Metallophilic Interactions in Bimetallic Cyclometalated Platinum(II) N‐Heterocyclic Carbene Complexes

Abstract

Platinum(II) complexes with rigid and electron donating ligands are efficient phosphorescent emitters at room temperature. However, the excited‐state lifetimes of these complexes are, in general, relatively long. This problem, which can result in the degradation of the emitter, can be overcome by exploiting the natural tendency of platinum to form metallophilic interactions and aggregates. Herein, we report platinum(II) bimetallic complexes with 100 % quantum yield and at the same time exceptionally short radiative decay times, which in some cases are up to a hundredfold faster than the analogous monometallic complexes.

Exceedingly Stable Luminescent Dinuclear Pt(II) Complexes with Ditopic Formamidinate Bridging Ligands for High‐Performance Red and Deep‐Red OLEDs with LT97up to 2446 h at 1000 cd m−2

“…[15] This is consistent with the observation for related cyclometalated Pt(II) dimers that show an emissive 3 MMLCT [dσ*(Pt 2 )→π*(C^C*)] excited state. [11,12] A redshift in emission λ max of 3-12 nm was observed for 3(C), 4(C), 5, and 6 upon increasing solvent polarity (Figure S11…”

“…During the preparation of this manuscript, Strassner et al reported the synthesis and photophysical data of 5. [12] In principle, the ditopic bis-µ 2 -formamidinate bridging ligands could adopt multiple structural arrangements with respect to the two [Pt(C^C*)] units, such as forms A, B, and C depicted in Figure 1. In this work, only two of the geometric isomers of [Pt(C^C*)] 2 (N 4 ) (1-4) were obtained.…”

“…A less intense low-energy broad absorption band attributed to the [dσ*(Pt 2 )→π*(C^C*)] 1 MMLCT transition is observed at 472-526 nm (ε = 5.7-9.8 × 10 3 dm 3 mol −1 cm −1 ). [11,12] The 1 MMLCT absorption energy is inversely correlated to the π-accepting property of the heterocycle of cyclometalating ligands, being in the order of pzNHC < pyNHC, which is parallel to the trend of the reduction potentials of the complexes. As shown in Figure 3a, Figure S9a, Supporting Information, the UV-visible absorption profiles of the major isomers, 1(A), 2(A) and 3(C), resemble that of 5.…”

“…To date, only a few examples of red/deep red emitters based on discrete dinuclear Pt(II) complexes with high emission quantum yields (>0.6) have been reported. [10][11][12] Enlightened by Strassner's works, [11] the dinuclear Pt(II) complexes assembled by using cyclometalating [C^C*] and [N^N]/[N 4 ] formamidinate ligands could secure the efficient formation of 3 MMLCT excited states that are insensitive to the media and complex concentration. The k r values of these Pt(II) emitters are large in both solution and films, reaching up to 6 × 10 5 s −1 .…”

“…[5] "Half-lantern" dibridged cyclometalated Pt(II) complexes with short intramolecular Pt-Pt contacts of <3.0 Å provide alternative access to the low-energy emissive 3 MMLCT excited state. Although a wide variety of dinuclear cyclometalated Pt(II) emitters showing 3 MMLCT emissions have been reported, [6][7][8][9][10][11][12] the stable red to NIR OLEDs with high EQE values and prolonged operational lifetimes (LT 97 > 1000 h) at The utilization of triplet metal-metal-to-ligand-charge-transfer ( 3 MMLCT) emissions of Pt(II) complexes having a large radiative decay rate is a promising strategy to develop efficient red and deep-red emitters for practical organic light-emitting diodes (OLEDs). The panel of robust luminescent dinuclear Pt(II) emitters described here features pyridine-/pyrazine-fused N-heterocyclic carbene-based cyclometalating ligands and ditopic bis-µ 2formamidinate bridging ligands.…”