Harvesting triplet excitons for near-infrared electroluminescence via thermally activated delayed fluorescence channel

Abstract

Near-infrared (NIR) emission is useful for numerous practical applications, such as communication, biomedical sensors, night vision, etc., which encourages researchers to develop materials and devices for the realization of efficient NIR organic light-emitting devices. Recently, the emerging organic thermally activated delayed fluorescence (TADF) emitters have attracted wide attention because of the full utilization of electron-generated excitons, which is crucial for achieving high device efficiency. Up to now, the TADF emitters have shown their potential in the deep red/NIR region. Considering the color purity and efficiency, however, the development of NIR TADF emitters still lags behind RGB TADF emitters, indicating that there is still much room to improve their performance. In this regard, this perspective mainly summarizes the past progress of molecular design on constructing TADF NIR emitters. We hope this perspective could provide a new vista in developing NIR materials and enlighten breakthroughs in both fundamental research and applications.

Non-toxic near-infrared light-emitting diodes

“…To overcome these drawbacks, metal-free TADF and traditional “purely fluorescent” materials emerged as potential candidates in tackling the ample range of challenges (e.g., non-toxicity, efficiency, bandwidth, and so on) ( Yu et al., 2021 ). Similar to phosphorescent organometallic emitters, TADF emitters can theoretically harvest all singlet and triplet excitons for light emission and hence theoretically achieve 100% internal quantum efficiencies ( Guo et al., 2017 ; Kaji et al., 2015 ).…”

A solution-processable near-infrared thermally activated delayed fluorescent dye with a fused aromatic acceptor and aggregation induced emission behavior

“…By far the most common and well established strategy for the design of TADF dyes has been the connection of polycyclic aromatic electron donors (D) and acceptors (A) via twisted linkages. [10][11][12] For example, toward efficient NIR TADF, 13,14 specialized rigid (low non-radiative loss) electron acceptors have been developed that present both a low local triplet energy (small DE ST ) and a high electron affinity (narrow band-gap). [15][16][17][18][19][20][21][22][23] Such properties are usually achieved through adopting an extended fused p system with numerous electron withdrawing moieties e.g.…”

Efficient narrowband electroluminescence based on a hetero-bichromophore thermally activated delayed fluorescence dyad

“…6,7 To achieve an effective RISC process, the general strategy is to reduce the exchange energy between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) by constructing a donor-acceptor (D-A) type emitter with a twisted structure. [8][9][10][11] However, the subsequent conformation relaxation caused by the twisted structures usually enhances the structure relaxation and leads to a wide emission with a full-width at half maximum (FWHM) of 470 nm, which is unsuitable for commercial displays. 12 To withstand the broadened FWHM of conventional D-A-type TADF emitters, Hatakeyama et al proposed the multi-resonance (MR) TADF emitter named DABNA-1, which exhibited a pure blue emission centered at 459 nm with an external quantum efficiency (EQE) of 13.5% and an impressively small FWHM of 28 nm.…”