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).
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.
Bright & blue: A strategy for reducing metal‐chelate internal strain enables the preparation of blue emitting iridium(III) carbene complexes (see picture; Ir red, N light blue, F green). The ...phosphorescent OLED fabricated from one of these complexes shows remarkable CIE coordinates of (0.16, 0.13) and peak efficiencies of 6.0 % photons per electron, 6.3 cd A−1, and 4.0 lm W−1.
A series of dialkylated dithienothiophenoquinoids (DTTQs), end‐functionalized with dicyanomethylene units and substituted with different alkyl chains, are synthesized and characterized. Facile ...one‐pot synthesis of the dialkylated DTT core is achieved, which enables the efficient realization of DTTQs as n‐type active semiconductors for solution‐processable organic field effect transistors (OFETs). The molecular structure of hexyl substituted DTTQ‐6 is determined via single‐crystal X‐ray diffraction, revealing DTTQ is a very planar core. The DTTQ cores form a “zig‐zag” linking layer and the layers stack in a “face‐to‐face” arrangement. The very planar core structure, short core stacking distance (3.30 Å), short intermolecular SN distance (2.84 Å), and very low lying lowest unoccupied molecular orbital energy level of −4.2 eV suggest that DTTQs should be excellent electron transport candidates. The physical and electrochemical properties as well as OFETs performance and thin film morphologies of these new DTTQs are systematically studied. Using a solution‐shearing method, DTTQ‐11 exhibits n‐channel transport with the highest mobility of up to 0.45 cm2 V−1 s−1 and a current ON/OFF ratio (ION/IOFF) greater than 105. As such, DTTQ‐11 has the highest electron mobility of any DTT‐based small molecule semiconductors yet discovered combined with excellent ambient stability. Within this family, carrier mobility magnitudes are correlated with the alkyl chain length of the side chain substituents of DTTQs.
Dialkylated dithienothiophenoquinoids (DTTQs) with different alkyl chains and end‐functionalized with dicyanomethylene groups are investigated for organic field effect transistors (OFETs) applications. Remarkably, solution‐sheared DTTQ‐11 OFETs yield the highest mobility of 0.45 cm2 V−1 s−1, good long‐term environmental stability, and electrical stability, which is attractive for solution‐processable n‐type organic semiconductor applications.
Two new for Ru: Unprecedented RuII sensitizers are coordinated by two tridentate ligands, a tricarboxyterpyridine, and a dianionic bis(pyrazolyl)pyridine derivative with an extended π‐conjugated ...auxochrome (see picture, Ru magenta, N blue, O red, F green, S yellow, C gray). This new generation of thiocyanate‐free RuII sensitizers offers solar conversion efficiency in dye‐sensitized solar cells up to η=10.7 %.
Abstract
The pursuit of di-coordinate boron radical has been continued for more than a half century, and their stabilization and structural characterization remains a challenge. Here we report the ...isolation and structural characterization of a linear di-coordinate boron radical cation, achieved by stabilizing the two reactive atomic orbitals of the central boron atom by two orthogonal π-donating and π-accepting functionalities. The electron deficient radical cation undergoes facile one-electron reduction to borylene and binds Lewis base to give heteroleptic tri-coordinate boron radical cation. The co-existence of half-filled and empty p orbitals at boron also allows the CO-regulated electron transfer to be explored. As the introduction of CO promotes the electron transfer from a tri-coordinate neutral boron radical to a boron radical cation, the removal of CO under vacuum furnishes the reverse electron transfer from borylene to yield a solution consisting of two boron radicals.
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