Abstract
We demonstrate a turn-on strategy for blue-emitting [Ir(C^N)2(P^P)]PF6 complexes and apply them to EL devices.
Highlights
Iridium complexes have attracted much attention due to their relatively short-lived triplet excited states and high photoluminescence quantum yields (ΦPL), which are crucial properties for emitters employed in organic light emitting diodes (OLEDs) or lightemitting electrochemical cells (LEECs)
The purity of the complexes was confirmed by 1H, 13C, 19F and 31P NMR spectroscopy, HRMS and melting point analyses (1H, 13C, 31P, 19F-NMR and HRMS spectra are reported in the Electronic supplementary information (ESI)†)
Through optimization of the bite angle of the P^P chelate and introduction of bulky and fluorinated C^N ligands, we have rationally designed the brightest reported blue-emitting complex of this class in 4c (ΦPL: 52%). These complexes exhibit irreversible electrochemistry, which perhaps accounts for the poor LEEC performances observed using complexes 1b, 4a, 4b and 4c
Summary
The expansion of low-cost and more efficient lighting sources based on phosphorescent materials is one of the greatest challenges of our century.1 In particular, iridium complexes have attracted much attention due to their relatively short-lived triplet excited states (τe) and high photoluminescence quantum yields (ΦPL), which are crucial properties for emitters employed in organic light emitting diodes (OLEDs) or lightemitting electrochemical cells (LEECs).2 In addition, due to Recently, examples of sky-blue and deep-blue emitting cationic iridium complexes bearing biimidazole,6 bis(NHC),7 substituted triazole or tetrazole,8 or pyrazolyl-pyridine9 as ancillary ligands have been explored, but challenges still remain regarding efficiencies and stabilities of these emitters in devices.10there is still a demand for blue-emitting phosphors as emitters in lighting devices.The vast majority of cationic iridium complexes possess the motif [Ir(C^N)2(N^N)]+, where C^N is a cyclometalating ligand with 2-phenylpyridinato ( ppy) as the archetype and N^N is an ancillary ligand with 2,2′-bipyridine (bpy) as the archetype.11Despite their prominence as ligands in homogeneous catalysis,12 phosphorus(III)-based ligands have remained underexplored in their complexation to iridium(III). Considering the improved photophysical properties observed for 3c, we decided to evaluate the family of dFmesppy cyclometalated complexes bearing xantphos, dpephos and dppe as ancillary ligands, with a view to reducing the intramolecular interactions and the quenching phenomena following introduction of the bulky mesityl substituent.22 Disappointingly, the observed ΦPL and τe values for 4a and 4b remained essentially unaltered compared to analogs 2a and 2b.
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