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1.
Molecules ; 25(17)2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32883039

RESUMO

A series of dinuclear copper(I) N,C,N- and P,C,P-carbodiphosphorane (CDP) complexes using multidentate ligands CDP(Py)2 (1) and (CDP(CH2PPh2)2 (13) have been isolated and characterized. Detailed structural information was gained by single-crystal XRD analyses of nine representative examples. The common structural motive is the central double ylidic carbon atom with its characteristic two lone pairs involved in the binding of two geminal L-Cu(I) fragments at Cu-Cu distances in the range 2.55-2.67 Å. In order to enhance conformational rigidity within the characteristic Cu-C-Cu triangle, two types of chelating side arms were symmetrically attached to each phosphorus atom: two 2-pyridyl functions in ligand CDP(Py)2 (1) and its dinuclear copper complexes 2-9 and 11, as well as two diphenylphosphinomethylene functions in ligand CDP(CH2PPh2)2 (13) and its di- and mononuclear complexes 14-18. Neutral complexes were typically obtained via the reaction of 1 with Cu(I) species CuCl, CuI, and CuSPh or via the salt elimination reaction of [(CuCl)2(CDP(Py)2] (2) with sodium carbazolate. Cationic Cu(I) complexes were prepared upon treating 1 with two equivalents of [Cu(NCMe)4]PF6, followed by the addition of either two equivalents of an aryl phosphine (PPh3, P(C6H4OMe)3) or one equivalent of bisphosphine ligands bis[(2-diphenylphosphino)phenyl] ether (DPEPhos), 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (XantPhos), or 1,1'-bis(diphenyl-phosphino) ferrocene (dppf). For the first time, carbodiphosphorane CDP(CH2PPh2)2 (13) could be isolated upon treating its precursor [CH(dppm)2]Cl (12) with NaNH2 in liquid NH3. A protonated and a deprotonated derivative of ligand 13 were prepared, and their coordination was compared to neutral CDP ligand 13. NMR analysis and DFT calculations reveal that the most stable tautomer of 13 does not show a CDP (or carbone) structure in its uncoordinated base form. For most of the prepared complexes, photoluminescence upon irradiation with UV light at room temperature was observed. Quantum yields (ΦPL) were determined to be 36% for dicationic [(CuPPh3)2(CDP(Py)2)](PF6)2 (4) and 60% for neutral [(CuSPh)2(CDP(CH2PPh2)2] (16).

2.
Dalton Trans ; 48(8): 2802-2806, 2019 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-30729248

RESUMO

A highly emissive Ag(i) complex comprising 2,9-dimethyl-1,10-phenanthroline (dmp) and bis[(2-diphenylphosphino)phenyl] ether (dpep) ligands was synthesized, characterized and investigated for its photophysical properties both experimentally and theoretically. The material exhibits intense phosphorescence from the triplet state of ligand centered (3LC) character featuring an unprecedented long lifetime of τ = 110 ms and a quantum yield of ΦPL = 50%, as measured for a doped PMMA matrix under ambient conditions. This is an efficient yet exceptionally slow emission decay, breaking the previous record by several orders of magnitude. Such properties are attributed to two factors: (i) the Ag(i) ion introduces weak spin-orbit coupling and efficient population of the emitting triplet state; (ii) the rigid molecular design combined with a matrix-based rigidity largely suppresses non-radiative relaxations.

3.
Dalton Trans ; 47(47): 17067-17076, 2018 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-30465052

RESUMO

In a previous investigation, it was shown that [Cu(tpym)(PPh3)]PF61 with tpym = tris(2-pyridyl)methane represents a deep blue emitter (λmax = 466 nm) though with a low emission quantum yield ΦPL if doped in a polymer (7%) or dissolved in a fluid solvent (≪1%). In this study, we present new tripod compounds with sterically demanding ligands: [Cu(tpym)(P(o-tol)3)]PF62 and [Cu(tpym)(P(o-butyl-ph)3)]PF63 with P(o-tol)3 = tris(ortho-tolyl)phosphine and P(o-butyl-ph)3 = tris(ortho-n-butylphenyl)phosphine. These compounds show high emission quantum yields even in a fluid solution (dichloromethane) reaching a benchmark value for 3 of ΦPL = 76%. This becomes possible due to the specific design of rigidifying the complexes. Importantly, the deep blue emission color is maintained or even further blue shifted to λmax = 452 nm (compound 3 powder). Compound 2 is characterized photophysically in detail. In particular, it is shown that the lowest excited triplet state T1 experiences very efficient spin-orbit coupling (SOC). Accordingly, the phosphorescence decay rate is as large as 5 × 104 s-1 (20 µs) belonging to the fastest T1→ S0 transition values (shortest decay times) reported so far. Investigations down to T = 1.5 K reveal a large total zero-field splitting (ZFS) of 7 cm-1 (0.9 meV). Although thermally activated delayed fluorescence (TADF) grows in at T≥ 160 K, the phosphorescence of 2 still dominates (60%) over TADF (40%) at ambient temperature. Thus, the compound represents a singlet harvesting-plus-triplet harvesting material, if applied in an OLED.

4.
Phys Chem Chem Phys ; 20(38): 25096-25104, 2018 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-30250953

RESUMO

The temperature dependence (1.7 K < T < 100 K) of emission decay is reported for the first time for a type of di-nuclear Pt complex featuring a metal-metal-to-ligand charge transfer (MMLCT) lowest energy transition that arises from a strong Pt-Pt interaction. The effect of local variation of the host/guest cage in a polymer matrix upon the phosphorescence decay time constants is characterized by the Kohlrausch-Williams-Watts function. The temperature dependence of the average decay time constants is fit by a Boltzmann-type expression to obtain the average zero-field splittings and individual sublevel decay rates of the photoluminescent triplet excited state.

5.
J Phys Chem Lett ; 9(13): 3692-3697, 2018 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-29897780

RESUMO

A highly potent donor-acceptor biaryl thermally activated delayed fluorescence (TADF) dye is accessible by a concise two-step sequence employing two-fold Ullmann arylation and a sequentially Pd-catalyzed Masuda borylation-Suzuki arylation (MBSA). Photophysical investigations show efficient TADF at ambient temperature due to the sterical hindrance between the donor and acceptor moieties. The photoluminescence quantum yield amounts to ΦPL = 80% in toluene and 90% in PMMA arising from prompt and delayed fluorescence with decay times of 21 ns and 30 µs, respectively. From an Arrhenius plot, the energy gap Δ E(S1 - T1) between the lowest excited singlet S1 and triplet T1 state was determined to be 980 cm-1 (120 meV). A new procedure is proposed that allows us to estimate the intersystem crossing time to ∼102 ns.

6.
J Phys Chem Lett ; 9(11): 2848-2856, 2018 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-29750529

RESUMO

The three-fold bridged dinuclear Cu(I) complex Cu2(µ-I)2(1 N- n-butyl-5-diphenyl-phosphino-1,2,4-triazole)3, Cu2I2(P^N)3, shows bright thermally activated delayed fluorescence (TADF) as well as phosphorescence at ambient temperature with a total quantum yield of 85% at an emission decay time of 7 µs. The singlet (S1)-triplet (T1) energy gap is as small as only 430 cm-1 (53 meV). Spin-orbit coupling induces a short-lived phosphorescence with a decay time of 52 µs ( T = 77 K) and a distinct zero-field splitting (ZFS) of T1 into substates by ∼2.5 cm-1 (0.3 meV). Below T ≈ 10 K, effects of spin-lattice relaxation (SLR) are observed and agree with the size of ZFS. According to the combined phosphorescence and TADF, the overall emission decay time is reduced by ∼13% as compared to the TADF-only process. The compound may potentially be applied in solution-processed OLEDs, exploiting both the singlet and triplet harvesting mechanisms.

7.
Chemistry ; 2018 May 29.
Artigo em Inglês | MEDLINE | ID: mdl-29845655

RESUMO

The structural and photophysical properties of a series of new AuI compounds have been studied. The reactions of AuCl(tht) with the phosphanyl- and arsanylboranes RR' EBH2 NMe3 (E=P, As; R=H, Ph; R'=H, Ph, tBu) afford the complexes [AuCl(RR' EBH2 NMe3 )]. In the solid state, [AuCl(H2 PBH2 NMe3 )]2 (2 a) is a dimer showing unsupported intermolecular aurophilic interactions with short Au⋅⋅⋅Au distances. In contrast, [AuCl(H2 AsBH2 NMe3 )]n (2 b) aggregates to form 1D chains. Organic substituents on the pnictogen atoms lead to discrete molecules in [AuCl(RR' PBH2 NMe3 )] (2 c: R=H, R'=tBu; 2 d: R=R'=Ph). To increase the aurophilicity, the ionic homoleptic complexes [Au(RR' EBH2 NMe3 )2 ][AlCl4 ] (3 a-d) have been synthesized, for which 3 a,b form chains in the solid state and exhibit luminescence. The emissions show a drastic redshift with temperature decrease, correlating with decreasing Au⋅⋅⋅Au distances. DFT calculations provide insight into the bonding situation of the products.

8.
J Phys Chem Lett ; 9(4): 702-709, 2018 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-29350932

RESUMO

The dinuclear Ag(I) complex has been designed to show thermally activated delayed fluorescence (TADF) of high efficiency. Strongly electron-donating terminal ligands are introduced to destabilize the d orbitals of the Ag+ ions. Consequently, the orbitals distinctly contribute to the HOMO, whereas the LUMO is localized on the bridging ligand. This ensures charge transfer character of the lowest excited singlet S1 and triplet T1 states. Accordingly, a small energy gap ΔE(S1-T1) is obtained, being essential for TADF behavior. Photophysical investigations show that at ambient temperature the complex exhibits TADF reaching a quantum yield of ΦPL = 70% with the decay time of only τ = 1.9 µs, manifesting one of the fastest TADF decays observed so far. Such an outstanding TADF efficiency is based on a small value of ΔE(S1-T1) = 480 cm-1 combined with a large transition rate of k(S1 → S0) = 2.2 × 107 s-1.

9.
Inorg Chem ; 56(21): 13274-13285, 2017 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-29053269

RESUMO

The four new Ag(I) complexes Ag(phen)(P2-nCB) (1), Ag(idmp)(P2-nCB) (2), Ag(dmp)(P2-nCB) (3), and Ag(dbp)(P2-nCB) (4) with P2-nCB = bis(diphenylphosphine)-nido-carborane, phen = 1,10-phenanthroline, idmp = 4,7-dimethyl-1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline, and dbp = 2,9-di-n-butyl-1,10-phenanthroline were designed to demonstrate how to develop Ag(I) complexes that exhibit highly efficient thermally activated delayed fluorescence (TADF). The substituents on the 1,10-phenanthroline ligand affect the photophysical properties strongly (i) electronically via influencing the radiative rate of the S1 → S0 transition and (ii) structurally by rigidifying the molecular geometry with respect to geometry changes occurring in the lowest excited S1 and T1 states. The oscillator strength of the S1 ↔ S0 transition f(S1 ↔ S0)-an important parameter for the TADF efficiency being proportional to the radiative rate-can be increased from f(S1 ↔ S0) = 0.0258 for Ag(phen)(P2-nCB) (1) to f(S1 ↔ S0) = 0.0536 for Ag(dbp)(P2-nCB) (4), as calculated for the T1 state optimized geometries. This parameter governs the radiative TADF decay time (τr) at ambient temperature, found to be τr = 5.6 µs for Ag(phen)(P2-nCB) (1) but only τr = 1.4 µs for Ag(dbp)(P2-nCB) (4)-a record TADF value. In parallel, the photoluminescence quantum yield (ΦPL) measured for powder samples at ambient temperature is boosted up from ΦPL = 36% for Ag(phen)(P2-nCB) (1) to ΦPL = 100% for Ag(dbp)(P2-nCB) (4). This is a consequence of a cooperative effect of both decreasing the nonradiative decay rate and increasing the radiative decay rate in the series from Ag(phen)(P2-nCB) (1), Ag(idmp)(P2-nCB) (2), and Ag(dmp)(P2-nCB) (3) to Ag(dbp)(P2-nCB) (4). Another parameter important for the TADF behavior is the activation energy of the S1 state from the state T1, ΔE(S1-T1). Experimentally it is determined for the complexes Ag(dmp)(P2-nCB) (3) and Ag(dbp)(P2-nCB) (4) to be of moderate size of ΔE(S1-T1) = 650 cm-1.

10.
Chemphyschem ; 18(24): 3508-3535, 2017 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-29083512

RESUMO

The development of organic light emitting diodes (OLEDs) and the use of emitting molecules have strongly stimulated scientific research of emitting compounds. In particular, for OLEDs it is required to harvest all singlet and triplet excitons that are generated in the emission layer. This can be achieved using the so-called triplet harvesting mechanism. However, the materials to be applied are based on high-cost rare metals and therefore, it has been proposed already more than one decade ago by our group to use the effect of thermally activated delayed fluorescence (TADF) to harvest all generated excitons in the lowest excited singlet state S1 . In this situation, the resulting emission is an S1 →S0 fluorescence, though a delayed one. Hence, this mechanism represents the singlet harvesting mechanism. Using this effect, high-cost and strong SOC-carrying rare metals are not required. This mechanism can very effectively be realized by use of CuI or AgI complexes and even by purely organic molecules. In this investigation, we focus on photoluminescence properties and on crucial requirements for designing CuI and AgI materials that exhibit short TADF decay times at high emission quantum yields. The decay times should be as short as possible to minimize non-radiative quenching and, in particular, chemical reactions that frequently occur in the excited state. Thus, a short TADF decay time can strongly increase the material's long-term stability. Here, we study crucial parameters and analyze their impact on the TADF decay time. For example, the energy separation ΔE(S1 -T1 ) between the lowest excited singlet state S1 and the triplet state T1 should be small. Accordingly, we present detailed photophysical properties of two case-study materials designed to exhibit a large ΔE(S1 -T1 ) value of 1000 cm-1 (120 meV) and, for comparison, a small one of 370 cm-1 (46 meV). From these studies-extended by investigations of many other CuI TADF compounds-we can conclude that just small ΔE(S1 -T1 ) is not a sufficient requirement for short TADF decay times. High allowedness of the transition from the emitting S1 state to the electronic ground state S0 , expressed by the radiative rate kr (S1 →S0 ) or the oscillator strength f(S1 →S0 ), is also very important. However, mostly small ΔE(S1 -T1 ) is related to small kr (S1 →S0 ). This relation results from an experimental investigation of a large number of CuI complexes and basic quantum mechanical considerations. As a consequence, a reduction of τ(TADF) to below a few µs might be problematic. However, new materials can be designed for which this disadvantage is not prevailing. A new TADF compound, Ag(dbp)(P2 -nCB) (with dbp=2,9-di-n-butyl-1,10-phenanthroline and P2 -nCB=bis-(diphenylphosphine)-nido-carborane) seems to represent such an example. Accordingly, this material shows TADF record properties, such as short TADF decay time at high emission quantum yield. These properties are based (i) on geometry optimizations of the AgI complex for a fast radiative S1 →S0 rate and (ii) on restricting the extent of geometry reorganizations after excitation for reducing non-radiative relaxation and emission quenching. Indeed, we could design a TADF material with breakthrough properties showing τ(TADF)=1.4 µs at 100 % emission quantum yield.

11.
Top Curr Chem (Cham) ; 374(3): 25, 2016 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-27573265

RESUMO

Molecules that exhibit thermally activated delayed fluorescence (TADF) represent a very promising emitter class for application in electroluminescent devices since all electrically generated excitons can be transferred into light according to the singlet harvesting mechanism. Cu(I) compounds are an important class of TADF emitters. In this contribution, we want to give a deeper insight into the photophysical properties of this material class and demonstrate how the emission properties depend on molecular and host rigidity. Moreover, we show that with molecular optimization a significant improvement of selected emission properties can be achieved. From the discussed materials, we select one specific dinuclear complex, for which the two Cu(I) centers are four-fold bridged to fabricate an organic light emitting diode (OLED). This device shows the highest efficiency (of 23 % external quantum efficiency) reported so far for OLEDs based on Cu(I) emitters.


Assuntos
Complexos de Coordenação/química , Cobre/química , Luminescência , Teoria Quântica , Temperatura
12.
Inorg Chem ; 55(5): 2441-9, 2016 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-26909653

RESUMO

High-resolution fluorescence, phosphorescence, as well as related excitation spectra, and, in particular, the emission decay behavior of solid [Bu4N]4[Pt2(µ-P2O5(BF2)2)4], abbreviated Pt(pop-BF2), have been investigated over a wide temperature range, 1.3-310 K. We focus on the lowest excited states that result from dσ*pσ (5dz(2)-6pz) excitations, i.e., the singlet state S1 (of (1)A2u symmetry in D4h) and the lowest triplet T1, which splits into spin-orbit substates A1u((3)A2u) and Eu((3)A2u). After optical excitation, an unusually slow intersystem crossing (ISC) is observed. As a consequence, the compound shows efficient dual emission, consisting of blue fluorescence and green phosphorescence with an overall emission quantum yield of ∼ 100% over the investigated temperature range. Our investigation sheds light on this extraordinary dual emission behavior, which is unique for a heavy-atom transition metal compound. Direct ISC processes in Pt(pop-BF2) are largely forbidden due to spin-, symmetry-, and Franck-Condon overlap-restrictions and, therefore, the ISC time is as long as 29 ns for T < 100 K. With temperature increase, two different thermally activated pathways, albeit still relatively slow, are promoted by spin-vibronic and vibronic mechanisms, respectively. Thus, distinct temperature dependence of the ISC processes results and, as a consequence, also of the fluorescence/phosphorescence intensity ratio. The phosphorescence lifetime also is temperature-dependent, reflecting the relative population of the triplet T1 substates Eu and A1u. The highly resolved phosphorescence shows a ∼ 220 cm(-1) red shift below 10 K, attributable to zero-field splitting of 40 cm(-1) plus a promoting vibration of 180 cm(-1).

13.
Dalton Trans ; 44(46): 20045-55, 2015 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-26525145

RESUMO

Three deep blue emitting Cu(I) compounds, [Cu(PPh3)tpym]PF6, [Cu(PPh3)tpym]BF4, and [Cu(PPh3)tpym]BPh4 (tpym = tris(2-pyridyl)methane, PPh3 = triphenylphosphine) featuring the tripodally coordinating tpym and the monodentate PPh3 ligands were studied with regard to their structural and photophysical properties. The compounds only differ in their respective counter ions which have a strong impact on the emission properties of the powder samples. For example, the emission quantum yield can be significantly increased for the neat material from less than 10% to more than 40% by exchanging BPh4(-) with PF6(-). These effects can be linked to different molecular packings which depend on the counter ion. In agreement with these results, it was found that the emission properties also strongly depend on the surrounding matrix environment which was elucidated by investigating photophysical properties of the compounds as powders, doped into a polymer matrix, and dissolved in a fluid solution, respectively. The observed differences in the emission behavior can be explained by different and pronounced distortions that occur in the excited state. These distortions are also displayed by density functional theory (DFT) calculations.

14.
Dalton Trans ; 44(44): 19305-13, 2015 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-26491939

RESUMO

Two compounds 1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane catena-tetra-µ-halo-dicuprate(I) with DABCOMe2 Cu2X4 (1: X = Br, 2: X = I) were synthesized by hydrothermal reaction of copper(I) halides with the corresponding 1,4-diazoniabicyclo[2.2.2]octane (DABCO) dihydrohalides in an acetonitrile/methanol mixture. Both compounds crystallize monoclinically, 1 with a = 9.169(4) Å, b = 10.916(6) Å, c = 15.349(6) Å, ß = 93.93(2)°, V = 1533(1) Å(3), Z = 4, space group P2(1)/n (no. 14) and 2 with a = 15.826(9) Å, b = 9.476(5) Å, c = 22.90(2) Å, ß = 90.56(5)°, V = 3434(5) Å(3), Z = 8, space group P2(1) (no. 4), respectively (lattice constants refined from powder diffraction data measured at 293 K). The cations in both compounds are formed by in situ N-methylation of DABCOH2(2+) cations by methanol in a S(N)2 reaction. Both compounds contain an anionic copper(I) halide chain structure consisting of trans edge-sharing CuX4 tetrahedra. The chains are strongly kinked at every 2(nd) junction thus forming a zigzag structure. The shortest halide-halide distances are observed between the halide ions of adjacent tetrahedra which are approaching each other due to the kinking. This structure type shows a specific luminescence behavior. Under optical excitation, the compounds exhibit yellow (1) and green (2) emission with photoluminescence quantum yields of Φ(PL) = 52 and 4%, respectively, at ambient temperature. According to DFT and TDDFT calculations, the emission is assigned to be a phosphorescence essentially involving a metal centered transition between the HOMO consisting mainly of copper 3d and halide p orbitals and the LUMO consisting mainly of copper 4s and 4p orbitals. The temperature dependence of the emission spectra, decay times, and quantum yields has been investigated in detail, especially for 1. From the resulting trends it can be concluded that the emission for T≤ 100 K stems from energetically lower lying copper halide segments. Such segments represent the structural motif of the halocuprate(I) chains. With increasing temperature energetically higher lying segments are populated which also emit, but open the pathway for thermally activated energy transfer to quenching defects.

15.
Inorg Chem ; 54(9): 4322-7, 2015 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-25894718

RESUMO

A comparison of three copper(I) compounds [1, Cu(dppb)(pz2Bph2); 2, Cu(pop)(pz2Bph2); 3, Cu(dmp)(phanephos)(+)] that show pronounced thermally activated delayed fluorescence (TADF) at ambient temperature demonstrates a wide diversity of emission behavior. In this study, we focus on compound 1. A computational density functional theory (DFT)/time-dependent DFT approach allows us to predict detailed photophysical properties, while experimental emission studies over a wide temperature range down to T = 1.5 K lead to better insight into the electronic structures even with respect to spin-orbit coupling efficiencies, radiative rates, and zero-field splitting of the triplet state. All three compounds, with emission quantum yields higher than ϕPL = 70%, are potentially well suited as emitters for organic light-emitting diodes (OLEDs) based on the singlet-harvesting mechanism. Interestingly, compound 1 is by far the most attractive one because of a very small energy separation between the lowest excited singlet S1 and triplet T1 state of ΔE(S1-T1) = 370 cm(-1) (46 meV). Such a small value has not been reported so far. It is responsible for the very short decay time of τ(TADF, 300 K) = 3.3 µs. Hence, if focused on the requirements of a short TADF decay time for reduction of the saturation effects in OLEDs, copper(I) complexes are well comparable or even slightly better than the best purely organic TADF emitters.

16.
Angew Chem Int Ed Engl ; 54(16): 4963-7, 2015 Apr 13.
Artigo em Inglês | MEDLINE | ID: mdl-25703020

RESUMO

A novel approach is presented for the encapsulation of organic functional molecules between two sheets of 1 nm thin silicate layers, which like glass are transparent and chemically stable. An ordered heterostructure with organic interlayers strictly alternating with osmotically swelling sodium interlayers can be spontaneously delaminated into double stacks with the organic interlayers sandwiched between two silicate layers. The double stacks show high aspect ratios of >1000 (typical lateral extension 5000 nm, thickness 4.5 nm). This newly developed technique can be used to mask hydrophobic functional molecules and render them completely dispersible in water. The combination of the structural anisotropy of the silicate layers and a preferred orientation of molecules confined in the interlayer space allows polymer nanocomposite films to be cast with a well-defined orientation of the encapsulated molecules, thus rendering the optical properties of the nanocoatings anisotropic.

17.
Small ; 11(7): 792-6, 2015 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-25315068

RESUMO

A nano confinement strategy is presented to control the spatial orientation and emission polarization of phosphorescent metal complexes. Through nano-confinement of the phosphorescent metal complex [Ru(bpy)3 ](2+) by attaching it to anionic clay nanoplatelets, it is possible to simultaneously lock the spatial orientation of the complex and fix its emission polarization. This quasi-epitaxial approach may provide a future work strategy directed at light emitting diodes and lasers.

18.
Dalton Trans ; 44(18): 8506-20, 2015 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-25434594

RESUMO

A new class of emissive and neutral Cu(I) compounds with tripodal ligands is presented. The complexes were characterized chemically, computationally, and photophysically. Under ambient conditions, the powders of the compounds exhibit yellow to red emission with quantum yields ranging from about 5% to 35%. The emission represents a thermally activated delayed fluorescence (TADF) combined with a short-lived phosphorescence which represents a rare situation and is a consequence of high spin-orbit coupling (SOC). In the series of the investigated compounds the non-radiative rates increase with decreasing emission energy according to the energy gap law while the radiative rate is almost constant. Furthermore, a well-fit linear dependence between the experimental emission energies and the transition energies calculated by DFT and TD-DFT methods could be established, thus supporting the applicability of these computational methods also to Cu(I) complexes.

19.
J Am Chem Soc ; 137(1): 399-404, 2015 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-25486064

RESUMO

Luminescent materials showing thermally activated delayed fluorescence (TADF) have gained high attractiveness as emitters in organic light emitting diodes (OLEDs) and other photonic applications. Nevertheless, even utilization of TADF can be further improved, introducing a novel concept. This is demonstrated by a new class of brightly luminescent low-cost Cu(I) compounds, for which the emission stems from both the lowest excited triplet T1 and singlet S1 state. At T = 300 K, these materials exhibit quantum yields of more than ΦPL = 90% at short emission decay times. About 80% of the emission intensity stems from the singlet due to TADF, but importantly, an additional 20% is contributed by the lower lying triplet state according to effective spin-orbit coupling (SOC). SOC induces also a relatively large zero-field splitting of the triplet being unusual for Cu(I) complexes. Thus, the overall emission decay time is distinctly reduced. Combined use of both decay paths opens novel photonic applications, in particular, for OLEDs.

20.
J Am Chem Soc ; 136(45): 16032-8, 2014 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-25260042

RESUMO

Photophysical properties of two highly emissive three-coordinate Cu(I) complexes, (IPr)Cu(py2-BMe2) (1) and (Bzl-3,5Me)Cu(py2-BMe2) (2), with two different N-heterocyclic (NHC) ligands were investigated in detail (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; Bzl-3,5Me = 1,3-bis(3,5-dimethylphenyl)-1H-benzo[d]imidazol-2-ylidene; py2-BMe2 = di(2-pyridyl)dimethylborate). The compounds exhibit remarkably high emission quantum yields of more than 70% in the powder phase. Despite similar chemical structures of both complexes, only compound 1 exhibits thermally activated delayed blue fluorescence (TADF), whereas compound 2 shows a pure, yellow phosphorescence. This behavior is related to the torsion angles between the two ligands. Changing this angle has a huge impact on the energy splitting between the first excited singlet state S1 and triplet state T1 and therefore on the TADF properties. In addition, it was found that, in both compounds, spin-orbit coupling (SOC) is particularly effective compared to other Cu(I) complexes. This is reflected in short emission decay times of the triplet states of only 34 µs (1) and 21 µs (2), respectively, as well as in the zero-field splittings of the triplet states amounting to 4 cm(-1) (0.5 meV) for 1 and 5 cm(-1) (0.6 meV) for 2. Accordingly, at ambient temperature, compound 1 exhibits two radiative decay paths which are thermally equilibrated: one via the S1 state as TADF path (62%) and one via the T1 state as phosphorescence path (38%). Thus, if this material is applied in an organic light-emitting diode, the generated excitons are harvested mainly in the singlet state, but to a significant portion also in the triplet state. This novel mechanism based on two separate radiative decay paths reduces the overall emission decay time distinctly.

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