Search

A low lasing threshold of up to 0.27 μJ cm−1 was achieved by using TADF materials. Advanced light amplification architectures composed of dual DABNA derivatives were also demonstrated.

This work reports a new acceptor for constructing donor-acceptor type (D-A type) blue thermally activated delayed fluorescence (TADF) emitters with narrowed charge-transfer (CT) emissions. A new acceptor core, carbazole-2-carbonitrile (CCN), is formed by the fusion of carbazole and benzonitrile. Three D-A type TADF emitters based on the CCN acceptor, namely 3CzCCN, 3MeCzCCN, and 3PhCzCCN, have been successfully synthesized and characterized. These emitters show deep-blue emissions from 439 to 457 nm with high photoluminescence quantum yields of up to 85% in degassed toluene solutions. Interestingly, all CCN-based deep-blue TADF emitters result in narrow CT emissions with full-width at half-maximums (FWHMs) of less than 50 nm in toluene solutions, which are pretty narrower compared with those of typical D-A type TADF emitters. Devices based on these emitters show high maximum external quantum efficiencies of up to 17.5%.

Hyperfluorescent organic light-emitting diodes (HF-OLEDs) enable a cascading Förster resonance energy transfer (FRET) from a suitable thermally activated delayed fluorescent (TADF) assistant host to a fluorescent end-emitter to give efficient OLEDs with relatively narrowed electroluminescence compared to TADF-OLEDs. Efficient HF-OLEDs require optimal FRET with minimum triplet diffusion via Dexter-type energy transfer (DET) from the TADF assistant host to the fluorescent end-emitter. To hinder DET, steric protection of the end-emitters has been proposed to disrupt triplet energy transfer. In this work, the first HF-OLEDs based on structurally well-defined macromolecules, dendrimers is reported. The dendrimers contain new highly twisted dendrons attached to a Cibalackrot core, resulting in high solubility in organic solvents. HF-OLEDs based on dendrimer blend films are fabricated to show external quantum efficiencies of10% at 100 cd m

The limitation of lasing duration less than nanosecond order has been a major problem for realizing organic solid-state continues-wave (CW) lasers and organic semiconductor laser diodes. Triplets accumulation under CW excitation has been well recognized as a critical inhibiting factor. To overcome this issue, the utilization of thermally activated delayed fluorescence (TADF) emitters is a promising mechanism because of efficient reverse intersystem crossing. Herein, we model the triplet accumulation processes under lasing and propose the active utilization of TADF for lasing based on our simulation analysis. We used the rate constants experimentally determined from the optical properties of a boron difluoride curcuminoid fluorophore showing both TADF and lasing. We demonstrate that the intersystem crossing efficiency is gradually increased after the convergence of relaxation oscillation, i.e., terminating laser oscillation. In addition, we found that when the reverse intersystem crossing rate is close to the intersystem crossing rate, CW lasing becomes dominant.

There has been increasing interest in blue organic light-emitting diodes based on thermally activated delayed fluorescence (TADF). The construction of a fully optimized device architecture is crucial in accordance with developing high-performance materials because highly efficient electroluminescence cannot be realized without balancing both carrier injection and transport with decreasing several exciton loss processes. Thus, the detailed mechanism of carrier injection, transport, and recombination in emitting layers has to be clarified. In this study, various device architectures for a recently emerged blue TADF molecular system based on multiple donors and acceptors were systematically investigated, especially by focusing on the interlayers. This work also aims to offer guidelines for improving device stabilities. Our findings clarify the role of each layer, providing in-depth insight into device design and the selection of proper materials for each constituted layer.

Recently, there has been increasing interest in a class of polycyclic aromatic hydrocarbons (PAHs) with peri-extension of acenes. These peri-fused systems, referred to as peri-acenes and acenoacenes, are considered to be nanographenes.[1–3] Thus, the compounds based on tetracene and larger acenes show singlet biradical nature at the zigzag edge, offering unique and interesting properties. However, the synthesis schemes for these compounds are generally complicated, which hinder the extensive development of these derivatives and application to organic optoelectronics such as organic field-effect transistors (OFETs) and organic light-emitting diodes (OLEDs). A pentacene derivative with two triisopropylsilylethynyl groups at the central ring (TIPS-PEN) was developed in 2001. It shows good solubility, stability, and semiconducting property, resulting in being one of the most studied organic semiconductors. In contrast, the peri-extended compound of TIPS-PEN has not been developed because of the difficulty in synthesis using the same method as TIPS-PEN.[4] Here, we found the synthetic conditions to avoid the competition between 1,2- and 1,4-addition of lithium acetylide on large aromatic dione and succeeded in synthesizing TIPS-ethynyl-substituted peri-pentacenopentacene (TIPS-PPP).[5] The stability of TIPS-PPP was 16 times superior to that of TIPS-PEN, which is attributed to higher aromaticity as shown in an electronic structure of two-fused anthracene. TIPS-PPP shows the crystal packing of the 2D-brickwall motif like TIPS-PEN. The high mobility of up to 1 cm2 V−1 s−1 was obtained in OFET fabricated by wet process owing to large transfer integrals and low reorganization energies. In addition, TIPS-PPP showed high quantum yield in near-infrared (NIR) region. Thus, it was used as an emitter for NIR-OLED devices, resulting in high external quantum efficiency at 800 nm. These results suggest that acene-like materials are very promising for developing NIR emitters. References [1] M. Mamada, R. Nakamura, C. Adachi, Chem. Sci. 2021, 12, 552. DOI: 10.1039/D0SC04699J [2] T. Jousselin-Oba, M. Mamada, J. Marrot, A. Maignan, C. Adachi, A. Yassar, M. Frigoli, J. Am. Chem. Soc. 2019, 141, 9373. DOI: 10.1021/jacs.9b03488 [3] Y. Gu, Y. G. Tullimilli, J. Feng, H. Phan, W. Zeng, J. Wu, Chem. Commun. 2019, 55, 5567. DOI: 10.1039/c9cc01986c [4] X. Zhang, J. Li, H. Qu, C. Chi, J. Wu, Org. Lett. 2010, 12, 3946. DOI: 10.1021/ol101720e [5] T. Jousselin-Oba, M. Mamada, K. Wright, J. Marrot, C. Adachi, A. Yassar, M. Frigoli, Angew. Chem. Int. Ed. 2021, DOI: 10.1002/anie.202112794.

External quantum efficiency (EQE) roll-off under high current injection has been one of the major limiting factors toward the development of organic semiconductor laser diodes (OSLDs). While significant progress in this regard has been made on organic semiconductors (OSCs) emitting in the blue-green region of the visible spectrum, OSCs with longer wavelength emission (600 nm) have fallen behind in both material development and the advancement in device architectures suitable for the realization of OSLDs. Therefore, to make simultaneous incremental advancements, a host-guest system comprising of a high performing poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) polymer and an efficient small molecule laser dye, dithiophenyl diketopyrrolopyrrole (DT-DPP), is used. This combination provides an extremely low amplified spontaneous emission threshold of 4.2 µJ cm