Highly photo- and electroluminescent 1,3-diketonate Eu(iii) complexes with spiro-fluorene-xantphos dioxide ligands: synthesis and properties

Abstract

Spiro-fluorene-xanthene-bis(diphenylphosphine) dioxide turned out to be a particularly effective co-sensitizer for Eu(hfa)₃, Eu(tta)₃ and Eu(nta)₃ photoluminescent complexes. These ternary complexes proved to be particularly good materials for pure red color OLED devices. Two complexes, Eu(tta)₃ and Eu(nta)₃, were selected for OLED device testing. Surprisingly, these complexes displayed excellent performance within known Eu(III) complexes, as OLED materials. The electroluminescence (EL) spectra of Eu(tta)₃SFXPO and Eu(nta)₃SFXPO OLEDs show only Eu emission with a peak at 612 nm. The CIE coordinates are (0.65,0.32) for Eu(tta)₃SFXPO OLEDs and (0.66,0.33) for Eu(nta)₃SFXPO OLEDs, which means that the emission from these Eu-based OLEDs is pure red. At a brightness of 100 Cd m⁻², Eu(tta)₃SFXPO OLEDs have an external quantum efficiency of 2.4%, a power efficiency of 0.6 lm W⁻¹ and a current efficiency of 3.2 Cd A⁻¹. To our knowledge, this external quantum efficiency value is more than the best that has been previously reported for solution-processed Eu-based OLEDs at a brightness of 100 Cd m⁻². More excitingly, Eu(nta)₃SFXPO OLEDs shows an even better performance. At a brightness of 100 Cd m⁻², Eu(nta)₃SFXPO OLED possesses an external quantum efficiency of 3.7%, a power efficiency of 1.0 lm W⁻¹ and a current efficiency of 5.1 Cd A⁻¹. These OLED devices for testing were manufactured by a solution-processing method.