Highly Photoluminescent Blue Ionic Platinum-Based Emitters

Abstract

New cycloplatinated N-heterocyclic carbene (NHC) compounds with chelate diphosphines (P^P) as ancillary ligands: [Pt(R-C^C*)(P^P)]PF6 (R = H, P^P = dppm 1A, dppe 2A, dppbz 3A; R = CN, P^P = dppm 1B, dppe 2B, dppbz 3B) have been prepared from the corresponding starting material [{Pt(R-C^C*)(µ-Cl)}2] (R = H, A, R = CN, B) and fullycharacterized. The new compound A has been prepared by a stepwise protocol. The photophysical properties of 1A-3A and 1B-3B have been widely studied and supported by the time-dependent-density functional theory (TD-DFT). These compounds show an efficient blue (dppe, dppbz) or cyan (dppm) emission in PMMA films (5%wt), with photoluminescence quantum yield (PLQY) ranging from 30% to 87% under argon atmosphere. This emission has been assigned mainly to transitions from 3 ILCT [π(NHC) → 2 π*(NHC)] excited states with some 3 LL'CT [π(NHC) → π*(P^P)] character. The electroluminescence of these materials in proof-of-concept solution processed OLEDs containing 3A and 3B as dopants was investigated. The CIE coordinates for devices based on 3A (0.22, 0.41) and 3B (0.24, 0.44) fit within the sky blue region. raise the energy of the MC states hindering their photo-or thermal population and then increasing the emission quantum yield and avoiding degradation via bond-breaking processes. 20, 23 The use of didentate cyclometalated carbenes (C^C*) allows to tune the emission properties by changing the nature of both, the C^C* and the ancillary ligands. In this field high efficient blue-emitters have been reported by our group. [19][20][21][22] Those containing chelate diphosphines, such as [Pt (R-C^C*)(P^P)] PF6 (R-C= Naph, R =CO2Et, P^P: dppm (diphenylphosphinomethane), dppe (diphenylphosphinoethane), dppbz (1,2diphenylphosphino-benzene) showed high photoluminescence quantum yields (PLQY) and stability and were proved as the active components in photo-and electroluminescent devices. 21 OLEDs can be manufactured with either vacuum deposition or solution-processing techniques. The former method is suitable for small molecules that, generally, have better performance and longer stability due to the purity of the sublimated samples. [24][25][26] Vacuum deposition, however, requires accurate control on doping concentration and wastes lot of material thereby increasing the manufacturing costs. 27 Recent developments on solutionprocessable OLEDs based on small molecules have focused on optimizing efficiency while using simple processing techniques. 27 However, there are still limited examples, in particular for solution-processable OLEDs based on Pt(II) complexes. 25,26,[28][29][30][31][32][33][34][35][36][37][38][39][40] Within this perspective we decided to extend the family of [Pt(R-C^C*)(P^P)]PF6 compounds by changing the C^C* group. As result, herein we report the synthesis and the structural properties of compounds [Pt (R-C^C*)(P^P)]PF6 (R= H, P^P: dppm 1A, dppe 2A, dppbz 3A; R = CN, P^P: dppm 1B, dppe 2B, dppbz 3B). The photophysical and TD-DFT studies were also carried out, showing photoluminescence...

Cyclometalated NHCs Pt(II) Compounds with Chelating P^P and S^S Ligands: From Blue to White Luminescence

“…The X-ray study of 6A , 6B , and 7A (Figures , S56, and S57 and Table ) confirmed their molecular structures showing a really distorted square-planar coordination environment for the metal with C(1)–Pt–C(10) and X(1)–Pt–X(2) (X = P for 6A and 6B , S for 7A ) bite angles of 79°–73°. Regarding the “Pt­(C^C* A/B )” moiety, the Pt–C bond parameters are similar to those of reported platinacycles with N-heterocyclic carbenes, ,,,,− and the five-membered platinacycle and the Pt coordination plane result almost coplanar (Table ).…”

“…If we compare the powder QY of 5B (7%) and 6B (57%), with [Pt­(C^C* B )­(P^P)]­PF 6 (P^P = dppm, dppe, dppbz) [QY = 10–40%], having the same cyclometalated carbene (C^C* B ) but different P^P ligand, it can be observed the great influence of the chelating diphosphine. Also, compound 6B proved to be among or even better than the best blue Pt­(II) emitters whether in solid state or doped film. ,,− ,− Nonetheless, the CIE coordinates (0.17, 0.30) slightly deviate from the desired ones for deep blue emitters (0.15, 0.22), see Figure .…”

“…Given the great interest in stable and efficient luminescent compounds and our previous results of bright-blue emitters using cyclometalated NHC complexes of Pt­(II), − we decided to investigate new Pt­(C^C*) systems with different chelating ancillary ligands that present varied steric and electronic properties. Thus, we prepared a new NHC cycloplatinated compound [Pt­(C^C* A )­ClMeCN] (HC^C* A -κC* A = 1-(4-(ethoxycarbonyl)­phenyl)-3-methyl-1 H -benzimidazol-2-ylidene, 4A ) following our stepwise procedure.…”

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

“…To increase the stability of an OLED device, a phosphorescent emitter should be characterised by short radiative decay times, as long‐lived excited states enhance the possibility of side reactions that limit the lifetime of an OLED. Most of the * platinum(II) complexes exhibit radiative decay times in the order of 5–30 μs, [2a] but in some cases, extremely fast radiative decay times have been observed [3a,c,4f] . In bimetallic platinum(II) complexes where the Pt−Pt distances are shorter than the sum of the Van der Waals radii of the two platinum(II) atoms, strong metallophilic interactions influence the photophysical properties of these emitters and the excited‐state structure [6] .…”

Unusual [Pt{κ2(C,N)}]+ → [Pt{κ2(N,N)}]+ Coordination Mode Flip of the Guanidinate(1−) Ligand in Cationic N,N′,N″-Tris(3,5-xylyl)guanidinatoplatinum(II) Bis(phosphine) Complexes. Syntheses, Structural and Theoretical Studies

“…195 Pt NMR spectroscopy is a useful technique to probe the environment around the square-planar Pt­(II) complexes. ,,− δ­( 195 Pt) values of platinacycles prepared in the present investigation except for the shift of 20 were measured and are given in Table . 195 Pt NMR spectra of 10 – 15 revealed a doublet of doublets in the range δ­( 195 Pt) −3755 to −3917 ppm ( 1 J Pt–P = 3400–3448 and 1438–1499 Hz) due to coupling with two distinct P nuclei.…”