A series of new emissive group 11 transition metal d(10)-complexes 1-8 bearing functionalized 2-pyridyl pyrrolide together with phosphine ancillary such as bis[2-(diphenylphosphino)phenyl] ether (POP) or PPh(3) are reported. The titled complexes are categorized into three classes, i.e. Cu(I) complexes (1-3), Ag(I) complexes (4 and 5), and Au(I) metal complexes (6-8). Via combination of experimental and theoretical approaches, the group 11 d(10)-metal ions versus their structural variation, stability, and corresponding photophysical properties have been investigated in a systematic and comprehensive manner. The results conclude that, along the same family, how much a metal d-orbital is involved in the electronic transition plays a more important role than how heavy the metal atom is, i.e. the atomic number, in enhancing the spin-orbit coupling. The metal ions with and without involvement of a d orbital in the lowest lying electronic transition are thus classified into internal and external heavy atoms, respectively. Cu(I) complexes 1-3 show an appreciable metal d contribution (i.e., MLCT) in the lowest lying transition, so that Cu(I) acts as an internal heavy atom. Despite its smallest atomic number among group 11 elements, Cu(I) complexes 1-3 exhibit a substantially larger rate of intersystem crossing (ISC) and phosphorescence radiative decay rate constant (k(r)(p)) than those of Ag(I) (4 and 5) and Au(I) (6-8) complexes possessing pure π → π* character in the lowest transition. Since Ag(I) and Au(I) act only as external heavy atoms in the titled complexes, the spin-orbit coupling is mainly governed by the atomic number, such that complexes associated with the heavier Au(I) (6-8) show faster ISC and larger k(r)(p) than the Ag(I) complexes (4 and 5). This trend of correlation should be universal and has been firmly supported by experimental data in combination with empirical derivation. Along this line, Cu(I) complex 1 exhibits intensive phosphorescence (Φ(p) = 0.35 in solid state) and has been successfully utilized for fabrication of OLEDs, attaining peak EL efficiencies of 6.6%, 20.0 cd/A, and 14.9 lm/W for the forward directions.

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Due to generally low conductivity and low carrier mobilities of organic materials, organic light-emitting devices ͑OLEDs͒ are typically optimized for light outcoupling by locating emitters around the first antinode of the metal electrode. In this letter, by utilizing device structures containing conductive doping, we investigate theoretically and experimentally the influences of the location of emitters relative to the metal electrode on OLED emission, and show that substantial enhancement in light outcoupling ͑1.2 times͒ or forward luminance ͑1.6 times͒ could be obtained by placing emitters around the second antinode instead of the first antinode. Depending on the detailed condition, the second-antinode device may also give more directed emission as often observed in strong-microcavity devices yet without suffering a color shift with viewing angles.

A new series of charge neutral Os(II) isoquinolyl triazolate complexes (1–4) with both trans and cis arrangement of phosphine donors are synthesized, and their structural, electrochemical and photophysical properties are established. In sharp contrast to the cis‐arranged complexes 2–4, the trans derivative 1, which shows a planar arrangement of chromophoric N‐substituted chelates, offers the most effective extended π‐delocalization and hence the lowest excited state energy gap. These complexes exhibit phosphorescence with peak wavelengths ranging from 692–805 nm in degassed CH2Cl2 at room temperature. Near‐infrared (NIR)‐emitting electroluminescent devices employing 6 wt % of 1 (or 4) doped in Alq3 host material are successfully fabricated. The devices incorporating 1 as NIR phosphor exhibit fairly intense emission with a peak wavelength at 814 nm. Forward radiant emittance reaches as high as 65.02 µW cm−2, and a peak EQE of ∼1.5% with devices employing Alq3, TPBi and/or TAZ as electron‐transporting/exciton‐blocking layers. Upon switching to phosphor 4, the electroluminescence blue shifts to 718 nm, while the maximum EQE and radiance increase to 2.7% and 93.26 (μW cm−2) respectively. Their performances are optimized upon using TAZ as the electron transporting and exciton‐blocking material. The OLEDs characterized represent the only NIR‐emitting devices fabricated using charge‐neutral and volatile Os(II) phosphors via thermal vacuum deposition.

We report the unprecedented dual properties of excited-state structural planarization and thermally activated delayed fluorescence (TADF) of 10-dimesitylboryl phenoxazine, i.e., PXZBM. Bearing a nonplanar phenoxazine moiety, PXZBM shows the lowest lying absorption onset at ∼390 nm in nonpolar solvents such as cyclohexane but reveals an anomalously large Stokes-shifted (∼14 500 cm) emission maximized at 595 nm. In sharp contrast, when a phenylene spacer is added between phenoxazine and dimesitylboryl moieties of PXZBM, the 10-(4-dimesitylborylphenyl)phenoxazine PXZPBM in cyclohexane reveals a much blue-shifted emission at 470 nm despite its red-shifted absorption maximized at 420 nm (cf. PXZBM). The emission of PXZBM further reveals solvent polarity dependence, being red-shifted from 595 nm in cyclohexane to 645 nm in CHCl. For rationalization, the steric hindrance between phenoxazine and the dimesitylboryl unit in PXZBM caused a puckered arrangement of phenoxazine at the ground state. Upon electronic excitation, as supported by the femtosecond early relaxation dynamics, spectral-temporal evolution and energetics calculated along the reaction potential energy surfaces, the diminution of N → B electron transfer reduces π-conjugation and elongates the N-B bond length, inducing the fast phenoxazine planarization with a time constant of 890 ± 100 fs. The associated charge-transfer reaction from phenoxazine (donor) to dimesitylboryl unit (acceptor) results in a further red-shifted emission in polar solvents. In stark contrast, PXZPBM shows a planar phenoxazine and undergoes excited-state charge transfer only. Despite the distinct difference in excited-state relaxation dynamics, both PXZBM and PXZPBM exhibit efficient TADF capable of producing highly efficient orange and green organic light emitting diodes with peak efficiencies of 10.9% (30.3 cd A and 18.7 lm W) and 22.6% (67.7 cd A and 50.0 lm W).

Tetradentate bis(pyridyl azolate) chelates are assembled by connecting two bidentate 3-trifluoromethyl-5-(2-pyridyl)azoles at the six position of pyridyl fragment with the tailored spiro-arranged fluorene and/or acridine functionalities. These new chelates were then utilized in synthesizing a series of Pt(II) metal complexes [Pt(Ln)], n = 1-5, from respective chelates L1-L5 and [PtCl2(DMSO)2] in 1,2-dimethoxyethane. The single-crystal X-ray structural analyses were executed on 1, 3, and 5 to reveal the generalized structures and packing arrangement in crystal lattices. Their photophysical properties were measured in both solution and solid state and are discussed in the context of computational analysis. These L1-L5 coordinated Pt(II) species exhibit intense emission, among which complex 5 shows remarkable solvatochromic phosphorescence due to the dominant intraligand charge transfer transition induced by the new bis(pyridyl azolate) chelates. Moreover, because of the higher-lying highest occupied molecular orbital of acridine, complex 5 can be considered as a novel bipolar phosphor. Successful fabrication of blue and white organic light-emitting diodes (OLEDs) using Pt(II) complexes 3 and 5 as the phosphorescent dopants are reported. In particular, blue OLEDs with 5 demonstrated peak efficiencies of 15.3% (36.3 cd/A, 38.0 lm/W), and CIE values of (0.190, 0.342) in a double-emitting layer structure. Furthermore, a red-emitting Os(II) complex and 5 were used to fabricate warm-white OLEDs to achieve peak external quantum efficiency, luminance efficiency, and power efficiency values as high as 12.7%, 22.5 cd/A, and 22.1 lm/W, respectively.

Recently bipolar phosphorescent host materials have attracted wide attention since they can achieve better charge balance and hence better device performance. In this work, we report the synthesis and physical properties of a novel bipolar host material containing the dimesityl borane/carbazole hybrid, CMesB. With a high triplet energy, CMesB is considered a promising universal host material and has been applied to phosphorescent OLEDs of various colors. Red/green/blue/white (RGBW) OLEDs based on CMesB all show high external quantum efficiencies (20.7% for red, 20.0% for green, 16.5% for blue, and 15.7% for white) at practical brightnesses. The results indicate that the bipolar host CMesB with high triplet energy has high potential in manufacturing RGBW OLEDs for display or lighting applications.