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Cyclometalated Pt(II) complexes are popular phosphorescent emitters with color-tunable emissions. To render their practical applications as organic light-emitting diodes emitters, it is required to develop Pt(II) complexes with high radiative decay rate constant and photoluminescence (PL) quantum yield. Here, a general protocol is developed for accurate predictions of emission wavelength, radiative decay rate constant, and PL quantum yield based on the combination of first-principles quantum mechanical method, machine learning, and experimental calibration. A new dataset concerning phosphorescent Pt(II) emitters is constructed, with more than 200 samples collected from the literature. Features containing pertinent electronic properties of the complexes are chosen and ensemble learning models combined with stacking-based approaches exhibit the best performance, where the values of squared correlation coefficients are 0.96, 0.81, and 0.67 for the predictions of emission wavelength, PL quantum yield and radiative decay rate constant, respectively. The accuracy of the protocol is further confirmed using 24 recently reported Pt(II) complexes, which demonstrates its reliability for a broad palette of Pt(II) emitters.
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It is vital to develop highly efficient non-doped blue organic light-emitting diodes (OLEDs) with high color purity and low-efficiency roll-off for applications in display and lighting. Herein, two blue D-A fluorophores TPA-PO and TPA-DPO are designed and synthesized, in which phenanthro[9,10-d]oxazole (PO) acts as the acceptor and triphenylamine as the donor. TPA-PO and TPA-DPO display good thermal stability and efficient luminescence efficiency in neat film. Results based on photophysical property and theoretical calculation demonstrate that TPA-PO and TPA-DPO possess the hybridized local and charge-transfer (HLCT) feature, which can utilize the triplet exciton to achieve highly efficient electroluminance (EL). The non-doped OLEDs with TPA-PO/TPA-DPO as pure emissive layer show the uniform EL emission peak at 468â nm, corresponding to CIE coordinates of (0.168, 0.187) and (0.167, 0.167), respectively. The TPA-DPO-based non-doped OLEDs provide the maximum external quantum efficiency (EQE) of 7.99 % and high exciton utility efficiency of 48.4 %~72.6 %. Moreover, the TPA-DPO-based device exhibits low-efficiency roll-off, still maintaining the EQE of 6.03 % at the high luminance of 5000â cd m-2. Those findings state clearly that PO is a promising building block of blue fluorophore with a potential HLCT feature to be applied in non-doped OLEDs.
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Hybridized local and charge-transfer (HLCT) with the utilization of both singlet and triplet excitons through the "hot excitons" channel have great application potential in highly efficient blue organic light-emitting diodes (OLEDs). The proportion of charge-transfer (CT) and locally excited (LE) components in the relevant singlet and triplet states makes a big difference for the high-lying reverse intersystem crossing process. Herein, three novel donor (D)-acceptor (A) type HLCT materials, 7-([1,1'-biphenyl]-4-yl(9,9-dimethyl-9H-fluoren-2-yl)amino)-3-phenyl-1H-isochromen-1-one (pPh-7P), 7-([1,1'-biphenyl]-4-yl(9,9-dimethyl-9H-fluoren-2-yl)amino)-3-methyl-1H-isochromen-1-one (pPh-7M), and 6-([1,1'-biphenyl]-4-yl(9,9-dimethyl-9H-fluoren-2-yl)amino)-3-methyl-1H-isochromen-1-one (pPh-6M), were rationally designed and synthesized with diphenylamine derivative as donor and oxygen heterocyclic coumarin moiety as acceptors. The proportions of CT and LE components were fine controlled by changing the connection site of diphenylamine derivative at C6/C7-position and the substituent at C3-position of coumarin moiety. The HLCT characteristics of pPh-7P, pPh-7M, and pPh-6M were systematically demonstrated through photophysical properties and density functional theory calculations. The solution-processed doped OLEDs based on pPh-6M exhibited deep-blue electroluminescence with the maximum emission wavelength of 446â nm, maximum luminance of 8755â cd m-2, maximum current efficiency of 5.83â cd A-1, and maximum external quantum efficiency of 6.54 %. The results reveal that pPh-6M with dominant 1LE and 3CT components has better OLED performance.
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Luminescent organometallic complexes of earth-abundant copper(I) have long been studied in organic light-emitting diodes (OLED). Particularly, Cu(I)-based carbene-metal-amide (CMA) complexes have recently emerged as promising organometallic emitters. However, blue-emitting Cu(I) CMA complexes have been rarely reported. Here we constructed two blue-emitting Cu(I) CMA emitters, MAC*-Cu-CF3Cz and MAC*-Cu-2CF3Cz, by introducing one or two CF3 substitutes into carbazole ligands. Both complexes exhibited high thermal stability and blue emission colors. Moreover, two complexes exhibited different emission origins rooting from different donor ligands: a distinct thermally activated delayed fluorescence (TADF) from ligand-to-ligand charge transfer excited states for MAC*-Cu-CF3Cz or a dominant phosphorescence nature from local triplet excited state of the carbazole ligand for MAC*-Cu-2CF3Cz. Inspiringly, MAC*-Cu-CF3Cz had high photoluminescence quantum yields of up to 94 % and short emission lifetimes of down to 1.2â µs in doped films, accompanied by relatively high radiative rates in the 105â s-1 order. The resultant vacuum-deposited OLEDs based on MAC*-Cu-CF3Cz delivered pure-blue electroluminescence at 462â nm together with a high external quantum efficiency of 13.0 %.
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Near-infrared (NIR) light has characteristics of invisibility to human eyes, less background interference, low light scattering, and strong cell penetration. Therefore, NIR luminescent materials have significant applications in imaging, sensing, energy, information storage and display. The development of NIR luminescent materials thus has emerged as a highly dynamic area of research in the realm of contemporary materials. To date, NIR luminescent materials are roughly divided into inorganic materials and organic materials. Compared with inorganic materials, organic NIR luminescent materials have become a hot research topic in recent years due to their rich sources, easy control of structure, simple preparation process, low cost, and good film-forming properties. Among them, iridium(III) [Ir(III)] complexes exhibit excellent properties such as thermal stability, simple synthesis, easy color modulation, short excited state lifetimes, and high brightness, thus becoming one of the ideal luminescent material systems for preparing high-quality organic light-emitting diodes. Therefore, how to obtain Ir(III) complexes with NIR emission and high efficiency through molecular design is a necessary and promising research topic. This work reviews the research progress of representative NIR Ir(III) complexes bearing isoquinoline-, phenazine-, and phthalazine-based ligands reported in recent years and introduces the design strategies and electroluminescent performances of NIR Ir(III) complexes.
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The electronic and optoelectronic properties of molecules constituted by benzene as linker, phenoxaborin as acceptor coupled with different types of donor moieties are investigated using the density functional theoretical method. The energy gap between the first excited singlet and triplet states (ΔEST) of the designed molecules (1-9) is found to be less than 0.5 eV suggesting them as ideal candidates for thermally activated delayed fluorescence (TADF) emitters. The analysis of frontier molecular orbitals of the molecules revealed a minimum spatial overlap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in favor of the small values of ΔEST. Among the molecules studied, the one in which dihydrophenazine acts as the donor has the lowest value of ΔEST. All designed molecules are good electron transporters. The non-linear optical properties of the molecules are also examined.
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A duty ratio drive prediction (DRDP) model of luminance degradation for organic light emitting diodes (OLED) microdisplay is proposed in this paper. The traditional stretched exponential decay (SED) model is not applicable for OLED driven by duty ratio. The DRDP model introduces the duty ratio as the variables affecting the lifetime of OLED. By fitting the undetermined coefficients with the measured luminance data, the quantitative relationships among the initial luminance, duty ratio, and OLED lifetime are obtained. Meanwhile, the model quantifies the phenomenon of spontaneous luminance recovery, which occurs when OLED switches from bright to dark. Finally, the DRDP model is used to compensate the luminance degradation of OLED driven by duty ratio. The experimental results show that the average prediction accuracy of DRDP model for white, red, green, and blue (W/R/G/B) OLED degradation trend is 0.9623. The average prediction accuracy of W/R/G/B OLED lifetime is 0.6119, which is greater than that of SED model. The lifetime is extended by 89.83% after compensation.
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SilícioRESUMO
An efficient access to the novel 5-(aryl)amino-1,2,3-triazole-containing 2,1,3-benzothiadiazole derivatives has been developed. The method is based on 1,3-dipolar azide-nitrile cycloaddition followed by Buchwald-Hartwig cross-coupling to afford the corresponding N-aryl and N,N-diaryl substituted 5-amino-1,2,3-triazolyl 2,1,3-benzothiadiazoles under NHC-Pd catalysis. The one-pot diarylative Pd-catalyzed heterocyclization opens the straightforward route to triazole-linked carbazole-benzothiadiazole D-A systems. The optical and electrochemical properties of the compound obtained were investigated to estimate their potential application as emissive layers in OLED devises. The quantum yield of photoluminescence (PLQY) of the synthesized D-A derivatives depends to a large extent on electron-donating strengths of donor (D) component, reaching in some cases the values closed to 100%. Based on the most photoactive derivative and wide bandgap host material mCP, a light-emitting layer of OLED was made. The device showed a maximum brightness of 8000 cd/m2 at an applied voltage of 18 V. The maximum current efficiency of the device reaches a value of 3.29 cd/A.
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This review focuses on optical properties of compounds in which at least one phosphonate group is directly attached to a heteroaromatic ring. Additionally, the synthesis and other applications of these compounds are addressed in this work. The influence of the phosphonate substituent on the properties of the described compounds is discussed and compared with other non-phosphorus substituents, with particular attention given to photophysical properties, such as UV-Vis absorption and emission, fluorescence quantum yield and fluorescence lifetime. Considering the presence of heteroatom, the collected material was divided into two parts, and a review of the literature of the last thirty years on heteroaryl phosphonates containing sulfur and nitrogen atoms in the aromatic ring was conducted.
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Over the past few decades, organic light-emitting diodes (OLEDs) find applications in smartphones, televisions, and the automotive sector. However, this technology is still not perfect, and its application for lighting purposes has been slow. For further development of the OLEDs, we designed twisted donor-acceptor-type electroactive bipolar derivatives using benzophenone and bicarbazole as building blocks. Derivatives were synthesized through the reaction of 4-fluorobenzophenone with various mono-alkylated 3,3'-bicarbazoles. We have provided a comprehensive structural characterization of these compounds. The new materials are amorphous and exhibit suitable glass transition temperatures ranging from 57 to 102 °C. They also demonstrate high thermal stability, with decomposition temperatures reaching 400 °C. The developed compounds exhibit elevated photoluminescence quantum yields (PLQY) of up to 75.5% and favourable HOMO-LUMO levels, along with suitable triplet-singlet state energy values. Due to their good solubility and suitable film-forming properties, all the compounds were evaluated as blue TADF emitters dispersed in commercial 4,4'-bis(N-carbazolyl)-1,10-biphenyl (CBP) host material and used for the formation of emissive layer of organic light-emitting diodes (OLEDs) in concentration-dependent experiments. Out of these experiments, the OLED with 15 wt% of the emitting derivative 4-(9'-{2-ethylhexyl}-[3,3']-bicarbazol-9-yl)benzophenone exhibited superior performance. It attained a maximum brightness of 3581 cd/m2, a current efficacy of 5.7 cd/A, a power efficacy of 4.1 lm/W, and an external quantum efficacy of 2.7%.
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Efficient ultraviolet (UV) electroluminescent materials remain a great challenge, since short peak wavelength <400â nm and narrow full width at half maximum (FWHM) <50â nm are simultaneously required. In this sense, multi-resonance (MR) thermally activated delayed fluorescence (TADF) emitters featuring narrow-band emissions hold the promise for UV applications. Herein, a novel MR-TADF skeleton featuring carbazole-phosphine oxide (P=O) fused aromatics is developed to construct the first two UV MR emitters named CzP2PO and tBCzP2PO. In addition to synergistic resonance effects of P=O and N atom, sp3 -hybrid P atom renders the curved polycyclic planes of CzP2PO and tBCzP2PO, giving rise to their narrowband UV emissions with peak wavelengths <390â nm and FWHM<35â nm. Besides configuration quasi-planarization for radiation enhancement and quenching suppression, P=O moiety further enhances singlet-triplet coupling to facilitate reverse intersystem crossing, resulting in the state-of-the-art photoluminescence quantum yield of 62 % in tBCzP2PO doped films. As consequence, tBCzP2PO endowed its UV organic light-emitting diodes with the peak at 382â nm and FWHM of 32â nm, and especially the record-high external quantum efficiency (EQE) of 15.1 % among all kinds of UV devices. Our results demonstrate great potential of P=O based MR emitters in practical applications including optoelectronics, biology and medicine science.
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Currently, much research effort has been devoted to improving the exciton utilization efficiency and narrowing the emission spectra of ultraviolet (UV) fluorophores for organic light-emitting diode (OLED) applications, while almost no attention has been paid to optimizing their light out-coupling efficiency. Here, we developed a linear donor-acceptor-donor (D-A-D) triad, namely CDFDB, which possesses high-lying reverse intersystem crossing (hRISC) property. Thanks to its integrated narrowband UV photoluminescence (PL) (λPL: 397â nm; FWHM: 48â nm), moderate PL quantum yield (ÏPL: 72 %, Tol), good triplet hot exciton (HE) conversion capability, and large horizontal dipole ratio (Θ//: 92 %), the OLEDs based on CDFDB not only can emit UV electroluminescence with relatively good color purity (λEL: 398â nm; CIEx,y: 0.161, 0.040), but also show a record maximum external quantum efficiency (EQEmax) of 12.0 %. This study highlights the important role of horizontal dipole orientation engineering in the molecular design of HE UV-OLED fluorophores.
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Two new pyrimidine-based iridium complexes with triphenylamine and tetraphenylsilane, namely (TPAPr)2 IrAcac and (TPSPr)2 IrAcac, were fully synthesized and characterized. Both of the targeted iridium complexes exhibit excellent thermal stability and high photoluminescence quantum yields. Compared to (TPAPr)2 IrAcac, (TPSPr)2 IrAcac achieved its highest PLQY and current efficiency (CE) at higher dopant concentration probably because of its bulky tetraphenylsilane group, which can effectively suppress the concentration quenching. However, according to DFT studies, (TPSPr)2 IrAcac shows faster non-radiative transitions due to the presence of more excited-state distortions than (TPAPr)2 IrAcac. As a result, Green phosphorescent polymer light-emitting diodes (PLEDs) containing (TPAPr)2 IrAcac and (TPSPr)2 IrAcac as dopants exhibit exceptional device performance with peak CE values of 38.24 and 36.06â cd A-1 , respectively. (TPAPr)2 IrAcac exhibited a superior efficiency than (TPSPr)2 IrAcac because of its high Φp , low RMSD value, and efficient energy transfer from the host to the guest. More importantly, the PLEDs based on (TPAPr)2 IrAcac and (TPSPr)2 IrAcac show stable phosphorescent emission with Commission Internationale de L'Eclairage (CIE) coordinates of (0.313, 0.497) and (0.299, 0.483), respectively. This work points out a viable method for creating phosphorescent iridium complexes based on pyrimidine for high-efficiency organic light-emitting diodes (OLEDs).
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Tuning the photophysical properties of π-conjugated oligomers by functionalization of skeleton, to achieve an optically and electronically advantageous building block for organic semiconductor materials is a vital yet challenging task. In this work, a series of structurally well-defined polyaryl-functionalized α-oligofurans, in which aryl groups are introduced precisely into each of the furan units, are rapidly and efficiently synthesized by de novo metal-free synthesis of α-bi(arylfuran) monomers for the first time. This new synthetic strategy nicely circumvents the cumbersome substituent introduction process in the later stage by the preinstallation of the desired aryl groups in the starting material. The characterization of α-oligo(arylfuran)s demonstrates that photoelectric properties of coplanar α-oligo(arylfuran)s can be tuned through varying aryl groups with different electrical properties. These novel α-oligo(arylfuran)s have good hole transport capacity and can function as hole-transporting layers in organic light-emitting diodes, which is indicative of significant breakthrough in the application of α-oligofurans materials in OLEDs. And our findings offer an avenue for the ingenious use of α-oligo(arylfuran)s as p-type organic semiconductors for OLEDs.
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We report the synthesis and late-stage diversification of a new class of hetero-buckybowl, BN-embedded dibenzocorannulenes (B2 N2 -DBCs). The synthesis is achieved via one-shot halogenative borylation, comprising the nitrogen-directed haloboration of alkyne and an intramolecular bora-Friedel-Crafts reaction, which provides BN-embedded dibenzocorannulene possessing two bromo substituents (B2 N2 -DBC-Br). B2 N2 -DBC-Br undergoes diversification via coupling reactions to provide a variety of arylated derivatives (B2 N2 -DBC-R), exhibiting strong blue fluorescence. An organic light-emitting diode (OLED) employing one of the derivatives as an emitter exhibited a high external quantum efficiency of 6.6 % and long operational lifetime of 907â h at an initial luminance of 1000â cd m-2 , indicating the significant potential for the development of efficient and stable hetero-buckybowl-based OLED materials.
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Alcinos , Nitrogênio , FluorescênciaRESUMO
Four A-π-D-π-A type small organic molecules with 1,8-naphthalimide motifs were successfully synthesised. The designed compounds are built of two 1,8-naphthalimide units linked via ethynyl π-linkages with selected functionalised donor motifs i. e. 2,2'-bithiophene, fluorene, phenothiazine and carbazole derivative. The synthesis based on Sonogashira cross-coupling allowed us to obtain the presented dyes with good yields. The resulting symmetrical small molecules' optical, electrochemical and thermal properties were thoroughly investigated, and their potential applicability for the OLED devices was demonstrated. In addition, the relationship between molecular structure and properties was considered by employing experimental and theoretical studies. As a result of using various donor groups, it was possible to achieve efficient electroluminescence in the range from green (DEV4) to orange-red light (DEV3) with a maximum luminance of 3 820â cd/m2 for DEV4. Upon the insertion of an acetylene linker to the designed molecules, the free rotation of D and A fragments, and hence the effective π-electron communication within the entire molecule, is possible, which was confirmed by DFT studies. The obtained dyes are characterised by high thermal stability, reversible oxidation-reduction process, satisfactory optoelectronic properties and good solubility in organic solvents, which is advisable for the application in small molecular organic light-emitting diodes (SM-OLEDs) technology.
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Coinage metal (gold, silver, and copper) complexes are attractive candidates to substitute the widely studied noble metal complexes, such as, iridium(III) and platinum(II), as luminescent materials in organic light-emitting diodes (OLEDs). However, the development of coinage metal complexes exhibiting high emission quantum yields and short exciton lifetimes is still a formidable challenge. In the past few years, coinage metal complexes featuring a carbene-metal-amide (CMA) motif have emerged as a new class of luminescent materials in OLEDs. Thanks to the coinage metal-bridged linear geometry, coplanar conformation, and the formation of excited states with dominant ligand-to-ligand charge transfer character and reduced metal d-orbital participation, most CMA complexes have high radiative rates via thermally activated delayed fluorescence. Currently, the family of CMA complexes have rapidly evolved and remarkable progresses in CMA-based OLEDs have been made. Here, a Concept article on CMA complexes is presented, with a focus on molecular design principles, the correlation between molecular structure/conformation and optoelectronic properties, as well as OLED performance. The future prospects of CMA complexes are also discussed.
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Although the effect of the electron blocking layer (EBL) material, deoxyribonucleic acid (DNA), on the electroluminescence (EL) performance of organic light-emitting diodes (OLEDs) has been studied, the process of DNA regulation of exciton recombination region within the device is still unclear. Herein, devices with and without EBL were fabricated using different DNA spin-coating speeds, and the photoelectric performance of device were measured. By using DNA compounded with cetyltrimethyl ammonium (CTMA) as the EBL and hole buffer layer, so-called BioLEDs. The DNA-based green Alq3BioLEDs achieve higher luminance (39 000 cd m-2) and higher current efficiency (8.4 cd A-1), which are increased by 49% and 54%, respectively, compared to the reference OLEDs without the addition of DNA. Similarly, the maximum luminance and efficiency of yellow Rubrene BioLEDs is increased by 64% (from 12 120 to 19 820 cd m-2) and 74% (from 1.36 to 2.36 cd A-1), the luminance and efficiency of blue TCTA BioLEDs is increased by 101% and 245%. Specifically, we found that as the thickness of DNA-CTMA increases, the exciton recombination region moves towards the interface between the emitting layer (EML) and the hole transport layer (HTL). By better confining excitons within the EML, the current efficiency of the BioLEDs is effectively improved. Accordingly, we provide a possible idea for achieve high performance DNA-based BioLEDs by adding DNA-CTMA EBL and hole buffer layers. Meanwhile, as the DNA thickness increases, the exciton recombination region moves towards the EML/HTL interface, thereby enhancing the efficiency of the DNA-based BioLEDs.
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Thermally activated delayed fluorescent emitters based on carbazole donor, benzonitrile acceptor with the linkers biphenyl, bipyridine and naphthalene are investigated using the density functional theoretical method. The molecule in which bipyridine acts as the linker with the least ΔEST is further selected for the designing of a series of D-L-A framework TADF molecules. Remarkably, the ΔEST is decreased successively by attaching the additional cyano groups at the acceptor site which is further reduced when the electron donating methoxy groups are attached at the donor site. To know the effect of substituents on ΔEST, the acceptor moiety of the D-L-A framework is modified with -F, -Cl and -CF3 substituents. The studies showed a relatively less decrement in the value of ΔEST compared to the cyano substituted molecules. However, ΔEST significantly reduced further on attaching methoxy groups at the donor site.
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Luminescent lanthanide complexes exhibiting chiroptical properties are attracting attention for their application in chiral optoelectronics and photonics, thanks to their unique optical properties, allied to intraconfigurational f-f transitions, which are generally electric-dipole-forbidden and can be magnetic dipole-allowed, which in an appropriate environment can lead to high dissymmetry factors and strong luminescence, in the presence of an antenna ligand. However, because luminescence and chiroptical activity are governed by different selection rules, their successful application in commonly used technologies is still an expectation. Recently, we showed that europium complexes bearing ß-diketonates acting as luminescence sensitizers, and chiral bis(oxazolinyl) pyridine derivatives as the chirality inducer, reasonably perform in circularly polarized (CP) organic light-emitting devices (OLEDs). Indeed, europium ß-diketonate complexes are an interesting molecular starting point, given their strong luminescence and their established use in conventional (i.e., nonpolarized) OLEDs. In this context, it is interesting to investigate in detail the impact of the ancillary chiral ligand on complex emission properties and the performances of corresponding CP-OLEDs. Here we show that, by incorporating the chiral compound as emitter in the architecture of solution processed electroluminescent devices, CP emission is retained, and the efficiency of the device is comparable to reference unpolarized OLED. The observed remarkable dissymmetry values strengthen the position of chiral lanthanide-OLEDs as CP-emitting devices.