Hybridized Local And Charge-transfer Research Articles

An efficient solution-processable hybridized local and charge-transfer (HLCT)-based deep-red fluorescent emitter for simple structured non-doped OLED

The development of highly efficient deep-red fluorescent emitters is still a challenging task due to their intrinsic low bandgap characteristics resulting in low fluorescence emission in solid-state. Moreover, most of efficient deep-red organic light-emitting diodes (OLEDs) have complex device structures and are fabricated by high-cost vacuum deposition techniques. Herein, a novel solution-processable hybridized local and charge-transfer (HLCT) deep-red fluorescent molecule, TPA-NZF, is designed and synthesized as an emitter for low-cost and simple-structured OLEDs. TPA-NZF comprises a strong electron-deficient naphthothiadiazole (NZ) functionalized with triphenylamine (TPA) as a donor and dioctylfluorene as a solubilizing moiety. The photophysical results and theoretical calculations reveal a strong donor-acceptor feature and deep-red fluorescent emission with a solid-state photoluminescence quantum yield as high as 44%, decent hole-transporting mobility, good film morphology, and thermal and electrochemical stabilities. TPA-NZF is successfully fabricated as a solution-processed non-doped emitter in simple structured OLEDs. The device shows excellent electroluminescence (EL) performance (maximum external quantum efficiency (EQEmax) of 3.59%) and a deep-red emission with CIE coordinates of (0.66, 0.33).

Highly efficient hybridized local and Charge-transfer (HLCT) Deep-blue electroluminescence with excellent molecular horizontal orientation

Efficient deep-blue emitters with nice color purity are fundamental in organic light-emitting diode (OLED) applications. Herein, we report two phenanthroimidazole (PPI) derivative deep-blue emitters (DP, SP) with hybrid local and charge-transfer (HLCT) properties of high photoluminescence quantum yield (PLQY) and nice color purity. More importantly, the horizontal dipole orientation (Θ//) of them are both superior to the isotropic emitters (66.7%), especially the Θ// of SP is 89.5%, which can greatly improve its OLED performance. As a result, non-doped OLED of SP exhibits deep-blue emission with Commission Internationale de lEclairage (CIE) coordinate of (0.158, 0.068) and maximum external quantum efficiency (EQEmax) of 11.3%, which is nearly twice that of DP and is one of the best results among the non-delayed, non-doped deep-blue fluorescent OLEDs. Furthermore, SP-based doped OLED displays an excellent performance of near ultraviolet (NUV) emission at 406 nm with CIE coordinate of (0.157, 0.046) and EQEmax of 7.5%, which is also a competitive result in the materials with comparable NUV OLED applications.

Efficient Ultraviolet Organic Light-Emitting Diodes with a CIEy of 0.04 and Negligible-Efficiency Roll-Off.

Organic light-emitting diodes (OLEDs) with ultraviolet (UV) emission (λEL ≤ 400 nm) have attracted special attention in commercial and civil fields owing to their special functions. Nevertheless, the lack of high-quality ultraviolet emitters restricts the practical application of UV OLEDs. Herein, a novel organic molecule with desirable UV emission, 2Na-CzCN, is developed for UV OLEDs. Theoretical investigation indicates that it is equipped with hybridized local and charge-transfer (HLCT) characteristics, which is in favor of the high-lying reverse intersystem crossing (RISC) process, thus remarkably boosting the exciton utilization in electroluminescence (EL). Significantly, the nondoped device derived from the 2Na-CzCN emitter exhibits an EL emission peak of 398 nm with a maximum external quantum efficiency (EQE) of 5.92%, which represents the record-high result among nondoped UV OLEDs. The doped UV OLED of 2Na-CzCN radiates robust UV emission at a peak of 392 nm with a maximum EQE of 6.15%. Coupled with the narrow full width at half-maximum (FWHM) of the EL spectra, desirable color purities with Commission Internationale de l'Eclairage (CIE) coordinates of (0.15, 0.06) and (0.16, 0.04) for nondoped and doped OLEDs are presented, respectively. Additionally, the potential of 2Na-CzCN adopted as the host material is demonstrated with phosphorescent OLEDs (PhOLEDs), and all of the devices show good EL performances with low-efficiency roll-offs. An orange PhOLED with 2Na-CzCN acquires a maximum current and external quantum efficiency of 84.9 cd A-1 and 25.3%, respectively. These findings may pave an avenue for the development of high-performance UV emitters.

Efficient deep blue (CIE ∼0.08) fluorophore-based benzimidazole with hybridized local and charge transfer (HLCT) excited state for OLEDs

Development of efficient deep blue fluorophore with Commission Internationale de l’Eclairage (CIE)y value <0.1 is of great importance for display technology. Herein, we designed and synthesized a thermally stable deep blue emissive material 3-(2-(4′′-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1′:4′,1″-terphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)benzonitrile (MCNPIBI) by integrating moderate donor and acceptor, namely, phenanthroimidazole (PI) and benzimidazole with cyanophenyl (-CN) group at N1 position of the PI to tune the CT component in the excited states. The systematic theoretical and photophysical study reveals the MCNPIBI with hybridized local and charge transfer (HLCT) excited states. Time-dependent density functional theory (TD-DFT) calculation suggests that the reverse intersystem crossing (RISC) process in MCNPIBI occurs from high-lying triplet states to a singlet state. Furthermore, the synthesized deep blue emissive materials were employed as dopants in multilayer organic light emitting diode (OLED) devices, thus resulting in deep-blue electroluminescence (EL) with an emission wavelength of 447 nm and CIE coordinates of (0.15, 0.08), which are close to the standard values for blue emitters, as suggested by NTSC (0.14, 0.08). The OLED device displays a maximum current efficiency of 2.78 cd A−1, a maximum power efficiency of 1.94 lm W−1, and a maximum external quantum efficiency of 3.69%, respectively. In addition, the OLED device has a low turn in voltage of 3.8 V.

An efficient solution-processable non-doped hybridized local and charge-transfer (HLCT) emitter for a simplified organic light-emitting diode

A solution-processable HLCT fluorescent molecule realizes a highly efficient non-doped OLED with a high brightness of 30 800 cd m−2, a maximum external quantum efficiency (EQEmax) of 6.74% and a maximum current efficiency (CEmax) of 14.38 cd A−1.

Photophysical properties of push-π-pull type chromophores of aryl-substituted bipyridines in different solvents

Photophysical studies of 4′-methyl-2,2′-bipyridine derivatized with the polycyclic aromatic hydrocarbons (PAHs) anthracene (mbpy-anth), naphthalene (mbpy-naph), and pyrene (mbpy-pyr) were acquired in different solvents. While the absorption spectra were not affected by the solvent nature, the emission ones showed red shifts with increase polarity consistent with an intramolecular charge-transfer (ICT) character. Theoretical calculations found a dominant “Hole” → “Particle” contribution for the first five transitions involving local excited-state (LE) and ICT transitions, with the latter being dominant at higher wavelengths (S0 → 1CT). The fluorescence solvatochromic data suggested a hybridized local and charge transfer (HLCT) state for the mbpy-R compounds with the CT contribution prevailing in high polar solvents; a result that was corroborated by the monoexponential decay lifetimes. The Stokes shifts difference between heptane and dimethylsulphoxide, the most and least polar solvents used in this work, was calculated as 1315, 2969, and 808 cm−1 for mbpy-naph, mbpy-anth, and mbpy-pyr, respectively. The increase of the solvent polarity results in a red shift and a broadening of the emission and excitation bands for mbpy-anth and mbpy-naph with the spectra of the latter being the most affected. For mbpy-pyr, on the contrary, the emission spectra were narrower than the excitation ones indicating the La transitions lie at lower energy than the Lb. For this species, the results indicated an effective mixing of LE and CT states in the moderately polar solvents being in accordance with the observed single exponential decay which is likely related to one hybridized state.

Understanding and Tailoring Excited State Properties in Solution-Processable Oligo(p-phenyleneethynylene)s: Highly Fluorescent Hybridized Local and Charge Transfer Character via Experiment and Theory.

Rod-shaped oligo(p-phenyleneethynylene) (OPE) offers an attractive π-framework for the development of solution-processable highly fluorescent molecules having tunable hybridized local and charge transfer (HLCT) excited states and (reverse) intersystem crossing ((R)ISC) channels. Herein, an HLCT oligo(p-phenyleneethynylene) library was studied for the first time in the literature in detail systematically via experiment and theory. The design, synthesis, and full characterization of a new highly fluorescent (ΦPL-solution ∼ 1) sky blue emissive 4',4‴-((2,5-bis((2-ethylhexyl)oxy)-1,4-phenylene)bis(ethyne-2,1-diyl))bis(N,N-diphenyl-[1,1'-biphenyl]-4-amine) (2EHO-TPA-PE) was also reported. The new molecule consists of a D'-Ar-π-D-π-Ar-D' molecular architecture with an extended π-spacer and no acceptor unit, and detailed structural, physicochemical, single-crystal, and optoelectronic characterizations were performed. A high solid-state quantum efficiency (ΦPL-solidstate ∼ 0.8) was achieved as a result of suppressed exciton-phonon/vibronic couplings (no π-π interactions and multiple (14 per dimeric form) strong C-H···π interactions). Strong solution-phase/solid-state dipole-dependent tunable excited state behavior (local excited (LE) → HLCT → charge transfer (CT)) and decay dynamics covering a wide spectral region were demonstrated, and the CT state was observed to be highly fluorescent despite extremely large Stokes shift (∼130 nm)/fwhm (∼125 nm) and significant charge separation (0.75 charge·nm). Employing the Lippert-Mataga model, along with detailed photophysical studies and TDDFT calculations, key relationships between molecular design-electronic structure-exciton characteristics were elucidated with regards to HLCT and hot exciton channel formations. The interstate coupling between CT and LE states and the interplay of this coupling with respect to medium polarity were explored. A key relationship between excited-state symmetry breaking process and the formation of HLCT state was discussed for TPA-ended rod-shaped OPE π-systems. (R)ISC-related delayed fluorescence (τ ∼ 2-6 ns) processes were evident following the prompt decays (∼0.4-0.9 ns) both in the solution and in the solid-state. As a unique observation, the delayed fluorescence could be tuned and facilitated via small dielectric changes in the medium. Our results and the molecular engineering perspectives presented in this study may provide unique insights into the structural and electronic factors governing tunable excited state and hot-exciton channel formations in OPEs for (un)conventional solution-processed luminescence applications.

Constructing Highly Efficient Blue OLEDs with External Quantum Efficiencies up to 7.5 % Based on Anthracene Derivatives

Acquiring desirable device performance with deep-blue color purity that fulfills practical application requirements is still a challenge. Bipolar fluorescent emitters with hybrid local and charge transfer (HLCT) state may serve to address this issue. Herein, by inserting anthracene core in the deep-blue building blocks, the authors successfully developed two highly twisted D-π-A fluorescent emitters, ICz-An-PPI and IP-An-PPI, featuring different acceptor groups. Both exhibited superb thermal stabilities, high photo luminescent quantum yields and excellent bipolar transport capabilities. The non-doped OLEDs using ICz-An-PPI and IP-An-PPI as the emitting layers showed efficient blue emission with an external quantum efficiency (EQEmax ) of 4.32 % and 5.41 %, and the CIE coordinates of (0.147, 0.180) and (0.149, 0.150), respectively. In addition, the deep blue doped device based on ICz-An-PPI was achieved with an excellent CEmax of 5.83 cd A-1 , EQEmax of 4.6 % and the CIE coordinate of (0.148, 0.078), which is extremely close to the National Television Standards Committee (NTSC) standard. Particularly, IP-An-PPI-based doped device had better performance, with an EQEmax of 7.51 % and the CIE coordinate of (0.150, 0.118), which was very impressive among the recently reported deep-blue OLEDs with the CIEy <0.12. Such high performance may be attributed to the hot exciton HLCT mechanism via T7 to S2 . Our work may provide a new approach for designing high-efficiency deep-blue materials.

Effect of hybridized local and charge transfer molecules rotation in excited state on exciton utilization

The fluorescent molecules utilizing hybridized local and charge-transfer (HLCT) state as potential organic light-emitting diodes materials attract extensive attention due to their high exciton utilization. In this work, we have performed the density functional theory method on three HLCT-state molecules to investigate their excited-state potential energy surface (PES). The calculated results indicate the T1 and T2 energy gap is quite large, and the T2 is very close to S1 in the energy level. The large gap is beneficial for inhibiting the internal conversion between T1 and T2, and quite closed S1 and T2 energies are favor for activating the T2 → S1 reverse intersystem crossing path. However, considering the singlet excited-state PES by twisting the triphenylamine (TPA) or diphenylamine (PA) group, it can be found that the TPA or PA group almost has no influence on T1 and T2 energy levels. However, the plots of S1 PES display two kinds of results that the S1 emissive state is dominated by charge-transfer (CT) or HLCT state. The CT emission state formation would decrease the S1 energy level, enlarge the S1 and T2 gap, and impair the triplet exciton utilization. Therefore, understanding the relationship between the S1 PES and molecular structures is important for designing high-performance luminescent materials utilizing HLCT state.

Efficiency Breakthrough of Fluorescence OLEDs by the Strategic Management of “Hot Excitons” at Highly Lying Excitation Triplet Energy Levels

AbstractAggregation‐induced emission (AIE) and hybridized local and charge‐transfer (HLCT) materials are two kinds of promising electroluminescence systems for the fabrication of high‐efficiency organic light‐emitting diodes (OLEDs) by harnessing “hot excitons” at the high‐lying triplet exciton states (Tn, n ≥ 2). Nonetheless, the efficiency of the resulting OLEDs did not meet expectations due to the possible loss of Tn→Tn−1. Herein, experimental results and theoretical calculations demonstrate the “hot exciton” process between the high‐lying triplet state T3 and the lowest excited singlet state S1 in an AIE material 4⁗‐(diphenylamino)‐2″,5″‐diphenyl‐[1,1″:4′,1″:4″,1′″:4′″,1⁗‐quinquephenyl]‐4‐carbonitrile (TPB‐PAPC) and it is found that the Förster resonance energy transfer (FRET) between two molecules can facilitate the “hot exciton” process and inhibit the T3→T2 loss by doping a blue fluorescent emitter in TPB‐PAPC. Finally, the doped TPB‐PAPC blue OLEDs achieve a maximum external quantum efficiency (EQEmax) of 9.0% with a small efficiency roll‐off. Furthermore, doping the blue fluorescent emitter in a HLCT material 2‐(4‐(10‐(3‐(9H‐carbazol‐9‐yl)phenyl)anthracen‐9‐yl)phenyl)‐1‐phenyl‐1H‐phenanthro[9,10‐d] imidazole (PAC) is used as the emission layer, and the resulting blue OLEDs exhibit an EQEmax of 17.4%, realizing the efficiency breakthrough of blue fluorescence OLEDs. This work establishes a physical insight in the design of high‐performance “hot exciton” molecules and the fabrication of high‐performance blue fluorescence OLEDs.

High‐Performance Ultraviolet Organic Light‐Emitting Diode Enabled by High‐Lying Reverse Intersystem Crossing

AbstractUltraviolet (UV) organic emitters that can open up applications for future organic light‐emitting diodes (OLEDs) are of great value but rarely developed. Here, we report a high‐quality UV emitter with hybridized local and charge‐transfer (HLCT) excited state and its application in UV OLEDs. The UV emitter, 2BuCz‐CNCz, shows the features of low‐lying locally excited (LE) emissive state and high‐lying reverse intersystem crossing (hRISC) process, which helps to balance the color purity and exciton utilization of UV OLED. Consequently, the OLED based on 2BuCz‐CNCz exhibits not only a desired narrowband UV electroluminescent (EL) at 396 nm with satisfactory color purity (CIEx, y=0.161, 0.031), but also a record‐high maximum external quantum efficiency (EQE) of 10.79 % with small efficiency roll‐off. The state‐of‐the‐art device performance can inspire the design of UV emitters, and pave a way for the further development of high‐performance UV OLEDs.

Bipolar Molecules with Hybridized Local and Charge‐Transfer State for Highly Efficient Deep‐Blue Organic Light‐Emitting Diodes with EQE of 7.4% and CIEy ∼ 0.05

AbstractDonor−acceptor molecules with hybridized local and charge transfer (HLCT) excited state have been demonstrated to be an efficient strategy for achieving high performance electroluminescence by harvesting both singlet and triplet excitons. In this study, a series of bipolar D−A molecules with twisted bridge are synthesized and these chromophores exhibit good thermal, morphological and photophysical properties, electrochemical stabilities as well as HLCT excited state features. Excellent deep‐blue electroluminescence (EL) performances are achieved using CSiTPI (external quantum efficiency (EQE) of 7.1% and CIEx,y coordinates of (0.16, 0.06) in a nondoped OLED) and DSiTPI (EQE of 7.4% and CIEx,y of (0.16, 0.05) in a doped OLED) as emitters with small full width at half maxima (FWHM, 45−48 nm). Devices using DSiTPI and CSiTPI as hosts are also fabricated and all the devices show high EL performances and small efficiency roll‐offs. A green device with DSiTPI acquires maximum current, power, and EQE of 78.5 cd A−1, 72.5 lm W−1, and 20.8%. The research demonstrates that excellent deep‐blue EL performances with good color purity can be achieved using D−A emitters with highly twisted bridge in HLCT OLEDs.

A solution-processable hybridized local and charge-transfer (HLCT) phenanthroimidazole as a deep-blue emitter for efficient solution-processed non-doped electroluminescence device

Most highly efficient hybridized local and charge-transfer (HLCT)-based organic light‐emitting diodes (OLEDs) are multi-layer devices fabricated by thermal vacuum evaporation techniques, which are inappropriate for the simplified device fabrication process. However, there are only a couple of reported examples of solution-processed HLCT OLEDs, particularly deep-blue OLEDs. Herein, we design and synthesize a solution-processable HLCT emitter, CPPI, in which 1,2-diphenyl-phenanthroimidazole (PI) as an acceptor core is substituted by three 3,6-di-tert-butyl-N-phenyl-carbazole (CP) moieties as a donor and hole-transporting/solubilizing unit. The HLCT and photophysical properties are thoroughly examined by theoretical and experimental methods. CPPI exhibits HLCT characteristics with intense deep-blue color emission, high thermal and electrochemical stability, and decent hole-transporting ability. The molecule is successfully fabricated as a solution-processed non-doped emitter in organic light-emitting diodes (OLED). The solution-processed OLED retains efficient and stable deep-blue color emission (CIE coordinates of (0.157, 0.089)) with a narrow FWHM of 66 nm, an EQEmax of 3.39% and a high exciton utilization efficiency of 42.4%. Crucially, this result signifies an advance in developing a solution-processable HLCT molecule as an emitter for solution-processed non-doped OLEDs.

A Novel Deep Blue LE-Dominated HLCT Excited State Design Strategy and Material for OLED

Deep blue luminescent materials play a crucial role in the organic light-emitting diodes (OLEDs). In this work, a novel deep blue molecule based on hybridized local and charge-transfer (HLCT) excited state was reported with the emission wavelength of 423 nm. The OLED based on this material achieved high maximum external quantum efficiency (EQE) of 4% with good color purity. The results revealed that the locally-excited (LE)-dominated HLCT excited state had obvious advantages in short wavelength and narrow spectrum emission. What is more, the experimental and theoretical combination was used to describe the excited state characteristic and to understand photophysical property.

Anthracene-based emitters for highly efficient deep blue organic light-emitting diodes with narrow emission spectrum

Organic light-emitting diodes (OLEDs) are expected to support the future applications in flat-panel displays and solid-state lightings owing to their advantages of flexibility, light weight, high resolution, energy conservation, etc. Achieving efficient deep blue electroluminescence with excellent color purity (narrow emission) remains a big challenge for OLEDs. Herein, two anthracene derivatives, PIAnTPh and PyIAnTPh, with a hybridized local and charge transfer (HLCT) excited state are obtained by attaching the large periphery groups of phenanthroimidazole/pyrenoimidazole and terphenyl unit to the 9,10-positions of anthracene. The sterically asymmetric strategy can efficiently suppress the unfavorable intermolecular interactions and realize deep blue emission. The introduction of neutral terphenyl unit avoids the potential reduction of fluorescence quantum yield from strong charge transfer (CT) characteristics. More importantly, the relatively weak CT state and the rigid molecular structure can significantly reduce the vibrational motion to obtain relatively narrow emission spectra. The doped devices based on PIAnTPh and PyIAnTPh show strong deep blue electroluminescence with CIE coordinates of (0.15, 0.06) and (0.15, 0.07), high color purity, and narrow full width at half maxima (FWHM) of merely 50 and 52 nm, respectively, meeting well with the EBU standard. The EQEs are as high as 8.09% and 8.44% for PIAnTPh and PyIAnTPh, which are among the state-of-the-art deep blue OLEDs.

Donor-π-acceptor materials for robust electroluminescence performance based on hybridized local and charge-transfer state

Efficient and robust organic light-emitting diodes (OLEDs) have always been of great interest for both academia and industry. In this work, two electroluminescence donor-π-acceptor structure materials 3,6-TC and 3,6-T2C were synthesized and investigated on their excited state properties and electroluminescence performances. The non-doped and doped OLED of the two materials both exhibited high maximum external quantum efficiency (EQE) of near 5% and exciton utilizing efficiency (EUE) of over 60%. More importantly, the introduction of an extra cyano group of 3,6-T2C facilitated a fine modulation of hybridized local and charge-transfer (HLCT) excited state with a crossed dipole of CT transition and an energy favorable high-lying reverse intersystem crossing (RISC), which contributed to a more stable photoluminescence (PL) and EUE than the 3,6-TC. This work provided a novel design strategy to realize high-performance OLED device by the fine modulation in HLCT state.

Tuning the dual emission of keto/enol forms of excited-state intramolecular proton transfer (ESIPT) emitters via intramolecular charge transfer (ICT)

Herein disclosed the adjustment of the dual emission of keto and enol forms of excited-state intramolecular proton transfer (ESIPT) emitters via intramolecular charge transfer (ICT) effects. Introducing electron-donating triphenylamine (TPA) and electron-withdrawing triphenylboron (TPB) substituents into the para-position of the phenolic hydroxyl group or the side of the oxazole of 2-(2′-hydroxyphenyl)oxazole skeleton endows the resulting compounds (6a-6d) with different photophysical properties. Owing to the ICT effect from electronic donor to acceptor, introducing TPA into the side of oxazole and TPB into the para-position of phenolic hydroxyl is conducive to an enol-form emission (6a). Exchanging the two substituents, namely introducing TPB into the side of oxazole and TPA into the para-position of phenolic hydroxyl, would be beneficial to a keto-form emission (6b). Synchronously introducing two identical substituents, whether TPA or TPB, into two sides of 2-(2′-hydroxyphenyl)oxazole skeleton (6c and 6d) would lead to the dual emission of keto and enol forms due to the excited-state equilibrium of ESIPT reactions, which are further verified by DFT calculation. The organic light-emitting diode (OLED) devices with 6a and 6c as emitters were fabricated, both of which exhibit hybridized local and charge transfer (HLCT) excited-state characters with high external quantum efficiencies (EQEs) of 4.9% and 5.6%, respectively.

Efficient and stable deep-blue narrow-spectrum electroluminescence based on hybridized local and charge-transfer (HLCT) state

Two phenanthroimidazole-acridine derivatives (DPM and TDPM) were designed and synthesized for deep-blue organic light-emitting diode (OLED). Twisted combined rigid structures with hybridized local and charge-transfer (HLCT) state properties enable them to achieve excellent OLED performance. Non-doped OLEDs based on DPM and TDPM show decent deep-blue narrow-spectrum emission with Commission International de L’Éclairage (CIE) coordinates of (0.157, 0.053) and (0.158, 0.045), as well as maximum external quantum efficiency (EQEmax) of 4.0% and 2.6%, respectively. More importantly, OLEDs based on TDPM exhibit a smaller efficiency roll-off (12%) than that of DPM (35%) at high brightness (820 cd m−2 for DPM and 893 cd m−2 for TDPM, respectively). Overall, our work provides a molecular design strategy of HLCT materials for efficient deep-blue OLED with high color purity using purely organic emitter.

Hybridized Local and Charge-Transfer Excited-State Fluorophores through the Regulation of the Donor–Acceptor Torsional Angle for Highly Efficient Organic Light-Emitting Diodes

Hybridized local and charge-transfer (HLCT) excited-state fluorophores, which enable full exciton utilization through a reverse intersystem crossing from high-lying triplet states to singlet state,...

Highly efficient nondoped blue electroluminescence based on hybridized local and charge-transfer emitter bearing pyrene-imidazole and pyrene

• A high-efficiency blue emitter is obtained based on pyrene[4,5- d ]imidazole and pyrene. • The nondoped blue OLED shows the maximum EQE of 9.13% with maximum exciton utilization efficiency of 65%. • Extremely small efficiency roll-offs of 0.9% and 6.9% are realized at high brightness of 10,000 and 50000 cd m −2 . Organic light-emitting diodes (OLEDs) have been explored and utilized in many fields of flat-panel displays nowadays because of their plentiful advantages such as lightweight, high flexibility, high picture quality, etc., and are hopeful to be the next-generation displays. However, improvements to the efficiency of blue OLEDs are still vital to OLEDs as replacements for liquid crystal display technology. A blue light-emitting material is one of the key components in the preparation of OLED displays. Designing molecule based on donor–acceptor (D-A) structure with a hybridized local and charge transfer (HLCT) excited state is a appealing strategy for providing an efficient OLED with high external quantum efficiency through efficacious exciton utilization. Herein, a highly efficient blue emitter, PyI-Py, is constructed combining pyrene[4,5- d ]imidazole (weak donor) and pyrene (weak acceptor). The non-doped blue OLED exhibits excellent performance with a maximum current efficiency of 15.74 cd A −1 , a maximum external quantum efficiency (η ext ) of 9.13% and a maximum brightness of as high as 91097 cd m −2 which is rarely obtained for a non-doped blue OLED. Moreover, the η ext can reach 9.05% at very high brightness of 10000 cd m −2 , displaying extremely low efficiency roll-off of 0.9% which displays great superiorities in contrast with most thermally activated delayed fluorescent materials. The device characteristics lie among the highest values in non-doped blue OLEDs based on HLCT emitter and correspond to the best performance achieved for non-doped pyrene-based blue OLEDs to date. A maximum exciton utilization efficiency of 65% is harvested. The superior performance is attributed to the proper donor–acceptor design strategy which results in a HLCT excited state with the generation of a high proportion of singlet excitons.