Amino methoxy difluoroboron diketonate as a multicolor and multi-responsive polymorphic fluorescence emitter

We here report the synthesis and stimuli-responsive fluorescence nature of amino-methoxy-difluoroboron diketonate, DFB-NH2, which was prepared via the Curtius rearrangement to introduce a primary amine on the phenyl ring. Thanks to the NH2 group, the molecule exhibits intramolecular charge transfer (ICT) nature in the ground state of the solution and crystalline phases. We observed a quinoid-like structure and a typical head-to-tail H-type dimer structure in the crystal state. The single crystal with dark-red weak emission demonstrates a blue-shifted emission after mechanical smearing, as a unique mechanofluorochromism (MFC). The drop-casted sample on a paper sheet also demonstrates significant MFC. Additionally, characteristic acid-/base-responsivity is observed in the solution phase, polymer-dispersed films, and powder samples.