A New Class of Sky-Blue-Emitting Ir(III) Phosphors Assembled Using Fluorine-Free Pyridyl Pyrimidine Cyclometalates: Application toward High-Performance Sky-Blue- and White-Emitting OLEDs

Abstract

Two pyrimidine chelates with the pyridin-2-yl group residing at either the 5- or 4-positions are synthesized. These chelates are then utilized in synthesizing of a new class of heteroleptic Ir(III) metal complexes, namely [Ir(b5ppm)2(fppz)] (1), [Ir(b5bpm)2(fppz)] (2), [Ir(b4bpm)2(fppz)] (3), and [Ir(b5bpm)(fppz)2] (4), for which the abbreviations b5ppm, b5bpm, b4bpm, and fppz represent chelates derived from 2-t-butyl-5-(pyridin-2-yl)pyrimidine, 2-t-butyl-5-(4-t-butylpyridin-2-yl)pyrimidine, 2-t-butyl-4-(4-t-butylpyridin-2-yl)pyrimidine, and 3-trifluoromethyl-5-(pyridin-2-yl) pyrazole, respectively. The single crystal X-ray structural analyses were executed on 1 to reveal their coordination arrangement around the Ir(III) metal element. The 5-substituted pyrimidine complexes 1, 2, and 4 exhibited the first emission peak wavelength (λmax) located in the range 452-457 nm with high quantum yields, whereas the emission of 3 with 4-substituted pyrimidine was red-shifted substantially to longer wavelength with λmax = 535 nm. These photophysical properties were discussed under the basis of computational approaches, particularly the relationship between emission color and the relative position of nitrogen atoms of pyrimidine fragment. For application, organic light-emitting diodes (OLEDs) were also fabricated using 2 and 4 as dopants, attaining the peak external quantum, luminance, and power efficiencies of 17.9% (38.0 cd/A and 35.8 lm/W) and 15.8% (30.6 cd/A and 24.8 lm/W), respectively. Combining sky blue-emitting 2 and red-emitting [Os(bpftz)2(PPh2Me)2] (5), the phosphorescent white OLEDs were demonstrated with stable pure-white emission at CIE coordinate of (0.33, 0.34), and peak luminance efficiency of 35.3 cd/A, power efficiency of 30.4 lm/W, and external quantum efficiency up to 17.3%.

Solution-Processed Blue/Deep Blue and White Phosphorescent Organic Light-Emitting Diodes (PhOLEDs) Hosted by a Polysiloxane Derivative with Pendant mCP (1,3-bis(9-carbazolyl)benzene)

“…[32][33][34][35] The small-molecule mCP [1,3-bis(9-carbazolyl)benzene] which has a triplet energy of 2.9 eV is widely used in this context. [36][37][38][39][40][41] However, mCP tends to crystallize as a consequence of its rather low T g (glass transition temperature, 60 °C). It is a challenge to develop a polymeric host that has a higher T g than mCP while maintaining mCP's desirable optoelectronic properties.…”

Finely Tuned Blue Iridium Complexes with Varying Horizontal Emission Dipole Ratios and Quantum Yields for Phosphorescent Organic Light‐Emitting Diodes

“…Whereas, purity is slightly reduced for tBu‐FCNIr probably due to the decomposition of the material coming from the high sublimation temperature of 445 °C which is about 100 °C higher than the heteroleptic complexes. This phenomenon is commonly observed in fluorinated blue complexes due to the volatile nature of fluorine at high temperatures . The complex tBu‐FCNIr was obtained in two isomeric forms with fac isomer as the major product over 98% and mer isomer less than 2% (Figure S5 in SI).…”

11,16‐Di‐tert‐butyl‐9,18‐diphenylbenzo[kl]benzo[8,9]triphenyleno [2,3‐b]xanthene: Synthesis, Photophysics, Self‐Assembly and Electroluminescent Properties

“…The optimal device BTX exhibited green emission with Commission International de l'Eclairage (CIE) coordinate of (0.14, 0.53) at the brightness of 1000 cd m −2 . The electroluminescent band of device BTX was at 486/518 nm (Figure S9), being slightly red‐shift compared with those in dichloromethane solution (475/508 nm), but being close to those in thin film (481/512 nm, Figure S10), suggesting that the as‐formed excitons were heavily confined in the emitting layer . By the way, there was a negligible variation with the increase of driving voltages, inferring good electroluminescent color stability.…”