via endothermally assisted reverse intersystem crossing (RISC), thereby achieving a theoretical 100% exciton utilization. [1b,3,4] The strategy for a sufficiently small ΔE ST is to reduce the electron exchange of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) by separating them into different segments. [5][6][7][8] As a classic example, a donor-π-acceptor (D-π-A) molecular architecture can form a twisted conformation at excitation and induce effective charge transfer (CT) along with the HOMO (@ donor) and LUMO (@ acceptor) separation. [6,9] The structure relaxation between the ground and twist induced excited states, however, inevitably results in large Stokes shift and broad CT emission, which is extremely detrimental to the color purity of the emitters for high-resolution display applications.In an exceptional solution for this problem proposed by Hatakeyama et al., a series of N/B rigid heterocycles were used as multiple resonances induced TADF (MR-TADF) emitters based on a DABNA-1 core to show good color purity. [10] Different from the D-π-A type TADF emitters, these MR-TADF emitters possess a rigid configuration and realize the HOMO and LUMO separation by opposite resonance effect of the nitrogen and boron atoms. Very recently, by modifying the original DABNA-1 with a peripheral carbazole group, Zheng and co-workers obtained a more efficient MR-TADF emitter TBN-TPA, and the corresponding device realized a maximum external quantum efficiency (EQE max ) of 32.1% and a sharp blue emission peak with full-width at half-maximum (FWHM) of 27 nm, showing the potential of MR-TADF. [11] However, the attempts with oxygen atoms replacing nitrogen atoms as the electron-donating group in a polycyclic framework did not activate the TADF phenomenon, [12] indicating new MR-TADF systems need more investigation and the versatility of the molecular design should be further explored.In this work, we design a novel system bearing MR-TADF activity aside from the reported N/B system, which consists of rigidified aryl ketones and amine. In the previous study, carbonyl group was widely used as a functional motif for room temperature phosphorescent materials and TADF emitters, owing to the electron-withdrawing nature and the small ΔE ST caused by its electronic transition from the n orbital to Multiple resonances induced thermally activated delayed fluorescence (MR-TADF) has great advantages in high color purity display. Up to now, current MR-TADF emitters are only based on the boron-nitrogen-containing fragment. Reported herein is a novel class of MR-TADF emitter, quinolino[3,2,1-de]acridine-5,9-dione (QAO), realized by the opposite resonance effect of the carbonyl and the nitrogen atoms, which is also the smallest TADF emitter reported so far. The QAO-based pure blue organic light-emitting diode achieves a maximum external quantum efficiency (EQE max ) of 19.4% with a small full width at half maximum of 39 nm. Moreover, tert-butyl modified QAO can be employed as an efficient electr...

The design of flame-retardant biocomposites based on biobased flame retardants (FRs) represents a promising direction for creating a sustainable world. To date, it remains a major challenge to explore a green and scalable strategy for the design of highly effective, biobased FRs for bioplastics, such as polylactic acid (PLA). Herein, we have demonstrated a green, facile fabrication approach for a core–shell-structured biobased flame retardant (APP@CS@PA-Na) via layer-by-layer assembly using water as the assembly media. With electrostatic interactions, APP@CS@PA-Na was prepared by sequential assembly of ammonium polyphosphate (APP) with positively charged chitosan (CS) and then negatively charged phytic acid salt (PA-Na). The addition of APP@CS@PA-Na can enhance both the flame retardancy and the toughness of PLA. With the addition of 10 wt % APP@CS@PA-Na, the resultant PLA composite can pass an UL-94 V-0 rating and meanwhile shows an increased elongation at break by 28.4%, compared with that of neat PLA (8.1%). Through the analysis of the volatile gases and the residues, the flame retardant mechanism of APP@CS@PA-Na in PLA plays the key role in the condensed-phase. This work will broaden the practical application field of PLA, such as in electric and electronic and fibers fields.

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Charge transfer state (CT) plays an important role in exciton diffusion, dissociation, and charge recombination mechanisms. Enhancing the utilization and suppressing the recombination process of CT excitons is a promising way to improve the performance of organic solar cells (OSCs). Here, an effective method is presented via introducing a delayed fluorescence (DF) emitter 3,4-bis(4-(diphenylamino)phenyl) acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile (APDC-TPDA) in OSCs.The long-lifetime singlet excitons on APDC-TPDA can transfer to polymer donors to prolong exciton lifetime, which ensures sufficient time for diffusion and dissociation. Concurrently, the high triplet energy level (T 1 ) of the DF material can also prevent the reverse energy transfer from CT to T 1 . APDC-TPDA-containing ternary OSCs shows a high PCE of 16.96% with a reduced recombination energy loss of 0.46 eV. It is noteworthy that the ternary OSC also exhibits superior storage stability. After 55 days of storage, the PCE of the ternary OSC still retains about 96% of its primitive state. Furthermore, this ternary strategy is efficient and universally applicable to OSCs, and positive results can be obtained in different systems with different DF emitters. These results indicate that the ternary strategy provides a new design idea to realize high performance OSCs.

Emerging graphene/organic phototransistors are eye-catching technologies owing to their unique merits including easy/low-cost fabrication, temperature independent, and achieving various functions. However, their development in the near-infrared (NIR) region is experiencing a bottleneck of inferior sensitivity due to low exciton dissociation efficiency and inefficient charge extraction rate. Here, a novel-design solution-processed graphene/organic NIR phototransistor is reported, that is, creatively introducing electron extraction layer of ZnO on graphene channel and employing organic ternary bulk heterojunction as photosensitive layer, successfully breaking that bottleneck. The phototransistor exhibits a high responsivity of 6.1 × 10 6 A W −1 , a superior detectivity of 2.4 × 10 13 Jones, and a remarkable minimum detection power of 1.75 nW cm −2 under 850 nm radiation. Considering its excellent NIR detection performance, a noncontact transmission-type pulse monitoring is carried out with no external circuit support, from which human pulse signal and heart rate can be displayed in real time. The phototransistor, interestingly, can be switched into a photomemory function with a retention time of 1000 s in the atmosphere through a gate voltage of −20 V. The design takes the characteristics of graphene/organic phototransistors to a higher level, beyond the limit of sensitivity, and opens up a novel approach for developing multifunction devices.