Europium complexes with large conjugation plane in diamine ligands: Synthesis, characterization, photophysical features and oxygen sensing performance

• Two ligands with large coplanar planes and proper triplet levels were designed.
• They europium complexes were prepared and characterized in detail.
• They were doped into a polymer matrix to construct composites for O2 sensing.
• Maximum sensitivity of 3.38 and short response time of 12 s were obtained.

In this paper, two europium complexes with large conjugation planes and proper triplet levels in their diamine ligands, Eu(DBM)3IPD and Eu3(DBM)9TBB, were synthesized and explored for oxygen sensing purpose, where DBM = 1,3-diphenyl-propane-1,3-dione, IPD = 4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-N,N-diphenylaniline, TBB = 1,3,5-tris((2-(pyridin-2-yl)-1H-benzo[d]imidazol-1-yl)methyl)benzene. It was anticipated that large conjugation planes and proper triplet levels could improve oxygen sensing performance by increasing collision probability with O2 molecules. The two europium complexes were firstly characterized through single crystal analysis, UV–Vis absorption spectra, emission spectra and excited state lifetimes. Then, by doping them into a polymer matrix of poly(vinylpyrrolidone) with electrospinning technique, oxygen sensing parameters of the resulting composite fibers were studied and compared. Maximum sensitivity of 3.38 and short response time of 12 s were obtained. Linear Stern–Volmer plots were observed.

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