Imidazo[1,2‐<i>a</i>]pyridine as an Electron Acceptor to Construct High‐Performance Deep‐Blue Organic Light‐Emitting Diodes with Negligible Efficiency Roll‐Off

Cao

et al. 2022

J. Phys. Chem. C

Charge transfer plays an important role in photophysical and photochemical reactions. However, the factors affecting the excited chargetransfer state are unclear. Here, two donor−π−acceptor dyads with an excellent blue fluorescence quantum yield are designed by integrating 1,2-diphenylphenanthroimidazole (PPI) as an electron donor and 1,2,4-triazolopyridine (TP) as an electron acceptor through phenyl (P) bridges. In the solvents dichloromethane (DCM) and dimethyl formamide (DMF), the dynamics of intramolecular charge transfer (ICT) of the two dyads (TP-P-PPI and TP-P-P-PPI) is located at the Marcus normal region, while the dynamics of charge recombination (CR) is situated at the Marcus inverted region. Therefore, TP-P-P-PPI with a long π-chain exhibits a longer lifetime of ICT but a shorter lifetime of CR than TP-P-PPI does with a short π-chain. In contrast, when the two dyads are spin-coated into a film, the dynamics of ICT and CR processes of the two dyads are restored to be positively correlated with the π-chain length because of the inhibition of intramolecular torsion between PPI and TP in the excited state of the film. This work demonstrates a specific approach via the molecular torsion to tune the dynamics of the ICT and CR among donor−π−acceptor systems.

Section: Introductionmentioning

confidence: 99%

Unveiling the π-Chain Effect on Charge Transfer and Charge Recombination Among Donor−π–Acceptor Material Systems

Cao

et al. 2022

J. Phys. Chem. C

“…Such prominent thermal stability should be ascribed to the bulky grid PI skeleton, which is conducive to the formation of uniform amorphous film and of vital importance for applications in organic electronic devices. [ 32 ] Moreover, the AFM was also performed to investigate the film‐forming ability. As shown in Figure S9, Supporting Information, the 2D and 3D AFM micrographs reveal that the film of PHT‐PPI prepared through spin coating in DCM is smooth and homogeneous, with RMS roughness of 0.324 nm, showing that PHT‐PPI has excellent film‐forming ability during device fabrication.…”

Section: Resultsmentioning

confidence: 99%

Effective Energy Transfer for Green, Orange, and Red Phosphorescent Organic Light‐Emitting Diodes Based on a Bipolar Deep‐Blue Emitter with Low Efficiency Roll‐Off at High Brightness

Advanced Photonics Research

Zhu

Tang

et al. 2021

Self Cite

Of paramount significance in phosphorescent organic light‐emitting diodes (PHOLEDs) are the facts that Förster resonance energy transfer (FRET) must be sufficient and back energy transfer should be prohibited. Herein, the FRET efficiencies for high‐performance PHOLEDs based on a simple bipolar luminogen 1‐phenyl‐2‐(5′‐phenyl‐[1,1′:3′,1″‐terphenyl]‐4‐yl)‐1H‐phenanthro[9,10‐d]imidazole (PHT‐PPI) with high triplet energy of 2.44 eV are systematically investigated. As a result, with PO‐01 as dopant, the high‐performance orange PHOLED is achieved with maximum external quantum efficiency (EQEmax) of 26.14% and ultrahigh brightness of 152 000 cd m−2, which are the highest reported efficiencies for orange OLEDs with such high brightness. In addition, the green and red PHOLEDs are also fabricated with EQEmax of 15.38% and 16.12%, respectively. Furthermore, the nondoped device based on PHT‐PPI as a deep‐blue emitter is also obtained with an EQEmax of 5.12% and the Commission Internationale de L’Eclairage (CIE) index of (0.15, 0.08). More importantly, the blue, green, orange, and red devices exhibit low efficiency roll‐off, particularly, of which the orange PHOLED is extremely small (<9%) even at the brightness of 10 000 cd m−2.

“…[36] It has been proved that indolo[3,2,1-jk]carbazole (ICz) and Imidazo[1,2-a]pyridine (IP), which has the moderate LUMO values of À 1.25 eV and À 0.83 eV, respectively. They can be employed as suitable electron acceptors to build blue DÀ A architecture molecule, [37,38] connecting with the donor, phenanthroimidazole (PI), which is recognized as a deep-blue luminous unit that had bipolar character. [39,40] In our previous work, we ever reported two high-efficiency blue DÀ A structure emitters ICz-PPI and IP-PPI.…”

Section: Introductionmentioning

confidence: 99%

“…However, the nondoped devices based on ICz-PPI and IP-PPI were obtained with unsatisfactory EQE max of 2.47 % and 4.86 %, respectively. [41,38] To further improve their performance, in this study, by inserting anthracene into these two emitters, ICz-An-PPI and IP-An-PPI featuring different acceptor groups were designed and synthesized (see Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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

Zheng

Huang

et al. 2021

Chemistry A European J

Self Cite

Acquiring desirable device performance with deepblue 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 nondoped OLEDs using ICz-An-PPI and IP-An-PPI as the emitting layers showed efficient blue emission with an external quantum efficiency (EQE max ) 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 CE max of 5.83 cd A À 1 , EQE max 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 EQE max 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 CIE y < 0.12. Such high performance may be attributed to the hot exciton HLCT mechanism via T 7 to S 2 . Our work may provide a new approach for designing high-efficiency deepblue materials.