Rong-Huei Yi

Two novel nona-coordinated red-emitting [Eu(btfa)₃(Ph-TerPyr)] (Eu-1) and [Eu(NTA)₃(Ph-TerPyr)] (Eu-2) were successfully synthesized and employed as EML to fabricate red-OLEDs. The overall EL performance of Eu-2 based device is two fold higher than Eu-1 based device.

Abstract

Two novel nona-coordinated Eu(III) complexes [Eu(btfa)₃(Ph-TerPyr)] (Eu-1) and [Eu(NTA)₃(Ph-TerPyr)] (Eu-2) have been synthesized and characterized. The structure of the complexes was elucidated by density functional theory (DFT) methods. The experimental photophysical properties of the complexes were investigated and complemented with theoretical calculations. Effective energy transfer (ET) pathways for the sensitized red luminescence is discussed. The complexes were tested as emitting layers (EML) in organic light emitting diodes (OLEDs). At the optimum doping concentration of 4 wt.%, the double-EML OLEDs of Eu-1 exhibited red electroluminescence (EL) with an EQE of 4.0 % and maximum brightness (B)=1179 cd/m², maximum current efficiency (η_c)=5.64 cd/A, and maximum power efficiency (η_p)=4.78 lm/W at the current density (J) of 10 mA/cm². Interestingly, the double-EML OLEDs of Eu-2 at the optimum concentration of 3 wt.%, displayed an outstanding EL performance with EQE of 7.32 % and B=838 cd/m², η_c=10.19 cd/A and η_p=10.33 lm/W at J=10 mA/cm². The EL performance of this device is among the best reported for devices incorporating a europium complex as a red emitter.

One-pot of Pd(II) catalyzed multiple C-H activation, via α,β-unsubstituted-BODIPYs react with 1,8-dibromonaphthalenes to obtain acenaphtho[b]-fused BODIPYs. These newly synthesized acenaphtho[b]-fused BODIPYs showed strong deep red absorptions/emissions and high fluorescence quantum yields.

Abstract

Aromatic ring fusion on BODIPY core can effectively tune its electronic property, and red-shift its absorption and emission wavelength. In this work, we report that a one-pot Pd(II) catalyzed multiple C−H activation to access acenaphtho[b]-fused BODIPYs though the reaction of α,β-unsubstituted-BODIPYs and 1,8-dibromonaphthalenes. These newly synthesized acenaphtho[b]-fused BODIPYs revealed intensified deep red absorptions (639–669 nm) and emissions (643–683 nm), with high fluorescence quantum yields (0.53–0.84) in dichloromethane. Notably, these acenaphtho[b]-fused BODIPYs exhibited well-defined self-aggregation behavior in water/THF mixture, and for instance, the absorption of 3 a was red-shifted by 53 nm to 693 nm after forming aggregates.

Cyan thermally activated delayed fluorescence molecules with aggregation-enhanced emission and horizontal dipole orientation can function as efficient emitter and sensitizing host to improve electroluminescence efficiencies and reduce efficiency roll-offs for OLEDs.

Abstract

Organic light-emitting diodes (OLEDs) using thermally activated delayed fluorescence (TADF) materials to sensitizing conventional fluorescence dopants (CFDs) have attracted intensive research interest due to the extraordinary device performances. Herein, a cyan luminogen (TCz-BP-SFAC) with TADF and aggregation-enhanced emission (AEE) character is developed as a sensitizing host for CFDs. TCz-BP-SFAC owns excellent thermal and electrochemical stabilities, prefers horizontal dipole orientation and demonstrates violent delayed fluorescence with high photoluminescence quantum yields in neat and doped films. It exhibits preeminent electroluminescence (EL) performances with maximum external quantum efficiencies (η _exts) of 25.1% and 30.0% and very low efficiency roll-offs. TCz-BP-SFAC also performs well as a sensitizing host for CFDs of different colors. When TCz-BP-SFAC sensitizing green emitter TTPA and orange emitter TBRB, the devices achieve high η _exts of 16.9% and 17.1% as well as very low efficiency roll-offs of 2.4% and 1.2%, respectively. Moreover, TCz-BP-SFAC can serve as a sensitizing host for two-color all-fluorescence white OLEDs, resulting in high η _exts of ∼18% and very low efficiency roll-offs of ∼5%. The outstanding EL performances predict the great potential of TCz-BP-SFAC as emitter and host in practical display and lighting devices.

Publication date: 15 April 2023

Source: Chemical Engineering Journal, Volume 462

Author(s): Ke-Ke Tan, Da-Wei Zhang, Wen-Long Zhao, Meng Li, Chuan-Feng Chen

Publication date: 1 May 2023

Source: Chemical Engineering Journal, Volume 463

Author(s): Jianan Xue, Shuonan Chen, Jie Liang, Hai Bi, Yu Liu, Yue Wang

Publication date: 1 April 2023

Source: Chemical Engineering Journal, Volume 461

Author(s): Yanqin Miao, Guoliang Wang, Mengna Yin, Yuanyuan Guo, Bo Zhao, Hua Wang

A review of recent advances in the field of long-wavelength light-emitting electrochemical cells from the viewpoints of materials and device engineering.

Two “V-shaped” red-to-NIR organic luminogens, FITPA and FIMPA, were developed. The “V-shaped” configurations have been demonstrated to enhance the transition dipole moments. Moreover, the ACQ-to-AIE transformation from FITPA to FIMPA is induced by a methoxy-substitution strategy. The enhanced transition dipole moment and AIE behavior endow FIMPA intense luminescence in the solid state. Furthermore, the promising cell-imaging performance verified the great potential of FIMPA in biological applications.

Abstract

Deep red/near-infrared (NIR, >650 nm) emissive organic luminophores with aggregation-induced emission (AIE) behaviours have emerged as promising candidates for applications in optoelectronic devices and biological fields. However, the molecular design philosophy for AIE luminogens (AIEgens) with narrow band gaps are rarely explored. Herein, we rationally designed two red organic luminophores, FITPA and FIMPA, by considering the enlargement of transition dipole moment in the charge-transfer state and the transformation from aggregation-caused quenching (ACQ) to AIE. The transition dipole moments were effectively enhanced with a “V-shaped” molecular configuration. Meanwhile, the ACQ-to-AIE transformation from FITPA to FIMPA was induced by a methoxy-substitution strategy. The experimental and theoretical results demonstrated that the ACQ-to-AIE transformation originated from a crystallization-induced emission (CIE) effect because of additional weak interactions in the aggregate state introduced by methoxy groups. Owing to the enhanced transition dipole moment and AIE behaviour, FIMPA presented intense luminescence covering the red-to-NIR region, with a photoluminescence quantum yield (PLQY) of up to 38 % in solid state. The promising cell-imaging performance further verified the great potential of FIMPA in biological applications. These results provide a guideline for the development of red and NIR AIEgens through comprehensive consideration of both the effect of molecular structure and molecular interactions in aggregate states.

Seeing red! Strong donor-acceptor diads based on novel imidazo-pyrazine-5,6-dicarbonitrile (IPDC) electron acceptors exhibit blue to near infrared emission, as well as delayed emission such as thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP). IPDC-PTZ carrying the electron donor phenothiazine (PTZ) was found to display dual emission, which was studied in detail by photophysical experiments and computational studies.

Abstract

Three donor-acceptor compounds based on the imidazo-pyrazine-5,6-dicarbonitrile (IPDC) acceptor were synthesized. The IPDC emitters exhibit blue to near-infrared (NIR) emission with up to 54 % photoluminescent quantum yield. 9,9-Dimethyl-9,10-dihydroacridine (ACR), phenoxazine (POX), and phenothiazine (PTZ) served as electron donors. IPDC-POX displayed NIR emission in toluene solution, while showing room-temperature phosphorescence in the solid state. IPDC-ACR exhibited yellow thermally activated delayed fluorescence. Interestingly, dual-emissive behavior as well as excitation-dependent thermally activated delayed fluorescence (TADF) was found for IPDC-PTZ, arising from the two conformers of phenothiazine derivatives. Overall, this work describes a novel strong electron acceptor from the fusion of imidazole, pyrazine, and nitrile functional groups into one conjugated heterocycle for materials exhibiting NIR emission, TADF, and/or room-temperature phosphorescence (RTP).