Carbazole/α-carboline hybrid bipolar compounds as electron acceptors in exciplex or non-exciplex mixed cohosts and exciplex-TADF emitters for high-efficiency OLEDs

Abstract

Electron acceptors based on the electron-deficient carboline of CbPyCN exhibited better electroluminescence performance than CzPyCN in exciplex or non-exciplex mixed cohosts and exciplex-emitters.

Aggregation-Induced Fluorescence of Carbazole and o-Carborane Based Organic Fluorophore

“…This blue shift effect could be attributed to the wider HOMO/LUMO energy gap on Cz fragment caused by the highly electron-deficient o -carborane (Cb) moiety of 2 (Yokoyama et al, 2018). Moreover, the formation of Cb cluster in 2 leads to the disruption of donor-linker-acceptor conjugated system (Cz-phenylacetylene), hence the absorption band of intramolecular charge transfer transition at 330 nm is highly reduced (Wang et al, 2018; Wu Q. J. et al, 2018), as evidenced in Figure 2.…”

“…As we formerly discussed, in THF solution the fluorescent emission of 1 comes from the local excited-state emission of a Cz-phenylacetylene conjugated fragment, which no longer exists in 2 because of the introduction of Cb moiety (Nghia et al, 2018a). Also, the ICT quenching effect caused by the highly electron-deficient Cb inhibits the fluorescent emission of 2 (Wu Q. J. et al, 2018). Hence in THF solution, compound 1 exerts a much stronger fluorescence intensity than 2 .…”

Design of Efficient Exciplex Emitters by Decreasing the Energy Gap Between the Local Excited Triplet (3LE) State of the Acceptor and the Charge Transfer (CT) States of the Exciplex

“…TX unit is promising as an acceptor unit to construct the efficient pure TADF (Wang et al, 2014; Li et al, 2016) While, TX derivatives have never been used as the acceptor molecule to construct the exciplex, we functionalized the TX unit by bridging it along with the terpyridy by Suzuki coupling reactions, an electron-withdrawing group, to obtain the molecules TX-TerPy. In exciplex, molecules containing nitrogen heterocycles are always preferred acceptors due to their deep HOMO levels (Shan et al, 2016; Deksnys et al, 2017; Nagai et al, 2017; Wu et al, 2018). TX-TerPy was successfully synthesized as shown in Scheme S1 and fully characterized by 1 H NMR spectroscopy (Figure S1), High-resolution EI-mass spectrometry (Figure S2), and satisfactory element analysis.…”

N-Benzoimidazole/Oxadiazole Hybrid Universal Electron Acceptors for Highly Efficient Exciplex-Type Thermally Activated Delayed Fluorescence OLEDs

“…Thus, the first generation of traditional fluorescent OLEDs which solely harvest singlet excitons only shows 25% of maximum internal quantum efficiency (IQE) (Wen et al, 2005). On the other hand, the second generation of phosphorescent OLEDs (PHOLEDs) based on heavy metal complexes and third generation of thermally activated delayed fluorescence (TADF) OLEDs could both reach 100% IQE in theory by utilizing all singlet and triplet excitons through intersystem crossing (ISC) and reverse inter-system crossing (RISC), respectively (Baldo et al, 1998; Adachi et al, 2001; Su et al, 2008; Lo et al, 2009; Goushi et al, 2012; Uoyama et al, 2012; Zhang and Forrest, 2012; Li et al, 2016; Cao et al, 2017; Huang et al, 2018; Wu Q. et al, 2018). However, to avoid consuming noble metals and achieving reliable true-blue light, TADF OLEDs based on low-cost pure organic emitters have attracted increasing interests as an alternative mechanism to PHOLEDs.…”

“…However, to avoid consuming noble metals and achieving reliable true-blue light, TADF OLEDs based on low-cost pure organic emitters have attracted increasing interests as an alternative mechanism to PHOLEDs. TADF emission is realized by an up-conversion process from lower energy triplet states to slightly higher energy singlet states by endothermic reverse inter-system crossing process (Li et al, 2016; Cao et al, 2017; Huang et al, 2018; Wu Q. et al, 2018). Therefore, a small singlet-triplet energy bandgap (Δ E ST ) is required for TADF emitters.…”