Electrospinning composite fibers doped with rhenium complex: Preparation, characterization and photophysical feature comparison

In the present paper, a diamine ligand possessing an electron-pulling group 2-phenyl-5-(pyridin-2-yl)-1,3,4-oxadiazole (denoted as PPYO) and its corresponding Re(I) complex Re(CO)3(PPYO)Br were synthesized and carefully characterized. The geometric structure of Re(CO)3(PPYO)Br was analyzed by its single crystal XRD. Theoretical calculation on the crystal suggested that the first few electronic excitations owned a mixed character of metal-to-ligand-charge-transfer (MLCT) and ligand-to-ligand-charge-transfer (LLCT). By doping Re(CO)3(PPYO)Br into a polymer host of poly(vinylpyrrolidone) with electrospinning technique, composite fibers were yielded. The photophysical feature comparison between bulk samples and composite fibers was performed, which suggested that both face-to-face π-π attraction in crystal and the immobilization in PVP matrix could repress the MLCT excited state geometric relaxation, leading to improved emissive parameters including emission blue shift, longer excited state lifetime and better photostability.