Forthcoming hyperfluorescence display technology: relevant factors to achieve high-performance stable organic light emitting diodes

Rational Design of Color-Pure Blue Organic Emitters by Poly-Heteroaromatic Omni-Delocalization

Current research on organic light emitters which utilize multiple resonance-induced thermally activated delayed fluorescence (MR-TADF) materials is gaining significant interest because of the materials' ability to efficiently generate color-pure blue emission. However, the underlying reasons for high color purity remain unclear. It is shown here that these emitters share a common electronic basis, which is deduced from resonance structure considerations following Clar's rule, and which is termed as "poly-heteroaromatic omni-delocalization" (PHOD). The simple and clear design rules derived from the PHOD concept allow extending the known chemical space by new structural motifs. Based on PHOD, a set of novel high-efficiency color-pure emitters with brilliant deep-blue hue is specifically designed.

Structural Optimization of BODIPY Derivatives: Achieving Stable and Long-Lived Green Emission in Hyperfluorescent OLEDs

Boron dipyrromethene (BODIPY) derivatives are widely studied as terminal emitters in organic light-emitting diodes (OLED) due to their narrow emission and high photoluminescence quantum yield (PLQY). However, the strategy for precisely tuning their emission toward a high color purity is still challenging. Herein, we developed a new design strategy to regulate the emission of BODIPY derivatives by modifying the electronic and steric dominance using functionalities, such as nitrile, pentafluorophenyl, diethyl, and monobenzyl. These rational modifications yielded a series of four novel green BODIPY emitters, namely, tPN-BODIPY, tPPP-BODIPY, tPBn-BODIPY, and tPEN-BODIPY, each benefited with a tuned emissions range of 517 to 542 nm with a narrow fwhm of 25 nm and high photoluminescence quantum yield up to 96%. Among these synthesized BODIPYs, an unsymmetrical tPBn-BODIPY was chosen as a final dopant (FD) to explore its application in OLED devices. The fabricated TADF sensitized fluorescence-OLED (TSF-OLED) exhibits a narrow band pure green emission at 531 nm with corresponding CIE coordinates of (x, y) = (0.27, 0.68) and a maximum external quantum efficiency (EQE) of 20%. Furthermore, the TSF-OLED displayed an exceptionally prolonged device operational lifetime (LT90) of 210 h at an initial luminescence of 3000 cd m-2.

Combined DFT and QM/MM Modeling on Multifunctional TADF Sensitizers and Hot-Exciton Emitters via Carborane Triads for Blue Hyperfluorescent OLEDs

The scarcity of novel luminogens significantly impedes the advancement of TADF sensitizers and hot exciton emitters, attracting considerable attention for their potential to enhance energy conversion efficiencies in hyperfluorescent OLEDs. In this study, a systematic investigation is employed to design and develop multifunctional materials based on carborane cores through DFT and TD-DFT methods. In pursuit of this objective, 45 carborane triad-type molecules were systematically designed using four donors and two acceptor units. Electronic structure calculations revealed that (i) the singlet, triplet, ΔEST, and SOC values exhibit an increased trend as the carborane core shifts from ortho to meta to para, while an increase in donor strength on the core leads to a decrease in these values. (ii) Moreover, there is a decrease in reorganization energies, absorption wavelengths, ISC, and RISC rates as the carborane switches from ortho to meta to para while witnessing an increase in donor strength. The QM/MM study reveals that para carborane's restricted intramolecular motions improve its solid-state aggregation over ortho carborane and solution phases. Interestingly, carborane triads featuring P-DMB and P-BODIPY acceptor units satisfy the desired criteria for multifunctional TADF sensitizers and hot exciton emitters, respectively.

Bis-tridentate Ir(III) Phosphors and Blue Hyperphosphorescence with Suppressed Efficiency Roll-Off at High Brightness

Narrowband blue emitters are indispensable in achieving ultrahigh-definition OLED displays that satisfy the stringent BT 2020 standard. Hereby, a series of bis-tridentate Ir(III) complexes bearing electron-deficient imidazo[4,5-b]pyridin-2-ylidene carbene coordination fragments and 2,6-diaryloxy pyridine ancillary groups were designed and synthesized. They exhibited deep blue emission with quantum yields of up to 89% and a radiative lifetime of 0.71 μs in the DPEPO host matrix, indicating both the high efficiency and excellent energy transfer process from the host to dopant. The OLED based on Irtb1 showed an emission at 468 nm with a maximum external quantum efficiency (EQE) of 22.7%. Moreover, the hyper-OLED with Irtb1 as a sensitizer for transferring energy to terminal emitter v-DABNA exhibited a narrowband blue emission at 472 nm and full width at half-maximum (FWHM) of 24 nm, a maximum EQE of 23.5%, and EQEs of 19.7, 16.1, and 12.9% at a practical brightness of 100, 1000, and 5000 cd/m2, respectively.

Sulfur Oxidation State and Substituents Influenced Multifunctional Organic Luminophores in BTP Core for OLEDs: A Computational Study on RTP, TADF Emitter and Sensitizer

The exploration of triplet excitons in thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) molecules has become a subject of significant attention and interest in recent studies. This study employed density functional theory (DFT) and time-dependent DFT theoretical methods to delve into the intricate relationship between the molecular structure and properties of molecules designed with the oxidation of sulfur atoms (S, SO, and SO2) in benzothiazinophenothiazine (BTP) core units. The calculations revealed that as the oxidation state of the sulfur atom increased, the BTP derivatives exhibited elevated ionization potentials (IPs), electron affinities (EAs), and triplet energies (ET), accompanied by reduced reorganization energies (λ), singlet energies (ES), and a S1-T1 energy gap (ΔEST). Additionally, the decrease in the exchange energy prompts a shift in the excited-state properties of molecules, transitioning them from hybridized local and charge transfer (HLCT) to charge transfer (CT) in the S1 state while maintaining their HLCT character in the T1 state. The sulfur oxidation process systematically decreases spin-orbit coupling magnitudes in the S1-T1 and T1-S0 pathways while increasing the KRISC rate, signifying a reduced propensity for phosphorescence radiative decay in oxidized molecules. Thorough investigations have explored the screening effect and orbital mixing of lone pair electrons in sulfur atoms, satisfying the desired criteria for a multifunctional RTP, TADF emitter and sensitizer.

Neoteric Advances in Oxygen Bridged Triaryl Boron-based Delayed Fluorescent Materials for Organic Light Emitting Diodes

Since their first demonstration, thermally activated delayed fluorescence (TADF) materials have been emerged as the most promising emitters because of their promising applications in optoelectronics, typified by organic light-emitting diodes (OLEDs). In which, the rigid oxygen bridged boron acceptor-featured (DOBNA) emitters have gained tremendous impetus for OLEDs, which is ascribed to their excellent external quantum efficiency (EQE). However, these materials often displayed severe efficiency roll-off and poor operational stability. Therefore, there needs to be a comprehensive understanding of the aspect of the molecular design and structure-property relationship. To the best of our knowledge, there is no detailed review on the structure-function outlook of DOBNA-based emitters emphasizing the effect of the nature of donor units, their number density, and substitution pattern on the physicochemical properties, excited state dynamics and OLED performance were reported. To fill this gap, herein we presented the recent advancements in DOBNA-based acceptor featured TADF materials by classifying them into several subgroups based on the molecular design i. e. donor-acceptor (D-A), D-A-D, A-D-A, and multi-resonant TADF (MR-TADF) emitters. The detailed design concepts, along with their respective physicochemical and OLED performances were summarized. Finally, the prospective of this class of materials in forthcoming OLED displays is also discussed.

Fluorescent homooxacalixarenes: recent applications in supramolecular systems

This review covers recent advances (from 2006 to date) in supramolecular systems based on fluorescent homooxacalixarenes, namely hexahomotrioxacalix[3]arenes, dihomooxacalix[4]arenes and tetrahomodioxacalix[4]arenes, focusing on fluorescence sensing using their intrinsic fluorescence (built-in mesitol-like groups) or the extrinsic fluorescence of organic fluorophores, either covalently linked to the calixarenes or forming supramolecular complexes with them. Sensing applications of ions, ion pairs and neutral molecules are discussed, as well as the potential measurement of temperature based on thermally activated delayed fluorescence.