Circularly Polarized Phosphorescent Electroluminescence from Chiral Cationic Iridium(III) Isocyanide Complexes

Abstract

applications in optical data storage, backlights in 3D displays and liquidcrystal display, spin sources in optical spintronics, and information carriers in quantum computation. [1][2][3][4][5][6][7][8][9][10] For CPL, the luminescence dissymmetry factor (g factor) is an important parameter to evaluate the degree of polarization, which is defined as g = ΔI/I = 2(I L − I R )/(I L + I R ), where I L and I R represent the left and right-handed luminescence polarized intensity values, respectively. [11,12] Currently, CP light is often obtained from nonpolarized light through the filters, which however results in low efficiency and high cost. So it is necessary to develop a new generation of device that can directly emit CP light. [13] Circularly polarized phosphorescent organic light-emitting diodes (CP-PhOLEDs) based on transition metal complexes, such as those of Ir(III) and Pt(II), are able to achieve theoretically 100% internal quantum efficiency through harvesting triplet excitons because singlet and triplet excitons can be synchronously utilized by spin-orbit coupling interactions induced by heavy metal atoms. [14][15][16][17][18] To the best of our knowledge, there are few reports about the utilization of chiral phosphorescent Pt(II) or Ir(III) complexes in CP-PhOLEDs. For example, Shen et al. designed a series of Pt(II) complexes (see A1 in Figure 1 and Table S1, Supporting Information) bonding a chiral sulfoxide ligand, which showed red emission and possessed a relatively high g value of the order of 10 −3 but without further capitalizing on the devices. [19] More recently, Brandt et al. synthesized a phosphorescent Pt(II) complex (see A2 in Figure 1 and Table S1, Supporting Information) with helical chirality achieving efficient red phosphorescence emission of devices but with inferior device performance, and its highest |g EL | value was up to 0.38. [20] However, it is difficult to tune the emission color of these Pt(II) complexes to the shorter wavelength. Owing to the advantageous photophysical properties of phosphorescent Ir(III) complexes, such as high luminescence quantum yields and tunable emission colors, they are the most excellent candidate for CP-PhOLEDs. [21][22][23][24] However, there are very few reports about the use of phosphorescent Ir(III) complexes as chiral emissive dopants in CP-PhOLEDs. For example, Li et al. reported a series of iridium phosphor isomers by introducing a chiral carbon center (R/S-edp, (R)/(S)-2-(4-ethyl-4,5-dihydrooxazol-2-yl) phenol) as ancillary ligands to obtain enantiomeric Ir(III) complexes (see B1 and B2 in Figure 1 and Table S1, Circularly polarized organic light-emitting diodes (CP-OLEDs), which directly emit CP light from organic light-emitting diodes, have attracted considerable attention because of their wide applications in various photonic devices. In this work, a pair of chiral bis-cyclometalated phosphorescent iridium(III) isocyanide complexes is designed and synthesized, which exhibits almost the same photophysical properties and obvious mirror image in ...

Configurationally Stable Platinahelicene Enantiomers for Efficient Circularly Polarized Phosphorescent Organic Light‐Emitting Diodes

“…In 2015, our group reported highly efficient circularly polarized phosphorescent OLEDs (CP‐PhOLEDs) with | g EL | of 2.6×10 −3 by introducing chiral iridium(III) complexes as the emitters . Later, Zhao's group also reported CP‐PhOLEDs based on chiral Ir III isocyanide complexes achieving the | g EL | of 3 × 10 −3 , which is the highest value among the reported CP‐PhOLEDs based on Ir III complexes …”

“…[13] Later, Zhao's group also reported CP-PhOLEDs based on chiral Ir III isocyanidec omplexes achieving the j g EL j of 3 10 À3 ,w hichi st he highest valuea mong the reported CP-PhOLEDs based on Ir III complexes. [14] Among the chiral units, helicene derivatives are at ype of polycyclic compounds with non-planar skeleton forming a spirals tructure whiche ndowst hem with the characteristic of chirality. [15] These unique features make helicene an effective chirals ource for constructing chiral materialss uch as polymers and metallahelicenes.…”

Recent Progress on Circularly Polarized Luminescent Materials for Organic Optoelectronic Devices

“…For example, a series of ionic complexes 36 – 40 were designed and synthesized. For the circularly polarized phosphorescent signals, all of them showed small g lum factors in the scope of 10 −3 . The phosphorescent CP‐OLEDs were fabricated using R/S isomers ( 36 ), and the performance of the devices for R / S‐doped in PVK:OXD‐7 (7:3, w/w) host materials including the maximum luminance, power, and current efficiencies were in the range of 3507–4473 cd m −2 , 1.94–2.55 lm W −1 , and 4.90–7.50 cd A −1 , respectively.…”

Computational simulation of vibrationally resolved spectra for spin‐forbidden transitions

“…Phosphorescent materials, particularly those containing transition metal complexes, have found application in several fields and have been the object of extensive studies in recent years, thanks in part to their applicability in electroluminescent devices such as organic light‐emitting diodes, sensors, and probes . In particular, chiral emitting systems are especially appealing because of their possible application in data storage, directional backlight 3D displays, and liquid crystal displays, as spin sources in optical spintronics and information carriers in quantum computing . Phosphorescence spectroscopy is the method of choice for the study of phosphorescent materials; however, the characterization of chiral systems would require a chiral spectroscopy, an example of which is circularly polarized luminescence, probing the differential emission of left and right circularly polarized light.…”

“…[1][2][3][4] In particular, chiral emitting systems are especially appealing because of their possible application in data storage, directional backlight 3D displays, and liquid crystal displays, as spin sources in optical spintronics and information carriers in quantum computing. [5][6][7][8][9][10][11][12] Phosphorescence spectroscopy is the method of choice for the study of phosphorescent materials; however, the characterization of chiral systems would require a chiral spectroscopy, an example of which is circularly polarized luminescence, probing the differential emission of left and right circularly polarized light. When associated to triplet-singlet transitions, this technique is also known as circularly polarized phosphorescence (CPP).…”