White Light Emission from Planar Remote Phosphor Based on NHC Cycloplatinated Complexes

Abstract

We report on the generation of bright white luminescence through solid-state illumination of remote phosphors based on novel cycloplatinated N-heterocyclic carbene (NHC) compounds. Following a stepwise protocol we got the new NHC compound [{Pt(μ-Cl)(C(∧)C*)}2] (4) (HC(∧)C*-κC* = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene), which was used together with the related ones 4a (HC(∧)C*-κC*= 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene) and 4b (HC(∧)C*-κC*= 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene) as starting materials for the synthesis of the new ionic derivatives [Pt(R-C(∧)C*) (CNR')2]PF6 (R = -COOEt, R' = t-Bu (5), Xyl (6); R = -CN, R' = t-Bu (7), Xyl (8); R(∧)C = Naph, R' = t-Bu (9), Xyl (10)). The X-ray structures of 6 and 8-10 have been determined. The photophysical properties of these cationic compounds have been studied and supported by the time-dependent-density functional theory (TD-DFT) calculations. The compounds 5, 8, and 9 have been revealed as the most efficient emitters in the solid state with quantum yields of 41%, 21%, and 40%, respectively. White-light remote-phosphors have been prepared just by stacking different combinations of these compounds and [Pt(bzq) (CN) (CN(t)Bu)] (R1) as blue (5, 8), yellow (9), and red (R1) components onto the same substrate. The CCT (correlated color temperature) and the CRI (color rendering index) of the emitted white-light have been tuned by accurately controlling the individual contributions.

The Use of Cyclometalated NHCs and Pyrazoles for the Development of Fully Efficient Blue PtII Emitters and Pt/Ag Clusters

“…The small bite angle of the cyclometalated ligand [80.17(10)°] together with the Pt−C6 and Pt−C1(C*) distances are similar to those found in other five‐membered metalocycles of Pt II with NHC ligands ,. These distances evidence the low trans influence of the 3,5‐Me 2 pzH ligands since them are shorter than those observed in complexes such as [Pt(NC‐C^C*)(P P)]PF 6 (P^P=diphenylphosphino‐ethane) and [Pt(R‐C^C*)(C≡NR′) 2 ]PF 6 (R=CN, CO 2 Et; R′=Xyl, t Bu) . The Pt−N bond distances are rather long and similar to those found in complex cis ‐[Pt(C≡C) 2 (Hdmpz) 2 ], which is in agreement with the high trans influence of both C atoms (C1 and C6) of the EtO 2 C‐C^C*‐κC,C* ligand, mainly the σ‐bonded C Ar (C6).…”

“…1450 cm −1 ] corresponding to the C=C/C=N stretches of the cyclometalated NHC ligands (see Figure for 1 b Figure S29 and Table ) with long emission lifetime decays (14–22 μs), typical of phosphorescent Pt II systems. The emission energies are neither affected by the nature of the RpzH ligand nor the anion and are very similar to those of related compounds containing the same “(C^C*)Pt” fragment ,…”

“…As a result, we got the new mononuclear bis‐pyrazole complexes [Pt(C^C*)(RpzH) 2 ]X, containing a cyclometalated NHC ligand (HC^C*=1‐(4‐(ethoxycarbonyl)phenyl)‐3‐methyl‐1 H ‐imidazol‐2‐ylidene). They were isolated as chloride (Cl − ), perchlorate (ClO 4 − ) or hexafluorophosphate (PF 6 − ) salts, which were possible because of the availability of [{Pt(C^C*)(μ‐Cl)} 2 ]( A ) as a starting material. Here, we describe their synthesis, characterization, and photophysical properties, explained in some cases with the aid of theoretical calculations (TD and DFT).…”

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

“…The group of Sicilia has recently applied some cyclometallated platinum(II) complexes bearing NHC ligands to develop WOLEDs, whose chemical structure is sketched in Fig. 9 [41]. Depending on the π-conjugation of the NHC-based bidentate ligand, emitting complexes with luminescence varying from blue ( 19 and 20 ) to yellow ( 21 ) were obtained.…”

“…Molecular structure of carbene-containing cyclometallated alkynylplatinum(II) complexes 19 – 21 [41]. …”