Junyou Pan

Efficient near-UV emitters based on cationic bis-pincer iridium(III) carbene complexes.

We report on the photophysical studies of two cationic near-UV emitters based on bis-pincer Ir(III) carbene complexes: [Ir(nBu)(C(NHC)(Me)CC(NHC))2]X, where Ir(nBu)(C(NHC)(Me)CC(NHC)) is (4,6-dimethyl-1,3-phenylene-κC(2))bis(1-butylimidazol-2-ylidene) and X = I(-) or PF6(-)). The compounds are highly emitting in deaerated CH3CN solution with emission maxima at 384 and 406 nm, and photoluminescence quantum yields of 0.41 and 0.38, for [Ir(nBu)(C(NHC)(Me)CC(NHC))2]I and Ir(nBu)(C(NHC)(Me)CC(NHC))2]PF6, respectively. In order to gain deeper understandings into their structural and electronic features, as well as to ascertain the nature of the excited states involved into the electronic absorption processes, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been performed on the ground and excited states of the closely related complex [Ir(Me)(C(NHC)(Me)CC(NHC))2](+). In the solid state, an emission at low energy is observed (λ(max) = 500 nm) for both complexes. However, the intensity of the emission at high energy versus the intensity of the new emission at low energy is dependent on the nature of counterions. The origin of this emission is not completely clear, but the experimental data point to the formation of trapping sites induced by aggregation processes involving the interaction between the cationic emitter and the counterion.

White Light from a Single-Emitter Light-Emitting Electrochemical Cell

We report a novel and generic approach for attaining white light from a single-emitter light-emitting electrochemical cell (LEC). With an active-layer comprising a multifluorophoric conjugated copolymer (MCP) and an electrolyte designed to inhibit MCP energy-transfer interactions during LEC operation, we are able to demonstrate LECs that emit broad-band white light with a color rendering index of 82, a correlated-color temperature of 4000 K, and a current conversion efficacy of 3.8 cd/A. It is notable that this single-emitter LEC configuration eliminates color-drift problems stemming from phase separation, which are commonly observed in conventional blended multiemitter devices. Moreover, the key role of the electrolyte in limiting undesired energy-transfer reactions is highlighted by the observation that an electrolyte-free organic light-emitting diode comprising the same MCP emits red light.

White Light-Emitting Electrochemical Cell

We report a light-emitting electrochemical cell (LEC) with air-stable electrodes and a solution-processed single-layer active material that emits warm-white light (CIE coordinates = (0.39, 0.43); color rendering index =83) with significant brightness (B) at a low voltage. The carefully tuned trichromatic device exhibits a short turn-on time (∼5 s to B > 100 cd/m(2)), high efficiency (3.1 cd/A at B = 240 cd/m(2)) and good operational stability (17 h at B > 100 cd/m(2)). We also report a blue LEC with a highly respectable set of device properties in the form of a turn-on time of ∼5 s, an efficiency of 3.6 lm/W and 5.6 cd/A, and an uninterrupted operational lifetime of 25 h. Finally, by analyzing data from trichromatic and monochromatic devices as well as from the constituent fluorescent CPs, we are able to point out a viable path toward further improvements in the performance of the white-emitting LEC.