Significant efforts have been made to develop high-efficiency organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) emitters with blue, green, yellow, and orange-red colors. However, efficient TADF materials with colors ranging from red, to deep-red, to near-infrared (NIR) have been rarely reported owing to the difficulty in molecular design. Herein, we report the first NIR TADF molecule TPA-DCPP (TPA=triphenylamine; DCPP=2,3-dicyanopyrazino phenanthrene) which has a small singlet-triplet splitting (ΔEST ) of 0.13 eV. Its nondoped OLED device exhibits a maximum external quantum efficiency (EQE) of 2.1 % with a Commission International de L'Éclairage (CIE) coordinate of (0.70, 0.29). Moreover, an extremely high EQE of nearly 10 % with an emission band at λ=668 nm has been achieved in the doped device, which is comparable to the most-efficient deep-red/NIR phosphorescent OLEDs with similar electroluminescent spectra.

In this paper, a unique strategy is proposed to modulate fluorescence color of carbon dots (CDs) under both aqueous solution and solid state for bright multicolor light-emitting diodes (LEDs) applications. We report facile synthesis of dual-peak-emissive CDs with self-quenching-resistant character under solid state through hydrothermal method, and investigate the origins of dual-peak emission for the first time. In addition, based on the unique dual-peak-emissive phenomenon, acidmediated PL behaviors were realized by changing the pH value of hydrothermal precursors. We realized the color-tunable fluorescence under aqueous solution from blue (B-CDs) to yellow-green (YG-CDs) color and solid state from yellow to orangered color. The changed PL behaviors are attributed to the more conjugated structure inside CDs due to elevated carbonization degree. Furthermore, the red-shifted fluorescence from aqueous solution to solid state is ascribed to supramolecular cross-linking between adjacent particles. Thus, by manipulating the supramolecular cross-linking degree of YG-CDs in PVA, a series of luminescent blue-shifted CDs/PVA composite phosphors were obtained. Finally, we fabricate the almost full-color and white color LEDs with decent performances, which indicate their potential for solid-state lighting applications.

Highly efficient long-wavelength thermally activated delayed fluorescence (TADF) materials are developed using 2,3-dicyanopyrazino phenanthrene (DCPP) as the electron acceptor (A), and carbazole (Cz), diphenylamine (DPA), or 9,9-dimethyl-9,10-dihydroacridine (DMAC) as the electron donor (D). Because of the large, rigid π-conjugated structure and strong electron-withdrawing capability of DCPP, TADF molecules with emitting colors ranging from yellow to deep-red are realized with different electron-donating groups and π-conjugation length. The connecting modes between donor and acceptor, that is, with or without the phenyl ring as π-bridge, are also investigated to study the π-bridge effect on the thermal, photophysical, electrochemical, and electroluminescent properties. Yellow, orange, red, and deep-red organic light-emitting diodes (OLEDs) based on DCPP derivatives exhibit high efficiencies of 47.6 cd A (14.8%), 34.5 cd A (16.9%), 12.8 cd A (10.1%), and 13.2 cd A (15.1%), with Commission Internationale de L'Eclairage (CIE) coordinates of (0.44, 0.54), (0.53, 0.46), (0.60, 0.40), and (0.64, 0.36), respectively, which are among the best values for long-wavelength TADF OLEDs.

Significant efforts have been made to develop highefficiency organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) emitters with blue,g reen, yellow, and orange-red colors.H owever,e fficient TADF materials with colors ranging from red, to deep-red, to near-infrared (NIR) have been rarely reported owing to the difficulty in molecular design. Herein, we report the first NIR TADF molecule TPA-DCPP (TPA = triphenylamine; DCPP = 2,3-dicyanopyrazino phenanthrene) which has asmall singlet-triplet splitting (DE ST )of0.13 eV.Its nondoped OLED device exhibits am aximum external quantum efficiency (EQE) of 2.1 %w ith aC ommission International de L'Éclairage (CIE) coordinate of (0.70, 0.29). Moreover,a n extremely high EQE of nearly 10 %with an emission band at l = 668 nm has been achieved in the doped device,w hich is comparable to the most-efficient deep-red/NIR phosphorescent OLEDs with similar electroluminescent spectra.

A high external quantum efficiency of 7.68% was achieved in a near-infrared organic light-emitting diode with a novel TADF molecule.

Herein, a new bis(salicylaldiminato)Zn(ii) Schiff base complex, BTZn, derived from benzo[c][1,2,5]thiadiazole-5,6-diamine was designed and synthesized. It exhibited unique mechanical force-induced luminescence change characteristic. Upon mechanical grinding, the as-prepared BTZn solid crystalized from an ethanol/dichloromethane solution displays a high-contrast emission-colour variation from yellow (emission maximum λem = 545 nm) to red (λem = 645 nm), and this emission variation can be erased through solvent vapour treatment. The reversible emission colour alteration between yellow and red can be repeatedly performed. Thermal annealing of the as-prepared BTZn solid resulted in a more ordered orange phase with an emission maximum of 575 nm. The multi-stimuli-responsive luminescence mechanism has been investigated via SEM, powder X-ray diffraction (XRD), and thermal analyses. It is demonstrated that mechanical force can induce morphology transformation from the crystalline to the amorphous phase, which is accompanied by a change in the BTZn molecular packing modes. The BTZn-based solids have molecular packing-dependent emission characteristics. The XRD experimental results reveal that for the yellow emissive as-prepared BTZn solid, a columnar square molecular arrangement is adopted. On the other hand, the BTZn complex exhibits the ability to organize into organic luminescent gels constructed by one-dimensional BTZn molecular nanofibrils. The BTZn xerogel also displays mechanochromic properties. Accordingly, BTZn-based solids may be potential candidates for the development of new stimuli-responsive materials.

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Here, we showcase the impressive stimuli-responsive properties of a luminescent zinc(ii)–salophen complex CN-Zn, highlighting a reversible mechanochromic property.