Multistimuli-Responsive Luminescence Switching of Pyrazine Derivative Based Donor-Acceptor-Donor Luminophores

Three symmetrical donor-acceptor-donor (D-A-D) luminophores (C1, C2, and C3) with pyrazine derivatives as electron-withdrawing groups have been developed for multistimuli-responsive luminescence switching. For comparison, reference compounds R1 and R2 without the pyrazine moiety have also been synthesized. Intramolecular charge transfer (ICT) interactions can be found for all D-A-D luminophores owing to the electron-withdrawing properties of the two imine nitrogen atoms in the pyrazine ring and the electron-donating properties of the other two amine nitrogen atoms in the two triphenylamine units. Moreover, luminophores C1, C2, and C3 exhibit on-off-on luminescence switching properties in mixtures of water/tetrahydrofuran with increasing water content, which is different from the on-off switching for typical aggregation-caused quenching (ACQ) materials and off-on switching for traditional aggregation-induced emission (AIE) materials. Additionally, upon grinding the pristine samples, luminophores C1, C2, and C3 display bathochromically shifted photoluminescence maxima that can be recovered by either solvent fuming or thermal annealing treatments. The piezofluorochromic (PFC) properties are more pronounced than those for reference compounds R1 and R2, which indicates that D-A molecules have the ability to amplify the PFC effect by tuning the ICT interactions upon tiny structural changes under pressure. Furthermore, the target luminophores demonstrate acid-responsive photoluminescence spectra that can be recovered in either basic or ambient environments. These results suggest that D-A complexes are potential candidates for multistimuli-responsive luminescence switching because their ICT profiles can be facilely tuned with tiny external stimuli.