Blue-shifting the monomer and excimer phosphorescence of tridentate cyclometallated platinum(II) complexes for optimal white-light OLEDs

By using a tridentate N^C^N-coordinating ligand, the luminescence of a cyclometallated Pt(II) complex can be shifted into the blue region, without the problematic drop-off in quantum yield observed for bidentate analogues. The combination of blue-shifted monomer and excimer allows white-emitting OLEDs with high colour rendering index to be produced.     

Exceptionally fast radiative decay of a dinuclear platinum complex through thermally activated delayed fluorescence

A novel dinuclear platinum(ii) complex featuring a ditopic, bis-tetradentate ligand has been prepared. The ligand offers each metal ion a planar O^N^C^N coordination environment, with the two metal ions bound to the nitrogen atoms of a bridging pyrimidine unit. The complex is brightly luminescent in the red region of the spectrum with a photoluminescence quantum yield of 83% in deoxygenated methylcyclohexane solution at ambient temperature, and shows a remarkably short excited state lifetime of 2.1 μs. These properties are the result of an unusually high radiative rate constant of around 4 × 10⁵ s⁻¹, a value which is comparable to that of the very best performing Ir(iii) complexes. This unusual behaviour is the result of efficient thermally activated reverse intersystem crossing, promoted by a small singlet–triplet energy difference of only 69 ± 3 meV. The complex was incorporated into solution-processed OLEDs achieving EQE_max = 7.4%. We believe this to be the first fully evidenced report of a Pt(ii) complex showing thermally activated delayed fluorescence (TADF) at room temperature, and indeed of a Pt(ii)-based delayed fluorescence emitter to be incorporated into an OLED.

Efficient thermally activated delayed fluorescence (TADF) in a brightly luminescent diplatinum(ii) complex results in significant enhancement of the radiative decay rate.     

Synthesis,characterization and optical properties of a new cationic cyclometalated platinum(ii) complex

The cyclometalated platinum (II) complex, [Pt(ppy)(ppyH)₂] OTF, 2 , in which ppy and ppyH denote the cyclometalated and non‐cyclometalated 2‐phenylpyridine ligand respectively, was prepared from the reaction of the platinum(IV) complex [PtMe₃(OTF)], 1 , with 3 equiv 2‐phenylpyridine at room temperature. The cyclometalated complex 2 was characterized using ¹H NMR spectroscopy. The solid state structure of 2 was further identified by single crystal X‐ray structure determination. 2 displays a green emission in solution and in solid state at room temperature and TD‐DFT calculations is used to elucidate the origin of the electronic transitions in the UV–vis spectrum of 2 .     

Luminescent Cu(I) and Ag(I) coordination polymers: Fast phosphorescence or thermally activated delayed fluorescence

Three luminescent Cu (I) and Ag (I) coordination polymers based on donor-acceptor motif ligands are reported.Two Cu (I) coordination polymers both exhibit fast phosphorescence,which another Ag (I) coordination polymer present TADF photoluminescence emission at room temperature.     

Luminescent Cu(I) and Ag(I) coordination polymers: Fast phosphorescence or thermally activated delayed fluorescence

By applying two donor-acceptor motif molecules, 5,10-di(pyridin-4-yl)-5,10-dihydrophenazine (L1) and 10,10'-di(pyridin-3-yl)-10H,10'H-9,9'-spiroacridine (L2), as ligands and CuI/AgCF₃CO₂ as metal salt, we synthesized three coordination polymers, namely, {Cu₄(L1)₂I₄} (CP1), {Cu(L2)I·CHCl₃} (CP2) and {Ag(L2)CO₂CF₃·CHCl₃} (CP3). X-ray crystallographic analysis revealed that three coordination polymers all feature one-dimensional (1D) linear chains which are consisting of molecular boxlike units. In comparison with low photoluminescence quantum yield (PLQY) of two ligands, three coordination polymers, CP1, CP2 and CP3, present more intense photoluminescence with PLQY of 15%, 46% and 34% at room temperature respectively. The PL emission of CP1 and CP2 at room temperature could be attributed to the fast phosphorescence with lifetime both around 5 μs due to effective intersystem crossing (ISC). Whilst, it is worth noting that CP3 exhibit thermally activated delayed fluorescence (TADF) emission at room temperature.     

Synthesis and characterization of cyclometallated palladium(II) and platinum(II) complexes with amide-thiolate ligands

The redox reaction of bis(2-benzamidophenyl) disulfide (H₂L-LH₂) with [Pd(PPh₃)₄] in a 1:1 ratio gave mononuclear and dinuclear palladium(II) complexes with 2-benzamidobenzenethiolate (H₂L⁻), [Pd(H₂L-S)₂(PPh₃)₂] (1) and [Pd₂(H₂L-S)₂ (μ-H₂L-S)₂(PPh₃)₂] (2). A similar reaction with [Pt(PPh₃)₄] produced only the corresponding mononuclear platinum(II) complex, [Pt(H₂L-S)₂(PPh₃)₂] (3). Treatment of these complexes with KOH led to the formation of cyclometallated palladium(II) and platinum(II) complexes, [Pd(L-C,N,S)(PPh₃)]⁻ ([4]⁻) and [Pt(L-C,N,S) (PPh₃)]⁻ ([5]⁻). The molecular structures of 2, 3 and [4]⁻ were determined by X-ray crystallography.     

Aggregation-induced delayed fluorescence(AIDF) materials: a new break-through for nondoped OLEDs

正Nowadays,purely organic materials with delayed fluorescence(DF)are being enthusiastically developed and extensively utilized as light-emitting materials to fabricate OLEDs because of their high exciton utilization and metal-free nature.These DF materials usually have a small single-triplet splitting(ΔEST),and the nonradiative triplet excitons(75%)can be converted into radiative singlet excitons via thermally     

Synthesis, reactivity and crystal structures of platinum (II) and platinum (IV) cyclometallated compounds derived from 2- and 4-biphenylimines

The reaction of [Pt₂Me₄(μ-SMe₂)₂] with ligands 4-C₆H₅C₆H₄CHNCH₂CH₂NMe₂ (1a) and 2-C₆H₅C₆H₄CHNCH₂CH₂NMe₂ (1b) carried out in acetone at room temperature produced compounds [PtMe₂{4-C₆H₅C₆H₄CHNCH₂CH₂NMe₂}] (2a) and [PtMe₂{2-C₆H₅C₆H₄CHNCH₂CH₂NMe₂}] (2b), respectively, in which the imines act as bidentate [N,N′] ligands. Cyclometallated [C,N,N′] compounds [PtMe{4-C₆H₅C₆H₃CHNCH₂CH₂NMe₂}] (3a) and [PtMe{2-C₆H₅C₆H₃CHNCH₂CH₂NMe₂}] (3b), were obtained by refluxing toluene solutions of compounds 2a or 2b. Reaction of [Pt₂Me₄(μ-SMe₂)₂] with ligands 4-C₆H₅C₆H₄CHNCH₂Ph (1c) and 2-C₆H₅C₆H₄CHNCH₂Ph (1d) produced compounds [PtMe{4-C₆H₅C₆H₃CHNCH₂Ph}SMe₂] (5c) and [PtMe{2-C₆H₅C₆H₃CHNCH₂Ph}SMe₂] (5d) containing a [C,N] ligand, from which triphenylphosphine derivatives 6c and 6d were also prepared. In all cases, metallation took place to yield five-membered endo-metallacycles and formation of seven-membered or of exo-metallacycles was not observed. The reactions of 3a, 3b, 6c and 6d with methyl iodide were studied in acetone and gave the corresponding cyclometallated platinum (IV) compounds. All compounds were characterised by NMR spectroscopy and compounds 3b, 4a, 6c and 6d were also characterised crystallographically.     

Vapochromic and mechanochromic phosphorescence materials based on a platinum(II) complex with 4-trifluoromethylphenylacetylide

Planar platinum(II) complex Pt(Me(3)SiC≡CbpyC≡CSiMe(3))(C≡CC(6)H(4)CF(3)-4)(2) (6) with 5,5'-bis(trimethylsilylethynyl)-2,2'-bipyridine and 4-trifluoromethylphenylacetylide exhibits remarkable luminescence vapochromic and mechanochromic properties and a thermo-triggered luminescence change. Solid-state 6 is selectively sensitive to vapors of oxygen-containing volatile compounds such as tetrahydrofuran (THF), dioxane, and tetrahydropyrane (THP) with phosphorescence vapochromic response red shifts from 561 and 608 nm to 698 nm (THF), 689 nm (dioxane), and 715 nm (THP), respectively. Upon being mechanically ground, desolvated 6, 6·CH(2)Cl(2), and 6·(1)/(2)CH(2)ClCH(2)Cl exhibit significant mechanoluminescence red shifts from 561 and 608 nm to 730 nm, while vapochromic crystalline species 6·THF, 6·dioxane, or 6·THP affords a mechanoluminescence blue shift from 698 nm (THF), 689 nm (dioxane), or 715 nm (THP) to 645 nm, respectively. When the compounds are heated, a thermo-triggered luminescence change occurs, in which bright yellow luminescence at 561 and 608 nm turns to red luminescence at 667 nm with a drastic red shift. The multi-stimulus-responsive luminescence switches have been monitored by the changes in emission spectra and X-ray diffraction patterns. Both X-ray crystallographic and density functional theory studies suggest that the variation in the intermolecular Pt-Pt interaction is the key factor in inducing an intriguing luminescence switch.     

Existence of intramolecular triplet excimer of bis(9-fluorenyl)methane: phosphorescence and delayed fluorescence spectroscopic and ab initio studies

A concerted computational and experimental study has been undertaken to probe the conformational structure and excited-state dynamics of bis(9-fluorenyl)methane (BFM). We have observed that the relative intensity of the delayed excimer fluorescence of BFM is greatly enhanced in comparison with that of the normal fluorescence. This is presumably because the relative concentration of the triplet excimer is enhanced in comparison with the singlet excimer. B3LYP DFT/6-31G(d) calculations indicate that the sandwich conformer of BFM in the singlet ground state is unstable, whereas that in the triplet excited state has a bound state, being very slightly higher in internal and Gibbs free energies than that of the lowest state of the near-orthogonal conformer.     

Improved photostability and fluorescence properties through polyfluorination of a cyanine dye

[structure: see text] A polyfluorinated cyanine dye has been synthesized and characterized. Compared with the nonfluorinated analogue, the dye exhibits significantly reduced aggregation in aqueous media, enhanced fluorescence quantum yield, greater resistance to photobleaching upon direct irradiation, and reduced reactivity toward singlet oxygen. All of these properties are favorable for use of cyanine dyes as fluorescent labels and point toward fluorination as a general strategy for improving performance in imaging applications.     

2,2'-Bipyridinyl carboranes as B,N,N-ligands in cyclometallated complexes of platinum(II)

Novel B,N,N-cyclometallated Pt(II) complexes of 2,2'-bipyridin-6-yl carboranes exhibit absorption and emission similar to relative Pt(II) complexes of aromatic C,N,N-ligands: the same transitions but lower intensities. DFT calculations suggest the former emits from the (3)MLCT state while for the latter the mixed (3)ICT-MLCT transitions should be considered.     

Bis(amino)allenylidene complexes by displacement of the MeO group in methoxy allenylidene complexes of chromium and tungsten. Synthesis, DFT calculations and solid-state structures of new bis(amino)allenylidene complexes

Pentacarbonyl dimethylamino(methoxy)allenylidene tungsten, [(CO)₅WCCC(OMe)NMe₂] (1b), reacts with one equivalent of primary amines, H₂NR, by selectively replacing the methoxy group to give dimethylamino(amino)allenylidene complexes, [(CO)₅WCCC(NHR)NMe₂]. When the amine is used in excess both terminal groups, OMe as well as NMe₂, are replaced by the primary amino group giving [(CO)₅WCCC(NHR)₂ ]. The NHR substituent in these complexes may be modified by deprotonation with LDA followed by alkylation. The replacement of the methoxy group in 1b by a secondary amino group, NR₂, can be achieved by a stepwise process. Addition of Li[NR₂] to the C_γ atom of 1b affords an alkynyl tungstate. Subsequent OMe⁻ elimination induced by TMS-Cl/SiO₂ yields the allenylidene complexes [(CO)₅WCCC(NR₂)NMe₂]. When bidentate diamines are used instead of monoamines both substituents, OMe and NMe₂, are replaced and allenylidene complexes are formed in which C_γ constitutes part of a 5-, 6-, or 7-membered heterocycle. The reaction of [(CO)₅CrCCC(OMe)NMe₂] (1a) with diethylene triamine affords an allenylidene complex with a heterocyclic endgroup carrying a dangling CH₂CH₂NH₂ substituent. All reactions follow a strict regioselective attack of the nucleophile at C_γ and proceed with good to excellent yields. The addition of N-H to the C_αC_β bond is not observed. By applying either one of these routes nearly any substitution pattern in bis(amino)allenylidene complex can be realized.     

Room-temperature phosphorescence and energy transfer in luminescent multinuclear platinum(II) complexes of branched alkynyls

A series of luminescent branched platinum(II) alkynyl complexes, [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]C-C6H4C[triple bond]C}3C6H3] (R=C6H5, C6H4OMe, C6H4Me, C6H4CF3, C5H4N, C6H4SAc, 1-napthyl (Np), 1-pyrenyl (Pyr), 1-anthryl-8-ethynyl (HC[triple bond]CAn)), [1,3-{PyrC[triple chemical bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3], and [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-(HC[triple bond]C)C6H3], was successfully synthesized by using the precursors [1,3,5-{Cl(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] or [1,3-{Cl(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3]. The X-ray crystal structures of [1,3,5-{MeOC6H4C[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] and [1,8-{Cl(PEt3)2PtC[triple bond]C}2An] have been determined. These complexes were found to show long-lived emission in both solution and solid-state phases at room temperature. The emission origin of the branched complexes [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] with R=C6H5, C6H4OMe, C6H4Me, C6H4CF3, C5H4N, and C6H4SAc was tentatively assigned to be derived from triplet states of predominantly intraligand (IL) character with some mixing of metal-to-ligand charge-transfer (MLCT) (dpi(Pt)-->pi*(C[triple bond]CR)) character, while the emission origin of the branched complexes with polyaromatic alkynyl ligands, [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] with R=Np, Pyr, or HC[triple bond]CAn, [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3], [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-(HC[triple bond]C)C6H3], and [1,8-{Cl(PEt3)2PtC[triple bond]C}2An], was tentatively assigned to be derived from the predominantly 3IL states of the respective polyaromatic alkynyl ligands, mixed with some 3MLCT (d(pi)(Pt)-->pi*(C[triple bond]CR)) character. By incorporating different alkynyl ligands into the periphery of these branched complexes, one could readily tune the nature of the lowest energy emissive state and the direction of the excitation energy transfer.     

Enhancement of quantum yield and lifetime of photoinduced chargeseparation for cyclometallated platinum(II) complex/ferricyanide system via Nafion membrane-solution interface

The photoinduced electron transfer from the excited state of cyclometallated platinum(II) complex PtL₁L₂ ²⁺ (L₁=4-methoxyphenyl-6-phenyl-2,2′-bibyridine, L₂=pyridine) incorporated into Nafion membranes to Fe(CN)₆ ^3? in the surrounding solution has been examined. N,N′-tetramethylene-2,2′-bipyridinium (DQ²⁺) entrapped in the Nafion membranes is used as an electron relay. Luminescence quenching studies indicate that the quenching reaction of the excited PtL₁L₂ ²⁺ with DQ²⁺ is static in nature. PtL₁L₂ ³⁺ generated from the luminescence quenching remains in the Nafion matrix, while DQ⁺ migrates by an electron hopping mechanism to the Nafion-water interface, where transfers an electron to Fe(CN)₆ ^3? to produce Fe(CN)₆ ^4?. The negatively charged Fe(CN)₆ ^4? is repelled into the bulk solution by the anionic Nafion surface. The isolation of the photoinduced oxidized species PtL₁L₂ ³⁺ in Nafion from the ultimate reduced species Fe(CN)₆ ^4? in solution prevents them from undergoing back electron transfer. Thus, an extremely long-lived charge separation state is achieved in a high quantum yield.     

Electroluminescence of poly(N-vinylcarbazole) films: fluorescence, phosphorescence and electromers

We have studied the electroluminescence (EL) properties of pure poly(N-vinylcarbazole) (PVK) films. Three types of light emission in the EL spectrum were observed, attributed to fluorescence, phosphorescence and electromers, respectively. The observation of electrophosphorescence from PVK films at room temperature is very meaningful, indicating that PVK can produce a large number of triplet excitons under an electric field at room temperature. Our results demonstrate clearly the reason why PVK is an excellent host material for phosphorescent polymer light-emitting diodes (PLEDs).     

The preparation and analytical evaluation of a new heterogeneous membrane electrode for cadmium(ii)

The preparation of a new cadmium-selective heterogeneous membrane electrode obtained by hot-pressing a mixture of cadmium and silver sulfides with polythene in a moulding press is described. Nernstian response to cadmium ion was achieved only when the mixture of salts was purified by heat treatment at 600° in an atmosphere of hydrogen sulfide for several hours. This behaviour is discussed in terms of the purity of the salts. Interferences and analytical applications in aqueous and nonaqueous solvents are described.     

From a trinuclear platinum(III) phosphido derivative to a platinum(II) cluster: formation of a P-C bond

Reaction of the trinuclear Pt(III)-Pt(III)-Pt(II) [(C6F5)2Pt(III)(mu-PPh2)2Pt(III)(mu-PPh2)2Pt(C6F5)2] (2) derivative with NBu4Br or NBu4I results in the formation of the trinuclear Pt(II) complexes [NBu4][(PPh2C6F5)(C6F5)Pt(mu-PPh2)(mu-X)Pt(mu-PPh2)2Pt(C6F5)2] [X = I (3), Br (4)] through an intramolecular PPh2/C6F5 reductive coupling and the formation of the phosphine PPh2C6F5. The trinuclear Pt(II) complex [(PPh2C6F5)(C6F5)Pt(mu-PPh2)Pt(mu-PPh2)2Pt(C6F5)2] (5), which displays two Pt-Pt bonds, can be obtained either by halide abstraction in 4 or by refluxing of 2 in CH2Cl2. This latter process also implies an intramolecular PPh2/C6F5 reductive coupling. Treatment of complex 5 with several ligands (Br-, H-, and CO) results in the incorporation of the ligand to the cluster and elimination of one (X = H-) or both (X = Br-, CO) Pt-Pt bonds, forming the trinuclear complexes [NBu4][(PPh2C6F5)(C6F5)Pt(mu-PPh2)(mu-X)Pt(mu-PPh2)2Pt(C6F5)2] [X = Br (6), H (7)] or [(PPh2C6F5)(C6F5)Pt(mu-PPh2)2Pt(mu-PPh2)(CO)Pt(C6F5)2(CO)] (8). The structures of the complexes have been established on the basis of 1H, 19F, and 31P NMR data, and the X-ray structures of the complexes 2, 3, 5, and 7 have been established. The chemical relationship between the different complexes has also been studied.     

Anion-dependent fluorescence in bis(anilinoethynyl)pyridine derivatives: switchable ON-OFF and OFF-ON responses

Urea and sulfonamide derivatives of 1 exhibit ON-OFF and OFF-ON switchable fluorescent and colorimetric responses upon protonation. The magnitude of the fluorescence event is dictated by the anion, resulting in a rare, fully organic "turn-on" fluorescent sensor for chloride.