Dual-Phosphorescent Heteroleptic Silver(Ⅰ) Complex in Long-Lasting Red Light-Emitting Electrochemical Cells

摘要

The design of red-emitting silver(Ⅰ) complexes and their implementation inthin-film lighting are still challenging as (ⅰ) their high ligand-field splittingenergy leads to high-energy emissions with a controversial mechanism(thermally activated delayed fluorescence vs fluorescence/phosphorescence),and (ⅱ) their low electrochemical stability leads to the formation of silvernanoclusters, limiting device stability to a few seconds. Herein, a thoughtfulcomplex design Ag(xantphos)(deebq)PF6 combining a large-bite anglediphosphine ligand (xantphos), a rigid, sterically hindered, -extendedbiquinolin (deebq) is reported. In contrast to prior-art, this complex possesses(ⅰ) efficient red-emission ( _(em) = 660 nm; photoluminescence quantum yield of42) assigned to a thermally equilibrated dual-phosphorescent emissionbased on spectroscopic/theoretical studies and (ⅱ) stable reduction behaviorwithout forming silver nanoclusters. This results in the first red light-emittingelectrochemical cells featuring (ⅰ) improved stability of two orders ofmagnitude compared to prior-art (from seconds to hours) at irradiances of20 μW cm~（?2）, and (ⅱ) a new degradation mechanism exclusively related top-doping as confirmed by electrochemical impedance spectroscopy analysis.Indeed, a multi-layered architecture to decouple hole injection/transport andexciton formation enables a further 2-fold enhanced irradiance/stability.Overall, this work illustrates that deciphering the rules for silver(Ⅰ) complexdesign for lighting is tricky, but worthwhile.