Naphthalene Benzimidazole Based Neutral Ir(III) Emitters for Deep Red Organic Light-Emitting Diodes

Abstract

Rigid naphthalene benzimidazole (NBI) based ligands (L1 and L2) are synthesized and utilized to make deep red phosphorescent cyclometalated iridium­(III) complexes ([Ir­(NBI)2(PyPzCF3)] (1) and [Ir­(DPANBI)2­(PyPzCF3)] (2)). Complexes 1 and 2 are prepared from the reaction of L1/L2 with the aid of ancillary ligands (PyPzCF3 , 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)­pyridine) in a two step method. The complexes are characterized by analytical and spectroscopic methods, as well as X-ray diffraction for 1. These complexes show a strong emission in the range of 635–700 nm that extends up to the near-infrared region (800 nm). The introduction of the diphenylamino (DPA) donor group on the naphthalene unit leads to a further red-shift in the emission. The complexes exhibit radiative quantum efficiency (ΦPL) of 0.27–0.29 in poly­(methylmethacrylate) film and relatively short phosphorescence decay lifetimes (τ = 1.1–3.5 μs). The structural, electronic, and optical properties are investigated with the support of density functional theory (DFT) and time-dependent-DFT calculations. The calculation results indicate that the lowest-lying triplet (T1) excited state of 1 has a mixed metal-to-ligand charge transfer (3MLCT) and ligand-centered (3LC) character, while 2 shows a dominant 3LC character. Deep red-emitting organic light-emitting diodes fabricated using 1 as a dopant display a maximum external quantum efficiency of 10.9% with the CIE color coordinates of (0.690, 0.294), with an emission centered at 644 and 700 nm. Similarly, the emitter 2 also shows a maximum external quantum efficiency of 6.9% with emissions at 657 and 722 nm.

Enhancement of Reverse Intersystem Crossing in Charge‐Transfer Molecule through Internal Heavy Atom Effect

“…Unlike the Ir-based phosphorescent materials with a fast k ISC of around 10 11 -10 12 s −1 , singlet excitons in fluorescent and TADF materials cannot be rapidly consumed via ISC. [3,33] As an exemplary model, Figure 5c clearly supports that N S at a pristine 4CzIPN model (@ k ISC ≈ 4.8 × 10 7 s −1 ) reduces by nearly two orders of magnitude within a few nano-seconds (@ k ISC ≈ 4.8 × 10 9 s −1 ) after a short electrical excitation (ceteris paribus). Interestingly, even only an ISC change brings out drastic changes in the amounts of N S at 10 −9 s (triangle symbol) while also reaching the time to a quasi-equilibrium state (circle symbol), in line with steady-state results.…”

Luminescent cyclometalated alkynylplatinum(ii) complexes with 1,3-di(pyrimidin-2-yl)benzene ligands: synthesis, electrochemistry, photophysics and computational studies

“…[8][9][10][11] The main advantage of employing organometallic complexes as emitters for the fabrication of highly efficient phosphorescent OLEDs is their capacity to access triplet states via intersystem crossing (ISC) from the singlet excited state through strong spin-orbit coupling mediated by the heavy metal in the complexes. [12][13][14][15][16][17] Phosphorescent transition metal compounds, such as iridium(III), 18 platinum(II), 19,20 ruthenium(II), 21 osmium(II) 22 and gold(III) complexes 23 have proven to be an outstanding class of emitter materials for making OLEDs because of their high luminescence quantum yields. The photophysical properties of luminescent metal complexes could be directly modulated by an appropriate variation of ligands and metal ions.…”

Heteroleptic Ir(III)-based near-infrared organic light-emitting diodes with high radiance capacity

“…S20 ) emerges at low doping concentrations. The higher the concentration, the easier it is for energy to transfer from the host to the dopant, thus the peak in the visible light area decreases 47 (see Fig. 5 b, Fig.…”