Synthesis of a europium complex with ultrahigh quantum yield and its application as an invisible luminescent additive in pigments for preservation of cultural relics

Abstract

A europium coordination compound [Eu2(ppip)2(PhCOO)6] (ppip is 1,2-diphenylimidazo[4,5-f][1,10]phenanthroline) has been synthesized and structurally characterized. In this symmetric dinuclear complex of octa-coordinated Eu(III) atom, both hanging phenyl rings in the ppip are twisted dramatically from the imidazophenanthroline part, leading to strong edge-to-face (T-type) C–H∙∙∙π interaction. This pale yellow stable complex possesses an ultrahigh luminescence quantum yield (84.2 ± 0.2%) under excitation at 365 nm, and hence is explored to be utilized in the preservation pigments for traditional Chinese paintings as an luminescent additive, which looks invisible under normal light, but exhibits bright red luminescence under UV excitation at a rather low percentage (0.02% wt).