A unique white electroluminescent one-dimensional europium(iii) coordination polymer

Abstract

Optoelectronic lanthanide coordination polymer is a formidable challenge, because of its labile structure during device fabrication and incident emission quenching. In this work, an efficient electroluminescent (EL) one-dimensional Eu³⁺ coordination polymer, named Eu-FDPO, is first achieved with structural feature of bidentate phosphine oxide ligand FDPO bridged Eu(DBM)₃ complex units (DBM is dibenzoylmethane). X-ray diffraction analysis verified preserved one-dimensional-chain structure of spin-coated Eu-FDPO film on the basis of stable and flexible coordination between FDPO and Eu³⁺ ion, making its device fabrication feasible. Wolf-III type configuration endows Eu-FDPO with unique and preeminent physical properties, especially high photoluminescent quantum yield over 80% in film, suitable frontier molecular orbital energy levels for effective charge injection and peculiar intra-chain carrier transportation with high electron mobility close to 10⁻⁶ cm² V⁻¹ s⁻¹, indicating the predominance of Wolf-III type lanthanide coordination polymers in optoelectronic applications to their Wolf-I and II type counterparts. It is shown that FDPO is crucial as an intermediate in optoelectronic processes to establish channels for efficient intra-chain energy and charge transfer. Consequently, double-layer spin-coated devices of Eu-FDPO realized the best EL performance among Eu³⁺ coordination polymers to date, including low driving voltage of 10.2 V at 100 cd m⁻² and high luminance and efficiency with maxima of 215 cd m⁻² and 0.71 cd A⁻¹, respectively, as well as unique single-polymer white EL emission with favorable color coordinates of (0.38, 0.32).