Synthesis and characterization of a series of Ru(II) complexes and their electrospinning polymer fibers: Photphysical comparison between binuclear and mononuclear Ru(II) complexes and spectral response towards O2 gas

Abstract

As a class of typical metal complexes, luminescent Ru(II) complexes with diamine ligands have drawn much research attention for the application of optoelectronic functional field. The previous reports focused mainly on mononuclear Ru(II) complexes, and there had been little research on the comparison between mononuclear and binuclear Ru(II) complexes. In this work, a series of diamine ligands with bidentate and multiple dentate chelating sites were synthesized. Their Ru(II) complexes were synthesized and discussed in detail so that a direct comparison between mononuclear and binuclear Ru(II) complexes could be performed, including single crystals and electronic structure. To eliminate the effect of inhomogeneous microenvironment on sensing performance, these Ru(II) complexes were doped into a polymer matrix via electronspinning method. The sensing performance of mononuclear Ru(II) complexes was compared with that of binuclear Ru(II) complexes. It was concluded that binuclear Ru(II) complexes were superior to mononuclear Ru(II) complexes in sensitivity, response/sensitive performance and photostability. This was because there was more MLCT (metal-to-ligand-charge-transfer) contribution in a binuclear Ru(II) complex which was more O2 quenchable than LLCT (ligand-to-ligand-charge-transfer). There were two emissive/sensitive centers in a binuclear Ru(II) complex, offering more collision chances with O2 molecules and leading to fast response and recovery behavior, as well as improved photostability. The major advantage of this work was the observation of linear sensing response, which was rather rare for Ru(II)-based probes.