Boosting the Efficiency of Near‐Infrared Fluorescent OLEDs with an Electroluminescent Peak of Nearly 800 nm by Sensitizer‐Based Cascade Energy Transfer

Abstract

A sensitization-based cascade energy transfer channel is proposed to boost the electroluminescent performances of the solution-processed near-infrared organic light-emitting devices (OLEDs) featuring an electroluminescent peak of 786 nm from a new fluorescent emitter of N 4 ,N 4 ,N 9 ,N 9tetra-p-tolylnaphtho[2,3-c][1,2,5]thiadiazole-4,9-diamine (NZ2mDPA) with unique aggregation-induced emission (AIE) property. The optimized device is composed of 4,4′-N,N-dicarbazole-biphenyl (CBP) as the host, bis(2phenyl-1,3-benzothiozolato-N,C 2′ )iridium (Ir(bt) 2 (acac)) as the sensitizer, and NZ2mDPA as the emitter, where the cascade energy transfer can occur via two steps realizing unexpected triplet-singlet energy transfer by the Förster mechanism. The first step features efficient triplet harvesting from CBP to Ir(bt) 2 (acac), and then the second step involves in resonant energy transfer from the phosphorescent sensitizer to the near-infrared AIE emitter of NZ2mDPA, which finally endows two channels of harvesting singlet and triplet excitons. The unique scheme achieves not only more efficient Förster energy transfer but also the higher utilization efficiency of triplet excitons. As a result, the near-infrared OLEDs can realize a factor of 2.7 enhancement of external quantum efficiency by employing the phosphor-sensitized AIE lumogen compared with the commonly used binary host-guest system.

Exploration of High Efficiency AIE‐Active Deep/Near‐Infrared Red Emitters in OLEDs with High‐Radiance

“…Similar to most of NZ‐based compounds, the targeted molecules of TNZPPI, TNZ t PPI, and TNZ2 t PPI (uniformly named as TNZPs) were synthesized by multistep coupling reaction as shown in Figure S1 (Supporting Information). First, the core intermediate product of NZ unit was prepared via the cyclization reaction between 2,3‐diaminonaphthalene and N ‐thionylaniline with a better yield of 77%, and the subsequent bromination procedure (DBr‐NZ) was operated using liquid bromine as Br‐donating moiety with an optimized yield of 64%. After then, the commercial TPA‐based boronic acid was introduced to connect with DBr‐NZ, and the monosubstituted intermediate of TNZ‐Br was obtained via classical palladium‐catalyzed Suzuki reaction.…”

“…Recently, a new building block named naphtho[2,3‐c][1,2,5]thiadiazole (NZ) as electronic acceptor has attracted more and more attention in constructing DR/NIR emitters by coupling with different donors on its both sides. Integrating with its derivatives' photophysical behaviors, OLEDs performance, and theoretical calculation, the hybrid localized and charge transfer (HLCT) mechanism plays an important role in their electroluminescence process, and the efficient upper reverse intersystem crossing (uRISC) activation from triplet excitons to singlet ones has improved their internal quantum efficiency (IQE) and the radiative transition proportion . For example, Yang group had realized 3.9% of external quantum efficiency (EQE) in nondoped devices via optimizing symmetrical derivatives as emitters, and Ma group fabricated two unsymmetrical emitters to achieve better performance with desirable internal quantum efficiency (IQE ≈ 100%) .…”

A cost‐effective crosslinked β‐cyclodextrin polymer for the rapid and efficient removal of micropollutants from wastewater

“…wileyonlinelibrary.com/journal/pi log q e = log K F + 1 n log C e (6) where C e (mmol L −1 ) is the equilibrium concentration of organic micropollutant, q max,e (mg g −1 ) and K L (L mmol −1 ) are Langmuir constants related to maximum adsorption capacity and binding energy, respectively, and K F and n are empirical constants that indicate the Freundlich constant and heterogeneity factor, respectively.…”

“…Polymers play important roles in everyday life, ranging from living apparatus to construction materials as well as solar cells, liquid crystals, supramolecular assemblies, etc. [1][2][3][4][5][6] On the other hand, organic micropollutants, such as plastic components, dye intermediates and pesticide intermediates, have caused serious pollution problems in the water environment resulting in negative effects to eco-systems and human life. [7][8][9][10][11] Despite a large research effort, [12][13][14][15][16] the removal of organic micropollutants from water is largely limited by low adsorption capacity, slow adsorption rate, poor removal rate and difficult regeneration processes.…”

Modulation of Thermally Activated Delayed Fluorescence in Waterborne Polyurethanes via Charge‐Transfer Effect

“…In the past decades, purely organicl uminescentm aterials have experienced ab ooming development due to their enormous applicationsi nc hemical sensors, [1][2][3][4] optoelectronics, [5][6][7][8][9] bioimaging [10][11][12][13][14][15] and data storage. [16][17][18][19][20][21] Especially,t hermally activated delayed fluorescence( TADF), [22][23][24][25][26] discovered as the second band of long-lived emission, shows identical contour with the prompt fluorescence( PF) and has been widely used in organic light-emitting diodes (OLEDs).…”