Guest induced morphological transformation from nanospheres to nanowires by hydrogen bond self-assembly

Phosphorescent nanospheres of a carboxyl-functionalized iridium complex ([Ir(ppy)2(Hdcbpy)], ppy: 2-phenylpyridine; Hdcbpy: 4-carboxy-2,2'-bipyridyl-4'-carboxylate) were prepared by a conventional precipitation method. Driven by hydrogen bond interaction between carboxylic groups of the complex and the guest molecule tris(imidazoline), these nanospheres can be transformed into 1-dimensional nanowires in the presence of tris(imidazoline) at the concentration of the iridium complex higher than 4.8 mM, while nanowires change back to nanospheres with the diameter obviously smaller than that of the sole complex of [Ir(ppy)2(Hdcbpy)]. The interaction between carboxylic groups and tris(imidazoline) molecules was confirmed by FT-IR spectra. The structures of the nanowires and nanospheres were further studied by XRD diffraction analysis. With the morphological transformation from nanospheres to nanowires, the phosphorescence of nanostructures was blue shifted from 590 to 564 nm.