A brand-new type of excited-state proton transfer (ESIPT) molecule based on sulfoxide/sulfenic acid tautomerism.

The excited-state proton transfer (ESIPT) behavior of organic fluorophores has attracted much attention due to their unique photophysical properties. So far, ESIPT studies have mainly focused on the transfer of hydrogen atoms between N-N, N-O, or O-O. In this work, a brand-new type of ESIPT molecule based on sulfoxide/sulfenic acid tautomerism has been thoroughly investigated. The sulfoxide/sulfenic acid tautomerization process requires one step and two steps in the ground and first excited singlet states, respectively. A range of density functional theory and time-dependent density functional theory methods have been employed to investigate these structures, and the changes in aromaticity may be responsible for obtaining the ESIPT process. This work presents a novel ESIPT process, showcasing molecules that exhibit distinctive properties compared to conventional ESIPT compounds. These findings are expected to expand the horizons of experimental research in ESIPT.

Regioselective synthesis of 3-nitroindoles under non-acidic and non-metallic conditions.

An electrophilic substitution reaction, without acid and metal, of indole with ammonium tetramethylnitrate for accessing 3-nitroindole has been developed. In this protocol, trifluoroacetyl nitrate (CF3COONO2) was produced by metathesis of ammonium tetramethyl nitrate and trifluoroacetic anhydride at sub-room temperature. Trifluoroacetyl nitrate (CF3COONO2) is an electrophilic nitrating agent for a variety of indoles, aromatic and heterocyclic aromaticity. Meanwhile, this strategy could be applied to construct the skeleton structure of many kinds of bioactive molecules. Interestingly, 3-nitroindole can be further derivatived as a pyrrolo[2,3-b]indole.

Mechanically induced single-molecule white-light emission of excited-state intramolecular proton transfer (ESIPT) materials.

Described herein is the first example of mechanically induced single-molecule white-light emission based on excited-state intramolecular proton transfer (ESIPT) materials. The mechanism of mechanochromism is clearly disclosed by powder and single crystal X-ray diffraction (XRD) data, infrared spectroscopy, and fluorescence up-conversion measurement, etc. 2-(2'-Hydroxyphenyl)oxazole (6b) with a herringbone packing motif exhibits a predominant keto-form emission, giving off yellowish-green fluorescence. Mechanical grinding transforms the herringbone packing motif into a brickwork packing motif, decreases the intermolecular distances, which results in an enhanced intermolecular charge-transfer interaction, and therefore changes the ESIPT dynamics, leading to an enhanced enol-form emission and white fluorescence. Herringbone-packing 6b is thermodynamically more stable than brickwork-packing 6b. Thus, the latter can convert to the former by solvent fuming or thermal annealing.

A methyl-shield strategy enables efficient blue thermally activated delayed fluorescence hosts for high-performance fluorescent OLEDs.

Here, we report a novel methyl-shield strategy to design ideal TADF hosts for the improvement of the performance of TSF-OLEDs. The methyl group on the xanthone acceptor acts like a shield to protect the luminance center from close intermolecular hydrogen bonding with adjacent molecules, thus alleviating exciton quenching, and meanwhile the small size of the methyl group almost does not disturb the π-π stacking between acceptors, thus maintaining fast electron-transport pathways. dMeACRXTO having two methyl shields is exploited as the host to achieve a record-high EQE of 32.3%, which represents the first report of an EQE above 30% in TSF-OLEDs.

"H-Type" Like Constructed Dimer: Another Way to Enhance the Thermally Activated Delayed Fluorescence Effect.

Thermally activated delayed fluorescence (TADF) materials are an essential part of TADF-based organic light-emitting diodes (OLEDs). All the reported methods to improve the performance of TADF materials were focused on achieving a high reverse intersystem crossing rate (kRISC) and oscillator strength (f), but most of them were studies on single molecular states. In this paper, we have discovered a new dimer architecture called the "H-type" like dimer and proved that the "H-type" like dimer is another way to improve the performance of TADF materials by calculation and experiment. The calculated energy levels of excited states only provided 1.72-5.46% relative errors (RE) compare with the measured values, which indicated that the methods we chose were suitable for predicting the properties. The intermolecular interactions of the "H-type" like dimer endow it with much larger f and kRISC properties than monomer states, proving that the "H-type" like dimer could improve the performance of TADF emitters.

Synthesis of Imidazole-Based [30]Heptaphyrin and Stable Figure-Eight [60]Tetradecaphyrins via [5 + 2] Condensations in One Pot.

Derived from a Pd-catalyzed oxidative C-H/C-H coupling reaction, two giant imidazole-based [60]tetradecaphyrins adopting stable figure-eight geometry together with one [30]heptaphyrin are obtained by [5 + 2] MacDonald condensations in one pot. The directional imidazole is believed to play a vital role for the diverse cyclization and conformation stabilization.

Triazolotriazine-based thermally activated delayed fluorescence materials for highly efficient fluorescent organic light-emitting diodes (TSF-OLEDs).

Thermally activated delayed fluorescence (TADF) sensitized fluorescent organic light-emitting diodes (TSF-OLEDs) have shown great potential for the realization of high efficiency with low efficiency roll-off and good color purity. However, the superior examples of TSF-OLEDs are still limited up to now. Herein, a trade-off strategy is presented for designing efficient TADF materials and achieving high-performance TSF-OLEDs via the construction of a new type of triazolotriazine (TAZTRZ) acceptor. The enhanced electron-withdrawing ability of TAZTRZ acceptor, fused by triazine (TRZ) and triazole (TAZ) together, enables TADF luminogens with small singlet-triplet energy gap (ΔEST) values. Meanwhile, the increased planarity from the TRZ-phenyl linkage (6:6 system) to the TAZ-phenyl linkage (5:6 system) can compensate the decrease of oscillator strength (f) while lowing ΔEST, thus achieving a trade-off between small ΔEST and high f. As a result, the related TSF-OLED achieved an extremely low turn-on voltage of 2.1 V, an outstanding maximum external quantum efficiency (EQEmax) of 23.7% with small efficiency roll-off (EQE1000 of 23.2%; EQE5000 of 20.6%) and an impressively high maximum power efficiency of 82.1 lm W-1, which represents the state-of-the-art performance for yellow TSF-OLEDs.

Molecular Design of Non-doped OLEDs Based on a Twisted Heptagonal Acceptor: A Delicate Balance between Rigidity and Rotatability.

The development of efficient non-doped organic light-emitting diodes (OLEDs) is highly desired but very challenging because of a severe aggregation-caused quenching effect. Herein, we present a heptagonal diimide acceptor (BPI), which can restrict excessive intramolecular rotation and inhibit close intermolecular π-π stacking due to well-balanced rigidity and rotatability of heptagonal structure. The BPI-based luminogen (DMAC-BPI) shows significant aggregation-induced delayed florescence with an extremely high photoluminescence quantum yield (95.8 %) of the neat film, and the corresponding non-doped OLEDs exhibit outstanding electroluminescence performance with maximum external quantum efficiency as high as 24.7 % and remarkably low efficiency roll-off as low as 1.0 % at 1000 cd m-2 , which represents the state-of-the-art performance for non-doped OLEDs. In addition, the synthetic route to DMAC-BPI is greatly streamlined and simplified through oxidative Ar-H/Ar-H homo-coupling reaction.

Hydrogen bond modulation in 1,10-phenanthroline derivatives for versatile electron transport materials with high thermal stability, large electron mobility and excellent n-doping ability.

4,7-Bisphenyl-1,10-phenanthroline (BPhen) is a promising electron transport material (ETM) and has been widely used in organic light-emitting diodes (OLEDs) because of the large electron mobility and easy fabrication process. However, its low glass transition temperature would lead to poor device stability. In the past decades, various attempts have been carried out to improve its thermal stability though always be accomplished by the reduced electron mobility. Here, we present a molecular engineering to modulate the properties of BPhen, and through which, a versatile BPhen derivative (4,7-bis(naphthalene-ß-yl)-1,10-phenanthroline, ß-BNPhen) with high thermal stability (glass transition temperature = 111.9 °C), large electron mobility (7.8 × 10-4 cm2/(V s) under an electrical field of 4.5 × 105 V/cm) and excellent n-doping ability with an air-stable metal of Ag is developed and used as multifunctional layers to improve the efficiency and enhance the stability of OLEDs. This work elucidates the great importance of our molecular engineering methodology and device structure optimization strategy, unlocking the potential of 1,10-phenanthroline derivatives towards practical applications.

Build-up of double carbohelicenes using nitroarenes: dual role of the nitro functionality as an activating and leaving group.

The construction of double carbohelicenes is highly fascinating yet challenging work. Disclosed herein is a streamlined and simplified synthetic route to double carbohelicenes starting from nitroarenes through sequential nitro-activated ortho-C-H arylation, denitrative alkenylation and intramolecular cyclodehydrogenation. In this synthetic strategy, the nitro group plays a dual role namely as a leaving group for the denitrative alkenylation and as an activating group for ortho-C-H arylation, which is distinct from those of aryl halides in a conventional coupling reaction. In this work, the palladium-catalyzed Heck-type alkenylation of nitroarenes has been presented, in which the conventionally inert Ar-NO2 bond is cleaved. This work provides a novel synthetic strategy for polycyclic aromatic hydrocarbons (PAHs).

An unusual [4 + 2] fusion strategy to forge meso-N/O-heteroarene-fused (quinoidal) porphyrins with intense near-infrared Q-bands.

Here we present a divergent synthesis of brand-new types of meso-N/O-heteroarene-fused (quinoidal) porphyrins through Rh-catalyzed ß-C-H activation/annulation of 5,15-dioxoporphyrins and dioxime derivatives with alkynes, in which the synthetic disconnections are difficult to access through the commonly used intramolecular cyclization strategy. Using the O-methyl oxime as a traceless oxidizing directing group, the meso-N-embedded pyridine-fused anti-quinoidal porphyrin 3 and pyridinium-fused cation 4 are formed with controllable chemoselectivity and complete anti-selectivity. Replacing the exocyclic oxime with a carbonyl group delivers the pyran-fused porphyrin 5, achieving structural conversion from a quinoidal conformation to a stable porphyrin macrocycle. Further oxidation of the expanded dimer 5ea gives the oxonium 6, which exhibits intense near-infrared (NIR) Q-bands up to 1300 nm. Theoretical studies demonstrate that the incorporation of a heteroatom at the meso-position enables more effective π-extension, resulting in a 22π aromatic (vs. 18π aromatic) character of pyran-fused porphyrins (syn/anti-5aa). Compared with the commercially available methylene blue (MB), syn-5al exhibits a better ability (Φ Δ = 0.61) to sensitize singlet oxygen (1O2) when irradiated with a 680 nm laser beam, and has potential as a photodynamic therapy (PDT) photosensitizer in the body's therapeutic window (650-900 nm).

Making silver a stronger n-dopant than cesium via in situ coordination reaction for organic electronics.

N-doping is an effective way to increase the electron conductivity of organic semiconductors and achieve ohmic cathode contacts in organic electronics. To avoid the use of difficult-to-handle highly reactive n-dopants, air-stable precursors are widely used nowadays, which could decompose to release reactive species in a subtractive way though always with unwanted and even harmful byproducts during processing. Here, we show that air-stable metals, such as copper, silver and gold, could release free electrons readily in the presence of chelating ligands, as the irreversible coordination reaction between metal ions and the ligands would push the equilibrium between metals and metal ions to the forward direction. By using a well-designed multi-functional electron transport material with a strong nucleophilic quality, 4,7-dimethoxy-1,10-phenanthroline (p-MeO-Phen), silver could function as an n-dopant stronger than cesium and could be used to fabricate organic light-emitting diodes with higher performance than the cesium-doped control device.

Synthesis of a Double-Helical Naphthotetraindole Core via an Intramolecular Dehydrogenative Homocoupling Reaction.

A novel naphthotetraindole (NTI) core was synthesized in two steps via the McMurry reaction and a [Cu]/[Ag]-promoted intramolecular dehydrogenative homocoupling reaction. NTI shows a unique X-shaped double-helical structure as determined by single-crystal X-ray diffraction analysis. The hole-transport mobility of the bare NTI core was measured to be 2.3 × 10-5 cm2 V-1 s-1, which is comparable with the commonly used Spiro-OMeTAD.

Zn(II)-dipicolylamine-based metallo-lipids as novel non-viral gene vectors.

In this study, a series of Zn(II)-dipicolylamine (Zn-DPA) based cationic lipids bearing different hydrophobic tails (long chains, α-tocopherol, cholesterol or diosgenin) were synthesized. Structure-activity relationship (SAR) of these lipids was studied in detail by investigating the effects of several structural aspects including the type of hydrophobic tails, the chain length and saturation degree. In addition, several assays were used to study their interactions with plasmid DNA, and results reveal that these lipids could condense DNA into nanosized particles with appropriate size and zeta-potentials. MTT-based cell viability assays showed that lipoplexes 5 had low cytotoxicity. The in vitro gene transfection studies showed the hydrophobic tails clearly affected the TE, and hexadecanol-containing lipid 5b gives the best TE, which was 2.2 times higher than bPEI 25k in the presence of 10% serum. The results not only demonstrate that these lipids might be promising non-viral gene vectors, but also afford us clues for further optimization of lipidic gene delivery materials.

Biodegradable Poly(Amino Ester) with Aromatic Backbone as Efficient Nonviral Gene Delivery Vectors.

The development of gene delivery vectors with high efficiency and biocompatibility is one of the critical points of gene therapy. Two biodegradable poly(amino ester)s were synthesized via ring-opening polymerization between low molecular weight (LMW) PEI and diepoxide. The molecular weights of poly(amino ester)s were measured by GPC. Agarose gel retardation assays showed that these materials have good DNA-binding ability and can retard the electrophoretic mobility of plasmid DNA (pDNA) at a weight ratio of 1. The formed polyplexes have proper sizes of around 200 nm and zeta-potential values of about 30-40 mV for cellular uptake. In vitro experiments revealed that polymer P2 gave higher transfection efficiency than PEI 25KDa and Lipofectamine 2000 with less toxicity, especially in 293 cells. Results demonstrate that such a type of degradable poly(amino ester) may serve as a promising non-viral gene vector.

pH and reduction dual-responsive dipeptide cationic lipids with α-tocopherol hydrophobic tail for efficient gene delivery.

A series of tocopherol-based cationic lipid 3a-3f bearing a pH-sensitive imidazole moiety in the dipeptide headgroup and a reduction-responsive disulfide linkage were designed and synthesized. Acid-base titration of these lipids showed good buffering capacities. The liposomes formed from 3 and co-lipid 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) could efficiently bind and condense DNA into nanoparticles. Gel binding and HPLC assays confirmed the encapsulated DNA could release from lipoplexes 3 upon addition of 10 mM glutathione (GSH). MTT assays in HEK 293 cells demonstrated that lipoplexes 3 had low cytotoxicity. The in vitro gene transfection studies showed cationic dipeptide headgroups clearly affected the transfection efficiency (TE), and arginine-histidine based dipeptide lipid 3f give the best TE, which was 30.4 times higher than Lipofectamine 3000 in the presence of 10% serum. Cell-uptake assays indicated that basic amino acid containing dipeptide cationic lipids exhibited more efficient cell uptake than serine and aromatic amino acids based dipeptide lipids. Confocal laser scanning microscopy (CLSM) studies corroborated that 3 could efficiently deliver and release DNA into the nuclei of HeLa cells. These results suggest that tocopherol-based dipeptide cationic lipids with pH and reduction dual-sensitive characteristics might be promising non-viral gene delivery vectors.

Lipoic acid functionalized amino acids cationic lipids as gene vectors.

A series of reducible cationic lipids 4a-4f with different amino acid polar-head groups were prepared. The novel lipid contains a hydrophobic lipoic acid (LA) moiety, which can be reduced under reductive conditions to release of the encapsulated plasmid DNA. The particle size, zeta potential and cellular uptake of lipoplexes formed with DNA, as well as the transfection efficacy (TE) were characterized. The TE of the cationic lipid based on arginine was especially high, and was 2.5times higher than that of a branched polyethylenimine in the presence of 10% serum.

Reducible Amino Acid Based Cationic Lipids as Highly Efficient and Serum-Tolerant Gene Vectors.

In this study, two cationic lipids, each containing an α-tocopherol moiety and a biocompatible amino acid headgroup (histidine or lysine) linked through a biodegradable disulfide and carbamate bond, were prepared and evaluated in cell culture as nonviral gene delivery vectors. The physicochemical properties of these lipids, including size, zeta potential and cellular uptake of the lipoplexes formed with DNA, as well as the transfection efficacy (TE), were investigated. The results show that the chemical structure of the cationic headgroup affects the physicochemical parameters of these amino acid based lipids and especially the TE. In addition to their low cytotoxicity, these lipoplexes also showed comparable TE with the commercially available Lipofectamine 2000. The TE of the cationic lipid based on histidine was especially high, and was 4.3 times higher than that of a branched polyethylenimine in the presence of 10 % serum. These results demonstrate the promise of amino acid based lipids for safe and efficient gene delivery.

Charge-switching amino acids-based cationic lipids for efficient gene delivery.

A series of charge-switching amino acids-based cationic lipids 4a-4e bearing a benzyl ester at the terminus of the acyl chain, but differing in the polar-head group were prepared. The physicochemical properties of these lipids, including size, zeta potential and cellular uptake of the lipoplexes formed from with DNA, as well as the transfection efficiency (TE), were investigated. The results showed that the chemical structure of the cationic head-group clearly affects the physicochemical parameters of the amino acid-based lipids and especially the TE. The selected lipid, 4c gave 2.1 times higher TE than bPEI 25k in the presence of 10% serum in HeLa cells, with little toxicity.

Amino acid-based cationic lipids with α-tocopherol hydrophobic tail for efficient gene delivery.

In this work, three amino acid-based cationic lipids L1-L3 bearing the same α-tocopherol moiety and biodegradable ester bond linkage, but differing in the polar head-group, were prepared and applied as non-viral gene delivery vectors. The physicochemical properties such as size, zeta-potential, stability, and cellular uptake of the lipoplexes formed from lipids L1-L3 as well as the transfection efficacy (TE) were investigated. The results showed that the chemical composition of the cationic head-group clearly affects the physicochemical parameters of the amino acid-based lipids, especially the TE. Besides their low cytotoxicity, these lipoplexes also showed comparable TE to commercially available lipofectamine 2000. In particular, dipeptide lipid L3 gave excellent TE, which was 1.8 times higher than bPEI 25k in the presence of 10% serum in Hela cells. These results demonstrate the promising use of novel dipeptide lipids for safe and efficient gene delivery.