Molecular Engineering of Iridium Blue Emitters Using Aryl N‐Heterocyclic Carbene Ligands

Abstract

The synthesis of a new series of neutral bis[2‐(2′,4′‐difluorophen‐2′‐yl)pyridine][1‐(2′‐aryl)‐3‐methylimidazol‐2‐ylidene]iridium(III) complexes is reported. Each complex has been characterized by NMR spectroscopy, UV/Vis spectrophotometry, and cyclic voltammetry, and the photophysical properties examined in depth. Furthermore, two of the complexes have been characterized by single‐crystal X‐ray diffraction analysis. By systematically modifying the cyclometalating aryl group on the N‐heterocyclic carbene (NHC) ligand from 2,4‐dimethoxyphenyl to 6‐methoxy‐2‐methyl‐3‐pyridyl, the energy levels of the Ir complexes were modified to produce new blue emitters with increased HOMO and triplet‐state energies. OLED devices fabricated with these emitters showed external quantum efficiencies (EQEs) in the range of 2.3–3.2 % with low turn‐on values of 2.7–2.9 V and efficacies of up to 6.3 %.

Exploration of Bis(Arylimidazole) Iridium Picolinate Complexes

“…The PLQY measurements were performed relative to FIrPic in DCE (PLQY = 92%), as described previously. 25,26 As has been described for a serious of recently published heteroleptic phenylpyridine acetylene-substituted picolinates, the observed PLQY values were much lower than those for FIrPic, but similar to those for Ir(ppy)2(pic) (14.7%). 23 Complex 12 exhibited the highest PLQY (24.7%) and complex 13 the lowest (6.4%).…”

“…Our first set of measurements involved obtaining excited state lifetime and photoluminescence quantum yield (PLQY, Φ) data for the complexes (Table2). The PLQY measurements were performed relative to FIrPic in DCE (PLQY = 92%), as described previously 25,26. As has been described for a serious of recently published heteroleptic phenylpyridine acetylene-substituted picolinates, the observed PLQY values were much lower than those for FIrPic, but similar to those for Ir(ppy)2(pic) (14.7%) 23.…”

Luminescent Platinum(IV) Complexes Bearing Cyclometalated 1,2,3‐Triazolylidene and Bi‐ or Terdentate 2,6‐Diarylpyridine Ligands

“…We anticipated that the donor properties of the triazolylidene moiety would benefit the emission efficiencies of cyclometalated Pt IV complexes by increasing the energy of deactivating excited states of LMCT character to a greater extent than in the case of 2‐arylpyridines. Cyclometalating aryl‐NHC ligands have previously been employed for the synthesis of luminescent complexes of Ir III , Pt II , and Au III[57] with enhanced emission properties, often as non‐chromophoric supporting ligands. However, most of them are normal 2‐imidazolylidene‐type aryl‐NHCs, whereas mesoionic aryl‐NHCs have only been employed to prepare a limited number of luminescent Pt II complexes of the type [Pt(C^C*)(O^O)] (O^O=β‐diketonate) .…”

Synthesis, Spectroscopic, and Photophysical Studies of Phosphorescent Bis(2-(2,4-difluorophenyl)pyridine)Iridium(III) Complex Containing Derivative of 1<i>H</i>-1,2,4-Triazole Anchillary Ligand

“…Nazeeruddin et al reported the designation of three blue iridium(III) complexes having similar modification strategies, with the dfppy (difluorophenylpyridine) primary cyclometalating ligand and NHC of imidazolium salt as an anchillary ligand. The emission is considerably blue-shifted to 467 and 464 nm when modifying the pyridylimidazole using methoxy, dimethoxy, and methyl substituent but their photoluminescence quantum yields (PLQYs) calculation is still at an average of 0.310.66 [7]. In addition, earlier studies on utilizing methyl and phenyl substituent into the imidazole ring also improved iridium(III)-carbene complexes [2].…”

“…However, in general, the fluorescence color of iridium(III) complexes is easily affected by the alteration of the ligand bonded to the central metal [4][5]. Up to this point, the design of phosphorescent green and red emitter displays has been incredibly successful, whereas the development and innovation of highly efficient, long-lived blue emitters have remained a challenge [6][7]. Therefore, numerous strategies have been developed to modify the emission to blue, one of which is the employment of strong donating ligands such as triazole [8][9].…”