Enhanced Pi Conjugation and Donor/Acceptor Interactions in D-A-D Type Emitter for Highly Efficient Near-Infrared Organic Light-Emitting Diodes with an Emission Peak at 840 nm

Abstract

Restricted by the energy gap rule, near-infrared (NIR) luminescent materials face great challenges. Here, we report a newly designed and synthesized organic molecule, 5,5′-([1,2,5]­thiadiazolo­[3,4-c]­pyridine-4,7-diyl)­bis­(N,N-diphenylthiophen-2-amine) (DTPS-PT), which has strong donor and acceptor interactions for NIR emission applications. The results demonstrate that the higher planarity of the DTPS-PT molecular structure enhances the pi-conjugation and hybridization between the charge transfer state (CT) and localized pi states (LE). As a result, DTPS-PT exhibits NIR emissions from an LE involved in hybridized local and charge transfer (HLCT) states, showing a 79% high fluorescence quantum yield in the low polar solvent tetrachloromethane. For both doped and nondoped devices, the NIR OLEDs based on DTPS-PT achieved “real” NIR emission with the λonset above 700 nm. The best performing OLED device within the doped devices gave a maximum emission peak around 840 nm with a maximum radiance of 2202 mW Sr–1 m–2.

Near‐Infrared Electroluminescence beyond 800 nm with High Efficiency and Radiance from Anthracene Cored Emitters

“…proposed an acute concept, real NIR emission, which denotes that the entire emission region should above 700 nm. [10] Thec orresponded NIR emitter DTPS-PT achieved amaximum radiance of 2202 mW Sr À1 m À2 at 840 nm with the l onset around 700 nm which set anew record for the NIR-OLEDs emitting over 800 nm. Despite the encouraging radiance data, the device efficiencyi sn ot reported indicating the challenges posed by the development of highly efficient organic NIR materials are still formidable.…”

“…Moreover,t he non-doped devices based on DCPA-TPAa nd DCPA-BBPAs howed NIR emission with emission peak at 838 and 916 nm and maximum EQEs of 0.58 %a nd 0.07 %, respectively.F urthermore,amaximum radiance of 20 707 mW Sr À1 m À2 was achieved for the further optimized non-doped device based on DCPA-TPA, which is about tenfold higher than the best-reported result with similar electroluminescence (EL) spectra. [10] Results and Discussion…”

A Simple Molecular Design Strategy for Delayed Fluorescence toward 1000 nm

“…This is common for highly polar TADF materials and is attributed to the effects of solvatochromism and aggregation. 7,28,36 This is also accompanied by a sequential decrease in PLQY, 16,28 indicating a trade-off between PL wavelength and quantum efficiency when exploiting aggregation to red-shift emission. When CAT-1 is doped into CBP at 40 wt %, emission is recorded at λ max = 820 nm with a TADF component still present (τ = 8 μs, 5.1% contribution) (Figures S13 and S18).…”

“…700–1000 nm). 4−7 The longest wavelength TADF emitter reported to date exhibits a maximum peak emission wavelength (λ max ) of ca. 800 nm, 8 marginally outside the visible spectrum, and considerably below the values of ≥1000 nm that are well established for first generation fluorescent emitters.…”

Near‐Infrared Electroluminescence beyond 800 nm with High Efficiency and Radiance from Anthracene Cored Emitters

“…Moreover, the non‐doped devices based on DCPA‐TPA and DCPA‐BBPA showed NIR emission with emission peak at 838 and 916 nm and maximum EQEs of 0.58 % and 0.07 %, respectively. Furthermore, a maximum radiance of 20 707 mW Sr −1 m −2 was achieved for the further optimized non‐doped device based on DCPA‐TPA, which is about tenfold higher than the best‐reported result with similar electroluminescence (EL) spectra [10] …”