Controllable synthesis of iridium(iii)-based aggregation-induced emission and/or piezochromic luminescence phosphors by simply adjusting the substitution on ancillary ligands

Abstract

Three multifunctional cationic iridium(III)-based materials with aggregation-induced emission (AIE) and piezochromic luminescence (PCL) behavior have been rationally designed with the help of the theoretical calculations and successfully synthesized. All complexes contain the same cyclometalated ligand, 1-(2,4-difluorophenyl)-1H-pyrazole (dfppz), while functionalized ancillary ligands with different substitution are used to control their photophysical properties. Complex 1 and 2 with ancillary ligands modified with aliphatic chains and carbazole end-capped alkyl groups, respectively, undergo remarkable and reversible changes in emission color in the solid state upon grinding or heating. In addition, 2, characterized as having the 3ILCT excited-state feature, simultaneously exhibits an interesting AIE behavior, showing almost non-emission in good solution but enhanced emission in its solid state. Further modification of 2 by attachment of a tert-butyl group on the ligand obtains complex 3, an amorphous material, which only displays AIE activity. More importantly, with the merits of reversible PCL and AIE properties of 2, the rare multi-channel color change and temperature-dependent emission behavior of the iridium(III) complex have been observed. Furthermore, the emissive nanoaggregates of 2 can be efficiently quenched by picric acid, making it a highly sensitive chemosensor for explosives, which is demonstrated in iridium(III)-based luminescent materials for the first time.