De Novo Design of Excited-State Intramolecular Proton Transfer Emitters via a Thermally Activated Delayed Fluorescence Channel.

Developing excited-state intramolecular proton transfer (ESIPT) emitters with high photoluminescence quantum yields (ΦPLs) and long fluorescence lifetimes in solid state remains a formidable challenge. In this study, we integrated the molecular design tactics of thermally activated delayed fluorescence (TADF) into ESIPT molecules with the goals of improving their ΦPLs and increasing their fluorescence lifetimes. Two proof-of-concept molecules, PXZPDO and DMACPDO, were developed by adopting symmetric D-π-A-π-D molecular architectures (where D and A represent donors and acceptors, respectively) featuring electron-donating phenoxazine or a 9,9-dimethyl-9,10-dihydroacridine moiety, an ESIPT core ß-diketone, and phenylene π-bridges. Both molecules exhibited sole enol-type forms stabilized by intramolecular hydrogen bonds and exhibited a unique and dynamic ESIPT character that was verified by transient absorption analyses. Endowed with distinct TADF features, PXZPDO and DMACPDO showed high ΦPLs of 68% and 86% in the film state, coupled with notable delayed fluorescence lifetimes of 1.33 and 1.94 µs, respectively. Employing these ESIPT emitters successfully achieved maximum external quantum efficiencies (ηexts) of 18.8% and 23.9% for yellow and green organic light-emitting diodes (OLEDs), respectively, which represent the state-of-the-art device performances for ESIPT emitters. This study not only opens a new avenue for designing efficient ESIPT emitters with high ΦPLs and long fluorescence lifetimes in solid state but also unlocks the huge potential of ESIPT emitters in realizing high-efficiency OLEDs.

Optimizing Optoelectronic Properties of Pyrimidine-Based TADF Emitters by Changing the Substituent for Organic Light-Emitting Diodes with External Quantum Efficiency Close to 25 % and Slow Efficiency Roll-Off.

A series of green butterfly-shaped thermally activated delayed fluorescence (TADF) emitters, namely PXZPM, PXZMePM, and PXZPhPM, are developed by integrating an electron-donor (D) phenoxazine unit and electron-acceptor (A) 2-substituted pyrimidine moiety into one molecule via a phenyl-bridge π linkage to form a D-π-A-π-D configuration. Changing the substituent at pyrimidine unit in these emitters can finely tune their emissive characteristics, thermal properties, and energy gaps between the singlet and triplet states while maintaining frontier molecular orbital levels, and thereby optimizing their optoelectronic properties. Employing these TADF emitters results in a green fluorescent organic light-emitting diode (OLED) that exhibits a peak forward-viewing external quantum efficiency (EQE) close to 25 % and a slow efficiency roll-off characteristic at high luminance.

Adamantane-based wide-bandgap host material: blue electrophosphorescence with high efficiency and very high brightness.

An adamantane-based host material, namely, 4-{3-[4-(9H-carbazol-9-yl)phenyl]adamantan-1-yl}benzonitrile (CzCN-Ad), was prepared by linking an electron-donating carbazole unit and an electron-accepting benzonitrile moiety through an adamantane bridge. In this approach, two functional groups were attached to tetrahedral points of adamantane to construct an "sp(3)" topological configuration. This design strategy endows the host material with a high triplet energy of 3.03 eV due to the disruption of intramolecular charge transfer. Although CzCN-Ad has a low molecular weight, the rigid nonconjugated adamantane bridge results in a glass transition temperature of 89 °C. These features make CzCN-Ad suitable for fabricating blue phosphorescent organic light-emitting diodes (PhOLEDs). The devices based on sky-blue phosphor bis[(4,6-difluorophenyl)pyridinato-N,C(2')](picolinato)iridium(III) (FIrpic) achieved a high maximum external quantum efficiency (EQE) of 24.1%, which is among the best results for blue PhOLEDs ever reported. Furthermore, blue PhOLEDs with bis(2,4-difluorophenylpyridinato)-tetrakis(1-pyrazolyl)borate iridium(III) (FIr6) as dopant exhibited a maximum EQE of 14.2% and a maximum luminance of 34 262 cd m(-2). To the best of our knowledge, this is the highest luminance ever reported for FIr6-based PhOLEDs.

Aptamer Sensors for the Detection of Antibiotic Residues- A Mini-Review.

Food security is a global issue, since it is closely related to human health. Antibiotics play a significant role in animal husbandry owing to their desirable broad-spectrum antibacterial activity. However, irrational use of antibiotics has caused serious environmental pollution and food safety problems; thus, the on-site detection of antibiotics is in high demand in environmental analysis and food safety assessment. Aptamer-based sensors are simple to use, accurate, inexpensive, selective, and are suitable for detecting antibiotics for environmental and food safety analysis. This review summarizes the recent advances in aptamer-based electrochemical, fluorescent, and colorimetric sensors for antibiotics detection. The review focuses on the detection principles of different aptamer sensors and recent achievements in developing electrochemical, fluorescent, and colorimetric aptamer sensors. The advantages and disadvantages of different sensors, current challenges, and future trends of aptamer-based sensors are also discussed.

Realizing Highly Efficient Solution-Processed Homojunction-Like Sky-Blue OLEDs by Using Thermally Activated Delayed Fluorescent Emitters Featuring an Aggregation-Induced Emission Property.

Two new blue emitters, i.e., bis-[2-(9,9-dimethyl-9,10-dihydroacridine)-phenyl]-sulfone ( o-ACSO2) and bis-[3-(9,9-dimethyl-9,10-dihydroacridine)-phenyl]-sulfone ( m-ACSO2), with reserved fine thermally activated delayed fluorescent (TADF) nature and simply tuned thermal and optoelectronic properties, were synthesized by isomer engineering. The meta-linking compound, i.e., m-ACSO2, obtains the highest photoluminescence quantum yield with a small singlet-triplet energy gap, a moderate delayed fluorescent lifetime, excellent solubility, and neat film homogeneity. Due to its unique aggregation-induced emission (AIE) character, neat film-based heterojunction-like organic light-emitting diodes (OLEDs) are achievable. By inserting an excitonic inert exciton-blocking layer, the PN heterojunction-like emission accompanied by intefacial exciplex was shifted to a homojunction-like channel mainly from the AIE emitter itself, providing a new tactic to generate efficient blue color from neat films. The solution-processed nondoped sky-blue OLED employing m-ACSO2 as emitter with homojunction-like emission achieved a maximum external quantum efficiency of 17.2%. The design strategies presented herein provide practical methods to construct efficient blue TADF dyes and realize high-performance blue TADF devices.

Asymmetrical Ladder-Type Donor-Induced Polar Small Molecule Acceptor to Promote Fill Factors Approaching 77% for High-Performance Nonfullerene Polymer Solar Cells.

In this work, an effectual strategy of constructing polar small molecule acceptors (SMAs) to promote fill factor (FF) of nonfullerene polymer solar cells (PSCs) is first reported. Three asymmetrical SMAs of IDT6CN, IDT6CN-Th, and IDT6CN-M, which own large dipole moments, are designed and synthesized. The PSCs based on three polar SMAs exhibit apparently higher FFs compared with their symmetrical analogues. The asymmetrical design strategy accompanied with side chain and end group engineering makes IDT6CN-Th- and IDT6CN-M-based nonfullerene PSCs achieve high power conversion efficiency with FFs approaching 77%.

Fine-Tuning of Molecular Packing and Energy Level through Methyl Substitution Enabling Excellent Small Molecule Acceptors for Nonfullerene Polymer Solar Cells with Efficiency up to 12.54.

A novel small molecule acceptor MeIC with a methylated end-capping group is developed. Compared to unmethylated counterparts (ITCPTC), MeIC exhibits a higher lowest unoccupied molecular orbital (LUMO) level value, tighter molecular packing, better crystallites quality, and stronger absorption in the range of 520-740 nm. The MeIC-based polymer solar cells (PSCs) with J71 as donor, achieve high power conversion efficiency (PCE), up to 12.54% with a short-circuit current (JSC ) of 18.41 mA cm-2 , significantly higher than that of the device based on J71:ITCPTC (11.63% with a JSC of 17.52 mA cm-2 ). The higher JSC of the PSC based on J71:MeIC can be attributed to more balanced µh /µe , higher charge dissociation and charge collection efficiency, better molecular packing, and more proper phase separation features as indicated by grazing incident X-ray diffraction and resonant soft X-ray scattering results. It is worth mentioning that the as-cast PSCs based on MeIC also yield a high PCE of 11.26%, which is among the highest value for the as-cast nonfullerene PSCs so far. Such a small modification that leads to so significant an improvement of the photovoltaic performance is a quite exciting finding, shining a light on the molecular design of the nonfullerene acceptors.

Inheriting the Characteristics of TADF Small Molecule by Side-Chain Engineering Strategy to Enable Bluish-Green Polymers with High PLQYs up to 74% and External Quantum Efficiency over 16% in Light-Emitting Diodes.

Thermally activated delayed fluorescence (TADF) polymers are designed and synthesized by grafting the TADF emitter to the side chain of the polycarbazole backbone. By employing these TADF polymers with large ratio of delayed fluorescence component and high photoluminescence quantum yield as the emitters, the solution-processed light-emitting diodes achieve a maximal external quantum efficiency of 16.1% at a luminance of around 100 cd m-2 .

Side-Chain Effects on Energy-Level Modulation and Device Performance of Organic Semiconductor Acceptors in Organic Solar Cells.

Two new non-fullerene acceptors, IDTC and IDTO, were designed and synthesized for the application in organic solar cells (OSCs). Compared with IDTC, the introduction of electron-donating alkoxy groups of IDTO leads to a higher LUMO level with a slightly blue-shifted absorption. Using the polymer PBDB-T as donor and the two small molecules as acceptors in the conventional device structure, the IDTC-based OSC exhibits a power conversion efficiency (PCE) of 9.35% with an open-circuit voltage (VOC) of 0.917 V, a short-circuit current density (JSC) of 16.56 mA cm-2, and a fill factor (FF) of 61.61%. For the OSC based on IDTO, a higher PCE of 10.02% with a VOC of 0.943 V, a JSC of 16.25 mA cm-2, and an FF of 65.41% are obtained. The more balanced µe/µh, evident aggregation, and phase separation contribute to the higher FF for the device based on IDTO. The increased JSC for the device based on PBDB-T:IDTC can be attributed to the red-shifted and stronger absorption of the PBDB-T:IDTC blend film. These results indicate fine-tuning the electronic energy and absorption of non-fullerene acceptors is feasible to improve the performance of OSCs.

Dendronized delayed fluorescence emitters for non-doped, solution-processed organic light-emitting diodes with high efficiency and low efficiency roll-off simultaneously: two parallel emissive channels.

We have developed two new carbazole-dendronized emitters based on a green emissive thermally activated delayed fluorescence (TADF) core. Both dendrimers possess excellent thermal stability, good solution processability, and an obvious TADF feature. Non-doped OLEDs based on the emitters formed by a solution process exhibit a maximum external quantum efficiency (EQE) of 13.8%. Remarkably, the EQE remains as high as 13.3% at the high luminance of 1000 cd m-2. To the best of our knowledge, this is one of the highest EQE values for dendrimer-based fluorescent OLEDs, which nearly harvest all of the generated excitons and exhibit a considerably low loss of EQE estimated from 1000 to 5000 cd m-2. Furthermore, we reveal a new emissive approach to utilize the excitons by a combination of both TADF and exciplex emission.

Dithieno[3,2-b:2',3'-d]pyridin-5(4H)-one based D-A type copolymers with wide bandgaps of up to 2.05 eV to achieve solar cell efficiencies of up to 7.33.

Two new polymers, PDTPO-IDT and PDTPO-IDTT, are synthesized through copolymerization of 4-(2-octyldodecyl)-dithieno[3,2-b:2',3'-d]pyridin-5(4H)-one (DTPO) with indacenodithiophene (IDT) or indacenodithieno[3,2-b]thiophene (IDTT). The rational combination of the planar DTPO unit with ladder-type IDT and IDTT units endows the resulting copolymers with wide optical bandgaps of ca. 2.05 eV, low HOMO energy levels of ca. -5.32 eV and good hole-transporting abilities with a hole mobility of 1.0 × 10-3 cm2 V-1 s-1. The polymer solar cell (PSC) in a conventional structure based on PDTPO-IDT as donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor achieves a high power conversion efficiency (PCE) of up to 7.33%, the highest value for PSCs based on polymers with optical bandgap over 2.0 eV to date, along with a remarkable open-circuit voltage (Voc) approaching 0.97 V. The performance of the PDTPO-IDTT based PSC is slightly behind this with a moderate PCE of 5.47% under the same conditions. The relationship between the copolymer structures and optoelectronic properties as well as photovoltaic performance are comprehensively investigated by experiments and theoretical simulations.