Study on polymer fibers doped with phosphorescent Re(I) complex via electrospinning: synthetic strategy, structure, morphology and photophysical features.

In the following paper, a Re(I) complex with electron-withdrawing oxadiazole group in its diamine ligand (denoted as N-N) was synthesized. Its single crystal structure analysis confirmed the successful synthesis of both ligand and complex. The central Re(I) ion localized in a traditional octahedral coordination environment. The diamine ligand 2-(pyridin-2-yl)-5-(p-tolyl)-1,3,4-oxadiazole (denoted as PPOZ) took a coplanar structure and the corresponding face-to-face π-π attraction between PPOZ ligands made the Re(I) complex molecules adjust a highly ordered arrangement which was positive to improve emissive performance. In order to repress the excited state geometric relaxation and further improve the emissive performance, the Re(I) complex was doped into a polymer host poly(vinylpyrrolidone) via electrospinning, resulting in composite fibers. The morphology of those composite fibers was analyzed by electron microscopy. The photophysical comparison between bulk sample and composite fibers indicated that the composite fibers showed emission blue shift, longer excited state lifetime and improved photostability. Further analysis suggested that the excited state geometric relaxation could be effectively repressed when the Re(I) complex molecules were immobilized in the polymer matrix, leading to above variations.