Dynamic Hydrogen-Bonding Switching Enables Crystal Transformation for Multi-Stimuli Responsive Fluorescence

Controlling solid-state structural transitions in organic cocrystals to achieve stimulus-responsive luminescence remains an ongoing challenge. Herein, we have developed a series of cocrystal systems exhibiting reversible crystal transformation and stimulus-responsive luminescence via a dynamic hydrogen-bond switching strategy. Three conformationally adaptive V-shaped molecules (26PY, 35PY, and 13PH) serve as both hydrogen-bonding and electron donors. Oxygen-containing solvents (H₂O, DMF, DMSO) merely act as hydrogen-bond acceptors, while 1,2,4,5-tetracyanobenzene (TCNB) or 1,5-dinitrobenzene (DNB) function as both hydrogen-bonding and electron acceptors. Mechanical grinding of solid mixtures composed of electron donors and acceptors in weakly polar solvents allowed the donor to rapidly capture water, yielding a blue-emitting hydrated intermediate. Thermal dehydration then triggered conformational adjustment of the donor, promoting binary cocrystal formation through newly established hydrogen bonds between electron donors and acceptors. Furthermore, the electron donor and acceptor can directly interact with DMF or DMSO to form a ternary cocrystal instead of forming hydrated crystals, as stronger hydrogen bonds are formed. More interestingly, the donor can also form cocrystals with many nitroaromatic compounds to exhibit dynamic fluorescence. Finally, we demonstrated the applicability of these cocrystals in sensing and multi-level anti-counterfeiting. This work opens up new avenues for the development of stimulus-responsive cocrystals for smart materials.