A pure organic molecule 2,6-di­(phenothiazinyl)­naphthalene (DPTZN) with room-temperature phosphorescence (RTP) features was developed. Remarkably, a triazine-benzimidazole-based molecule TRZ-BIM can significantly improve the RTP efficiency of DPTZN in DPTZN:TRZ-BIM blend films. The photoluminescence quantum yield (PLQY) of 10 wt % DPTZN:TRZ-BIM blend film is 38%. The RTP property of DPTZN:TRZ-BIM blend films was characterized by steady, time-resolved, and temperature-dependent emission spectra. An organic light-emitting diode (OLED) with 10 wt % DPTZN:TRZ-BIM blend film as the emitting layer showed a high maximum external quantum efficiency of 11.5%, current efficiency of 33.8 cd A–1, and power efficiency of 32.6 lm W–1. Herein, we have developed an efficient approach to achieve precious-metal-free organic films that can be employed to fabricate high-performance phosphorescence OLEDs.

The development of efficient red thermally activated delayed fluorescence (TADF) emitters with an emission wavelength beyond 600 nm remains a great challenge for organic light-emitting diodes (OLEDs). Herein, two pairs of isomers are designed and synthesized by attaching electron-donor 9,9-diphenyl-9,10-dihydroacridine (DPAC) moiety to the different positions of two kinds of highly rigid planar acceptor cores (PDCN and PPDCN). Their TADF efficiencies and emission maxima (599-726 nm) are regulated by molecular isomer manipulation. Interestingly, the photoluminescence quantum yields (Φ PL s) of trans-isomers T-DA-1 and T-DA-2 (78% and 89%) are remarkably higher than those of their corresponding cis-isomers C-DA-1 and C-DA-2 (12% and 14%). Significantly increased Φ PL values can be explained by single crystal structures and theoretical simulation. As a result, a deep red TADF-OLED based on T-DA-2 displays a maximum external quantum efficiency (EQE) of 26.26% at 640 nm. Notably, at a brightness of 100 cd m −2 , the EQE value of T-DA-2-based device still remains at an extremely high level of 23.95%, representing the highest value for reported red TADF-OLEDs at the same brightness. These results provide a reasonable pathway to optimize optoelectronic properties and thereby construct efficient red TADF emitters through rational isomer engineering.

Systematic and detailed research on mechanochromic luminescence reveals the conformational isomerization mechanism behind single-molecule white-light emission.

number of one-compound-based efficient white light photoluminescence (PL) have been reported. [3] The performance of the single-emitter-based WOLEDs should be improved. [4] As a consequence, highly efficient organic white electroluminescence (EL) based on one emissive compound is still a great challenge. A fundamental issue is to construct organic molecules that can form two kinds of electron-injection-induced excited states with blue and yellow emission characteristics. Furthermore, elucidating and understanding the mechanism of organic molecules with dual emission behaviors is also very important, which can promote to establish a molecular design strategy for this class of molecules. For ideal WOLEDs, the yellow emissive excited states should have thermally activated delayed fluorescence (TADF) [5] or phosphorescence [6] properties to harvest the electro-generated excited states and reach the highest internal quantum efficiency of 100%.In this contribution, we report an organic molecule PTZ-BP composed of phenothiazine (PTZ) as an electron donor and benzophenone (BP) as an electron acceptor (Scheme S1, Supporting Information). The model compound phenyl-phenothiazine (PhPTZ) was employed as reference in this study. PTZ-BP-based solid or solution displays dual emissive property and the luminescent spectra are constituted by a prompt fluorescence at around 440 nm and a delayed fluorescence at around 550 nm resulting in the generation of white light. The very simple molecular structure of PTZ-BP provides an ideal model for understanding the mechanism of organic molecules with dual emission feature. More importantly, PTZ-BP has been employed to fabricate efficient WOLEDs based on a single emitter. So far, a few white organic compounds with prompt and delayed fluorescence have been reported. [3a] However, only PL was achieved and efficient EL remains a great challenge for this kind of system. The EL property, presented in this study, provides a promising strategy for developing high-performance WOLEDs based on pure organic luminescent materials.The molecular structures of PTZ-BP and PhPTZ are presented in Figure 1a. by nucleophile substitution reaction in high yield and fully characterized by 1 H and 13 C NMR, mass spectrometry, and elemental analysis (see the Supporting Information). Finally, the product was purified two times by vacuum sublimation approach. The obtained PTZ-BP sample displayed very high purity of 99.92%The design and synthesis of one-compound-based white light organic solids that can be employed to fabricate efficient organic white light-emitting devices (OLEDs) still remains a challenge. In this contribution, a classic organic donor-acceptor (D-A) type molecule (PTZ-BP) is presented, which is composed of phenothiazine (PTZ) as an electron donor and benzophenone (BP) as an electron acceptor. Intriguingly, PTZ-BP displays dual emission and thermally activated delayed fluorescence properties. Its dual emission originates from locally excited state and intramolecular charge transfer excited stat...