIE behaviour of the azine derivatives relies on the substituents on the nitrogen atom of the amine moiety. Further, these azine derivatives sense the picric acid (PA) with high selectivity and sensitivity in both monomer and aggregated forms. The hydrogen bonding interaction of PA with any one side of the amine nitrogen leads to the formation of a new intramolecular charge transfer state which results in the formation of new absorption and emission spectra. Interestingly in the presence of PA, azine monomers exhibit fluorescence enhancement in pure THF, while aggregated azine molecules show fluorescence quenching in THF–water mixtures.