Developing anisotropic force-induced hypso- and bathochromic bidirectional fluorescence switches based on...

The development of anisotropic force-triggered three-color fluorescence switches, especially those featuring with hypso- and bathochromic bidirectional fluorescence changings, is a highly important and rather challenging topic. Herein, four fluorene- or anthracene-based luminogens, decorating with pyrene units as steric hindrance modulators, are elaborately synthesized and categorized into two groups: Group 1 (2Py-1-Fl and 2Py-2-Fl) and Group 2 (4Py-1-An and 4Py-2-An). Specifically, the two fluorogenic compounds of Group 1 possessing two pyrene units exhibit rare hypsochromic and bathochromic bidirectional mechanofluorochromic characteristics, while the two luminogens with greater steric hindrance in Group 2 demonstrate conspicuous two-color fluorescence changes under mechanical stimulation. Therefore, by meticulously changing the number of pyrene units to regulate molecular steric hindrance, anisotropic force-dependent fluorescence responses of luminogens with a fluorene or an anthracene core were effectively manipulated. Furthermore, based on its high-contrast tricolored mechanofluorochromism exhibited by 2Py-1-Fl, an advanced information encryption system is successfully constructed.