Organic light‐emitting diodes with external quantum efficiency of 38.8% are realized using a Pt‐based thin‐film emitting layer with photoluminescence quantum yield of 96% and transition dipole ratio ...of 93%. The emitting dipole orientation of the thin films fabricated using Pt complexes is investigated and the structural relationship between X‐ray structural analysis and the structures in thin films are discussed based on quantum chemical calculations.
A new class of neutral bis‐tridentate Ir(III) metal complexes that show nearly unitary red, green, and blue emissions in solution is prepared and employed for the fabrication of both monochrome and ...white‐emitting organic light‐emitting diodes, among which a green device gives external quantum efficiency exceeding 31%.
Emissive Ir(III) metal complexes possessing two tridentate chelates (bis‐tridentate) are known to be more robust compared to those with three bidentate chelates (tris‐bidentate). Here, the ...deep‐blue‐emitting, bis‐tridentate Ir(III) metal phosphors bearing both the dicarbene pincer ancillary such as 2,6‐diimidazolylidene benzene and the 6‐pyrazolyl‐2‐phenoxylpyridine chromophoric chelate are synthesized. A deep‐blue organic light‐emitting diode from one phosphor exhibits Commission Internationale de l'Eclairage (CIE(x,y)) coordinates of (0.15, 0.17) with maximum external quantum efficiency (max. EQE) of 20.7% and EQE = 14.6% at the practical brightness of 100 cd m−2.
A deep‐blue organic light‐emitting diode (OLED) from one bis‐tridentate Ir(III) phosphor 5 exhibits CIE(x,y) coordinates of (0.15, 0.17) with maximum external quantum efficiency (max. EQE) of 20.7% and EQE = 14.6% at the practical brightness of 100 cd m−2.
A new series of molecules, T1–T4, possessing thermally activated delayed fluorescence (TADF) have been strategically designed and synthesized. Molecules T1–T4 contain the dimethyl acridine as the ...electron donor, which is linked to either symmetrical or unsymmetrical diphenyl pyrimidine as an acceptor. In comparison to the ubiquitous triazine acceptor, the selection of pyrimidine as an acceptor has advantages of facile functionalization and less stabilized unoccupied π orbitals, so that the energy gap toward the blue region can be accessed. Together with acridine donors, the resulting donor–acceptor functional materials reveal remarkable TADF properties. In the solid state, molecules T1–T4 all exhibit intriguing mechanochromism. The crystal structures, together with spectroscopy and dynamics acquired upon application of stressing, lead us to propose two types of structural arrangement that give distinct emission properties, one with and the other without TADF. Upon fabricating organic light‐emitting diodes, the T1–T4 films prepared from sublimation all exhibit dominant TADF behavior; this accounts for their high performance: an electroluminescent emission at λ=490 nm, with an external quantum efficiency of 14.2 %, can be attained when T2 is used as an emitter.
Functional pyrimidine acceptors: A new series of molecules, T1–T4, possessing thermally activated delayed fluorescence (TADF) have been strategically designed and synthesized. Together with acridine donors, the resulting donor– acceptor functional materials reveal remarkable TADF properties. In the solid state, molecules T1–T4 also exhibit intriguing mechanochromism (see figure).
Multiple‐stimuli‐responsive photoluminescence films based on a ZnII–organic framework, {Zn2(Htpim)(3,4‐pydc)2⋅4 DMF⋅4 H2O}n (1, Htpim=2,4,5‐tri(4‐pyridyl)imidazole, ...3,4‐H2pydc=3,4‐pyridinedicarboxylic acid), were fabricated. This compound consisted of a 2D corrugated layer, {Zn(3,4‐pydc)}n, which was further pillared using a Y‐shaped pillar N‐donor ligand (Htpim) to form a 3D‐pillared‐layer framework with 1D open channels. The rectangular channels in the as‐synthesized compound are fully occupied by guest DMF and H2O molecules. The framework exhibits instant and reversible thermochromic properties corresponding to the removal of different H2O and DMF guest molecules as temperature increases. The pale‐yellow crystal undergoes significant redshifting to a greenish emission centered at 530 nm. Compound 1 also showed remarkable solvatochromic effects in the presence of various organic solvents without affecting its structural integrity. In addition, polycrystalline MOF films were grown on an α‐Al2O3 support for switchable and fast‐response thermochromic and solvatochromic sensors.
Multiple‐stimuli‐responsive photoluminescence films based on a ZnII–organic framework were fabricated. The framework exhibits instant and reversible thermochromic properties corresponding to the removal of different H2O and DMF guest molecules as temperature increases. The pale‐yellow crystal undergoes significant redshifting to a greenish emission centered at 530 nm (see figure).
Pt(II) metal complexes are known to exhibit strong solid‐state aggregation and are promising for realization of efficient emission in fabrication of organic light emitting diodes (OLED) with nondoped ...emitter layer. Four pyrimidine–pyrazolate based chelates, together with four isomeric Pt(II) metal complexes, namely: Pt(pm2z)2, Pt(tpm2z)2, Pt(pm4z)2, and Pt(tpm4z)2, are isolated and systematically investigated for their structure–property relationships for practical OLED applications. Detailed single molecular and aggregated structures are revealed by photophysical and mechanochromic measurements, grazing‐incidence X‐ray diffraction, and theoretical approaches. These results suggest that these Pt(II) emitters pack like a deck of playing cards under vacuum deposition, and their emission energy is not only affected by the single molecular designs, but notably influenced by their intermolecular packing interaction, i.e., Pt···Pt separations that are arranged in the order: Pt(tpm4z)2 > Pt(pm4z)2 > Pt(tpm2z)2 > Pt(pm2z)2. Nondoped OLED with emission ranging from green to red are prepared, to which the best performances are recorded for Pt(tpm2z)2, giving maximum external quantum efficiency (EQE) of 27.5% at 103 cd m−2, maximum luminance of 2.5 × 105 cd m−2 at 17 V, and with stable CIEx,y of (0.56, 0.44).
Nondoped organic light emitting diodes (OLED) devices with emission ranging from green to red are prepared using four Pt(II) complexes that exhibit strong solid‐state aggregation and horizontal aligned transition dipole moments, while their stacking characteristics also play a crucial role in manipulating the emission properties.
The effect of heteroalkyl (‐XR, X = Se, S, O) substitution on a series of molecular semiconductors having a 3,3′‐diheteroalkyl‐2,2′‐bithiophene (XBT) central core is studied. Thus, the ...selenotetradecyl (‐SeC14H29) SeBT core is investigated by end‐functionalization with two dithienothiophene (DTT), thienothiophene (TT), and thiophene (T) units to give SeBTs 1–3, respectively, for molecular π‐conjugation effect examination. Furthermore, the selenodecyl (‐SeC10H21) and selenohexyl (‐SeC6H13) SeBT cores end‐capped with DTTs to give SeBTs 1B and 1C, respectively, are synthesized for understanding ‐SeR length effects. To address systematically the impact of the chalcogen heteroatom, the newly developed selenoalkyl SeBTs are compared with the previously reported thiotetradecyl (‐SC14H29) DDTT‐SBT (4) and the new tetradecyloxy (‐OC14H29) DDTT‐OBT (5). When fabricating organic field effect transistors by the solution‐shearing method, the devices based on the tetradecylated DDTT‐SeBT (1) exhibit the highest mobility up to 4.01 cm2 V−1 s−1, which is larger than those of the other SeBT compounds and both DDTT‐SBT (4) (1.70 cm2 V−1 s−1) and DDTT‐OBT (5) (9.32 × 10−4 cm2 V−1 s−1). These results are rationalized by a combination of crystallographic, morphological, and microstructural analysis.
The effect of heteroalkyl (‐XR, X = O, S, Se) substitution on a series of small molecule semiconductors having a 3,3′‐diheteroalkyl‐2,2′‐bithiophene central cores are studied. Solution‐processed DDTT‐SeBT (1) organic field effect transistors exhibit high hole mobility of 4.01 cm2 V−1 s−1, far surpassing those of the corresponding SBT and OBT compounds.
The first regioselective, diastereoselective, and enantioselective organocatalyzed Michael–Michael cascade of vinylogous ketone enolates and nitroalkenes for the construction of fully substituted ...cyclobutanes is achieved by the deployment of the appropriate chiral squaramide catalyst and the pertinent substituent on the substrate. The domino reaction provided cyclobutanes with four contiguous stereocenters, including a quaternary center in good yields with diastereomeric ratio of >20:1 and with enantioselectivities of mostly up to 98% enantiomeric excess (ee). The structures and the absolute configurations of the adducts were confirmed by single-crystal X-ray crystallographic analyses of the appropriate products.
We report the synthesis of a novel heteroheptanuclear metal string complex (HMSC) Ni
3
Ru
2
Ni
2
(μ
7
-teptra)
4
(NCS)
2
(PF
6
)
1
supported by tetra-pyridyl-tri-amine (H
3
teptra) ligands. We ...employed X-ray diffraction and other spectroscopic techniques to characterize the complex. The observed remarkably short Ru-Ru distance of 2.2499(3) Å for
1
is indicative of a unique metal-metal interaction in the mixed-valence Ru
2
5+
(
S
= 3/2) unit. The complex exhibits a relatively high magnetic moment value of 4.55 B.M. at 4 K, which increases rapidly to 6.00 B.M. at 30 K and remains at 6.11 B.M. from 50 to 300 K as shown by SQUID measurements, indicating a high spin (
S
≥ 3/2) system which is further supported by the analyses of EPR spectra at low temperatures. These magnetic behaviors can be ascribed to the result of spin-exchange interactions among multi-spin centers.
A novel heteroheptanuclear metal string complex was synthesized by using nickel and ruthenium metal ions to explore the electronic structure and magnetic property.
Using a semi-flexible quadritopic N-donor ligand, 5,5'-bipyrimidine (bpym), four new azide-based coordination polymers, {Co2(bpym)(N3)4·MeCN}n (1), Co(bpym)(N3)2n (2), Mn(bpym)(N3)2n (3) and ...{Ni3(bpym)3(N3)6·2H2O}n (4) were synthesized and structurally characterized. With bpym aciting as a planar μ4-bridging ligand, the resulting compound, 1, comprised a net-to-net 3D framework composed of two grid-like 44-subnets, Co(EE-N3)2-based and Co2(bpym)-based sheets, with a (4,6)-connected (42·64)(48·66·8)2 topology. Compound 2 adopted a 3D pillared-layer framework with a pts topology based on six-connected Co(ii) centers and four-connected twisted μ4-bpym ligands, while compound 3 adopted a 3D pillared-layer structure with a bcu topology based on Co(EE-N3)2-based 44-layers and two-connected twisted μ2-bpym pillars. In contrast, compound 4 had a 2D layered structure composed of 1D Ni(ii) chains with alternating double EE-N3 and double EO-N3 bridges in an EE-EE-EO sequence and two-connected bpym linkers. The magnetic properties of 1-4 were investigated. The findings indicate that 1 showed weak ferromagnetism due to spin-canted antiferromagnetism and long-range magnetic ordering with a critical temperature, TC = 12.6 K. In contrast, compound 2 exhibited weak ferromagnetism due to spin-canted antiferromagnetism and antiferromagnetic ordering. In compound 3, antiferromagnetic interactions dominated between the Mn(ii) centers through the EE-N3 bridges. In compound 4, the antiferromagnetic and ferromagnetic interactions were transmitted through double EE-N3 and double EO-N3 bridges, respectively, resulting in an AF-AF-F topological ferrimagnetic Ni(ii) chain. Furthermore, field-induced magnetic phase transitions of metamagnetism for 2 and 4 were also observed below TN = 3.6 K and 8.2 K, respectively.
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