Extended Conjugation Strategy Enabling Red-Shifted and Efficient Emission of Orange-Red Thermally Activated Delayed Fluorescence Materials.

In account of the energy gap law, the development of efficient narrow-band gap thermally activated delayed fluorescence (TADF) materials remains a major challenge for the application of organic light-emitting diodes (OLEDs). The orange-red TADF materials are commonly designed with either large π-conjugated systems or strong intramolecular donor-acceptor (D-A) interactions for red-shift emission and small singlet-triplet energy gap (ΔEST). There are rare reports on the simultaneous incorporation of these two strategies on the same material systems. Herein, two orange-red emitters named 1P2D-BP and 2P2D-DQ have been designed by extending the conjugation degree of the center acceptor DQ and increasing the number distribution of the peripheral donor PXZ units, respectively. The emission peak of 1P2D-BP is red-shifted to 615 nm compared to 580 nm for 2P2D-DQ, revealing the pronounced effect of the conjugation extension on the emission band gap. In addition, the distorted molecular structure yields a small ΔEST of 0.02 eV, favoring the acquisition of a high exciton utilization through an efficient reverse intersystem crossing process. As a result, orange-red OLEDs with both 1P2D-BP and 2P2D-DQ have achieved an external quantum efficiency (EQE) of more than 17%. In addition, the efficient white OLED based on 1P2D-BP is realized through precise exciton assignment and energy transport modulation, showing an EQE of 23.6% and a color rendering index of 82. The present work provides an important reference for the design of high-efficiency narrow-band gap materials in the field of solid-state lighting.

Constructing π-π Superposition Effect of Tetralithium Naphthalenetetracarboxylate with Electron Delocalization for Robust Dual-Ion Batteries.

Organics are gaining significance as electrode materials due to their merits of multi-electron reaction sites, flexible rearrangeable structures and redox reversibility. However, organics encounter finite electronic conductivity and inferior durability especially in organic electrolytes. To circumvent above barriers, we propose a novel design strategy, constructing conductive network structures with extended π-π superposition effect by manipulating intermolecular interaction. Tetralithium 1,4,5,8-naphthalenetetracarboxylate (LNTC) interwoven by carbon nanotubes (CNTs) forms LNTC@CNTs composite firstly for Li-ion storage, where multiple conjugated carboxyls contribute sufficient Li-ion storage sites, the unique network feature enables electrolyte and charge mobility conveniently combining electron delocalization in π-conjugated system, and the enhanced π-π superposition effect between LNTC and CNTs endows laudable structural robustness. Accordingly, LNTC@CNTs maintain an excellent Li-ion storage capacity retention of 96.4 % after 400 cycles. Electrochemical experiments and theoretical simulations elucidate the fast reaction kinetics and reversible Li-ion storage stability owing to the electron delocalization and π-π superposition effect, while conjugated carboxyls are reversibly rearranged into enolates during charging/discharging. Consequently, a dual-ion battery combining this composite anode and expanded graphite cathode exhibits a peak specific capacity of 122 mAh g-1 and long cycling life with a capacity retention of 84.2 % after 900 cycles.

The structure of anthocyanins and the copigmentation by common micromolecular copigments: A review.

Under natural physiological conditions, anthocyanins can keep bright and stable color for a long time due to the relatively stable acid-base environment of plant vacuoles and the copigmentation from various copigment substances, such as polyphenols, nucleotides, metallic ions and other substances. Therefore, the copigmentation caused by copigments is considered an effective way to stabilize anthocyanins against adverse environmental conditions. This is attributed to the covalent and noncovalent interactions between colored forms of anthocyanins (flavylium ions and quinoidal bases) and colorless or pale yellow organic molecules (copigments). These interactions are usually manifested in both hyperchromic effect and bathochromic shifts. In addition to making anthocyanins more stable, the copigmentation also could make an important contribution to the diversification of their tone. Based on the molecular structure of anthocyanins, this review focuses on the interaction mode of auxochrome groups or copigments with anthocyanins and their effects on the chemical and color stability of anthocyanins.

Modeling the extent of conjugation in histochemical dyes and fluorescent probes: clarification in calculating conjugated bond number (CBN) and introduction of a new parameter, resonance energy.

Determining the extent of conjugation in dyes and fluorochromes is a helpful tool for understanding or predicting the behavior of these compounds when used as stains for microscopy. One measure that has been used repeatedly is conjugated bond number (CBN), which is the number of bonds in a conjugated system. CBN can be obtained by inspection of the structure of a compound, but the rules for how to determine what constitutes a conjugated system are not fully established. Using molecular modeling software, we have defined more clearly which groups contribute to conjugation and which do not. We accomplished this by using a new parameter, resonance energy (RE'), which is the energy differential between a conjugated compound and its unconjugated counterpart. Conjugated compounds possess less energy. If a compound contains a questionable atom or group, RE' can be calculated for the compound with and without that group. If RE' is the same for both, the group in question plays no role in the resonance and thus is not part of the conjugated system.

Extending the π-Conjugated System in Spiro-Type Hole Transport Material Enhances the Efficiency and Stability of Perovskite Solar Modules.

Hole transport materials (HTMs) are a key component of perovskite solar cells (PSCs). The small molecular 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl)-amine-9,9'-spirobifluorene (spiro-OMeTAD, termed "Spiro") is the most successful HTM used in PSCs, but its versatility is imperfect. To improve its performance, we developed a novel spiro-type HTM (termed "DP") by substituting four anisole units on Spiro with 4-methoxybiphenyl moieties. By extending the π-conjugation of Spiro in this way, the HOMO level of the HTM matches well with the perovskite valence band, enhancing hole mobility and increasing the glass transition temperature. DP-based PSC achieves high power conversion efficiencies (PCEs) of 25.24 % for small-area (0.06 cm2 ) devices and 21.86 % for modules (designated area of 27.56 cm2 ), along with the certified efficiency of 21.78 % on a designated area of 27.86 cm2 . The encapsulated DP-based devices maintain 95.1 % of the initial performance under ISOS-L-1 conditions after 2560 hours and 87 % at the ISOS-L-3 conditions over 600 hours.

Meroterpenoids with a large conjugated system from Ganoderma lucidum and their inhibitory activities against renal fibrosis.

Baoslingzhines A-E (1-5), five new meroterpenoids were isolated from the fruiting bodies of Ganoderma lucidum. The structures including their absolute configurations were characterized by using spectroscopic and computational methods. Compound 1 is a novel trinormeroterpenoid featuring the presence of an unusual dihydronaphthalene representing an unprecedented meroterpenoid skeleton. Compounds 2-4 are mononormeroterpenoids characteristic of a large conjugated system. Among them, racemic 3 and 4 were separated by HPLC on chiral phase. Biological evaluation toward kidney fibrosis found that compounds 2 and (+)-3 could inhibit the expression of fibronectin and collagen I dose dependently in TGF-ß1-induced rat kidney proximal tubular cells (NRK-52e). Additionally, (+)-3 could also down regulate ɑ-SMA in a concentration dependent manner. Further investigation showed that 2 could inhibit Smad2 phosphorylation.

π-Conjugated molecules identified for reversible and visual detection of F- in aqueous: Effect of heterocycle unit on sensing performance.

To illustrate the impact of molecular structure, especially heterocycle unit, on the sensing performance, two kinds of π-conjugated molecules containing aromatic heterocyclic (Dye 1) and aromatic ring (Dye 2) were identified and compared each other. Even with similar structures, they possessed quite different spectral and colorimetric responses to F-, Cl-, Br-, I-, NO3-, HSO4-, H2PO4-, ClO4- and CH3COO-, etc. The reason might result from the difference in withdraw-electron ability of aromatic and heterocyclic rings, which would lead to different acidity of active H in the target π-conjugated molecules. In acidic aqueous, Dye 1 expressed a reversible ratiometric-colorimetric response to F-, accompanying with a visual color change from bright yellow to purple, a nice linear range of 2.0-35.0 × 10-6 mol/L and a low detection limit of 1.60 × 10-7 mol/L. While Dye 2 did not react with any anion due to its weak acidity of active hydrogen. Under the optimized conditions, Dye 1 was successfully applied for colorimetric or naked-eye detection of F- in environmental water, tea and toothpaste samples with RSD ≤ 3.1%. The recognition mechanism for Dye 1 to F- was confirmed to be deprotonation one with a 1:1 binding stoichiometry.

Conjugated System of PEDOT:PSS-Induced Self-Doped PANI for Flexible Zinc-Ion Batteries with Enhanced Capacity and Cyclability.

Owing to its electronic conductivity and electrochemical reactivity, polyaniline (PANI) can serve as the cathode for rechargeable zinc-ion batteries (ZIBs). However, it suffers from fast deactivation and thus performance deterioration because of spontaneous deprotonation during charge/discharge. Here, we report an effective strategy to improve the electrochemical reactivity and stability of the PANI-based cathode by constructing a π-electron conjugated system between PANI and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on carbon nanotubes (CNTs). The impressive performance of the post-treated CNTs-PANI-PEDOT:PSS (t-CNTs-PA-PE) cathode is largely attributed to the -SO3-H+ groups in PSS, which acts as an internal proton reservoir and provides enough H+ for PANI's protonation, thus promoting its electrochemical activity and reversibility. Besides, the strong interactions between PANI and PEDOT:PSS assist the stretching of π-π conjugation chains, bringing about enhanced electronic conductivity. Consequently, the t-CNTs-PA-PE cathode achieves a high capacity of 238 mA h g-1, together with good rate capability and long-term stability (over 1500 cycles with 100% Coulombic efficiency). Through exerting the freestanding t-CNTs-PA-PE, a flexible ZIB was further constructed with both outstanding electrochemical properties and superior high safety. This work demonstrates the availability of conducting polymer cathodes for high-performance ZIBs, fulfilling the need of flexible electronics.

Selective Synthesis and Properties of Electron-Deficient Hybrid Naphthalene-Based π-Conjugated Systems.

One driving force for advancing the field of semiconducting polymers is to create new π-conjugated systems as building units. This work reports on a series of electron-deficient hybrid naphthalene-based π-conjugated systems in which two different units among benzoxadiazole, benzothiadiazole, benzoselenadiazole, and benzopyrazine (quinoxaline) were fused. These π-conjugated systems were synthesized in excellent yields via the selective one-side ring-opening reaction of corresponding naphthobischalcogenadiazoles using the NaBH4 /CoCl2 reduction reagents, followed by the ring-closing reactions. The electronic structure of these π-conjugated systems was studied in comparison with their parent systems. Furthermore, thiadiazolonaphthoxadiazole was incorporated into the π-conjugated polymer backbone. The electronic structure, film structure, and photovoltaic properties of the polymer were studied as well.

EQE Climbing Over 6% at High Brightness of 14350 cd/m2 in Deep-Blue OLEDs Based on Hybridized Local and Charge-Transfer Fluorescence.

Three deep-blue emitters PPi-Pid, PPi-Xid, and PPi-Mid based on a novel conjugated system phenantroimidazole-π-indolizine have been designed and synthesized. Here, indolizine with appropriate π-conjugation length was used as the acceptor profited from its high-photoluminescence quantum yield and good electron-withdrawing ability. Fluorescent organic light-emitting diodes (OLEDs) based on PPi-Pid, PPi-Xid, and PPi-Mid achieved deep-blue emissions with the Commission Internationale de L'Eclairage coordinates of (0.151, 0.076), (0.155, 0.052), and (0.153, 0.052); high brightness of 14350, 4377, and 4002 cd/m2; and high external quantum efficiencies (EQEs) of 6.01, 3.90, and 4.28%, respectively. Moreover, it is noticeable that all of the devices exhibited efficiencies increasing with brightness. In particular, the PPi-Pid-based device exhibited high EQE over 6% at a high brightness of 14350 cd/m2. Such high brightness along with high EQE is very rare whether in deep-blue fluorescent or thermally activated delayed fluorescent OLEDs.

Anti-wrinkle and UV protective performance of cotton fabrics finished with 5-(carbonyloxy succinic)-benzene-1,2,4-tricarboxylic acid.

1,2,3,4-Butane tetracarboxylic acid (BTCA) has been considered as one of the most promising crosslinking agent to replace dimethylol dihydroxy ethylene urea (DMDHEU) for anti-wrinkle finishing on cotton fabrics. However, it could cause significant strength loss of the treated fabrics. In this study, a 5-(carbonyloxy succinic)-benzene-1,2,4-tricarboxylic acid (BSTA) was synthesized and applied as an effective crosslinking agent. The results show that fabrics treated with BSTA present the same or even better anti-wrinkle properties as that with BTCA. FTIR was employed to analyze ester bond formation process on cellulose. Finishing conditions such as agent concentration, curing temperature, and bath pH were also discussed to evaluate crosslinking effect of cellulose. BSTA, as a derivative of photo-active conjugated compound, can absorb ultraviolet lights and offer ultraviolet (UV) protective property on treated materials. The treated fabrics showed excellent UV protection performance due to the addition of aromatic conjugated system on fabrics.

Pyrene-Bridged Boron Subphthalocyanine Dimers: Combination of Planar and Bowl-Shaped π-Conjugated Systems for Creating Uniquely Curved π-Conjugated Systems.

Pyrene-bridged boron subphthalocyanine dimers were synthesized from a mixed-condensation reaction of 2,7-di-tert-butyl-4,5,9,10-tetracyanopyrene and tetrafluorophthalonitrile, and their syn and anti isomers arising from the result of connecting two bowl-shaped boron subphthalocyanine molecules were successfully separated. Expansion of the conjugated system of boron subphthalocyanine through a pyrene bridge caused a redshift of the Q band absorption relative to the parent pyrene-fused monomer, whereas combining the curved π-conjugation of boron subphthalocyanine with the planar π-conjugation of pyrene enabled facile embracement of C60 molecules, owing to the enhanced concave-convex π-π stacking interactions.

Palladium-Catalyzed Construction of Heteroatom-Containing π-Conjugated Systems by Intramolecular Oxidative C-H/C-H Coupling Reaction.

Synthesis of heteroatom-containing ladder-type π-conjugated molecules was successfully achieved via a palladium-catalyzed intramolecular oxidative C-H/C-H cross-coupling reaction. This reaction provides a variety of π-conjugated molecules bearing heteroatoms, such as nitrogen, oxygen, phosphorus, and sulfur atoms, and a carbonyl group. The π-conjugated molecules were synthesized efficiently, even in gram scale, and larger π-conjugated molecules were also obtained by a double C-H/C-H cross-coupling reaction and successive oxidative cycloaromatization.

Nanoporous carbon tubes from fullerene crystals as the π-electron carbon source.

Here we report the thermal conversion of one-dimensional (1D) fullerene (C60) single-crystal nanorods and nanotubes to nanoporous carbon materials with retention of the initial 1D morphology. The 1D C60 crystals are heated directly at very high temperature (up to 2000 °C) in vacuum, yielding a new family of nanoporous carbons having π-electron conjugation within the sp(2)-carbon robust frameworks. These new nanoporous carbon materials show excellent electrochemical capacitance and superior sensing properties for aromatic compounds compared to commercial activated carbons.