Unraveling non-radiative decay channels of exciplexes to construct efficient red emitters for organic light-emitting diodes.

Exciplex emitters naturally have thermally activated delayed fluorescence characteristics due to their spatially separated molecular orbitals. However, the intermolecular charge transfer potentially induces diverse non-radiative decay channels, severely hindering the construction of efficient red exciplexes. Thus, a thorough comprehension of this energy loss is of paramount importance. Herein, different factors, including molecular rigidity, donor-acceptor interactions and donor-donor/acceptor-acceptor interactions, that impact the non-radiative decay were systematically investigated using contrasting exciplex emitters. The exciplex with rigid components and intermolecular hydrogen bonds showed a photoluminescence quantum yield of 84.1% and a singlet non-radiative decay rate of 1.98 × 106 s-1 at an optimized mixing ratio, respectively, achieving a 3.3-fold increase and a 70% decrease compared to the comparison group. In the electroluminescent device, a maximum external quantum efficiency of 23.8% was achieved with an emission peak of 608 nm, which represents the state-of-the-art organic light-emitting diodes using exciplex emitters. Accordingly, a new strategy is finally proposed, exploiting system rigidification to construct efficient red exciplex emitters that suppress non-radiative decay.

KDM1A, a potent and selective target, for the treatment of DNMT3A-deficient non-small cell lung cancer.

BACKGROUND: DNMT3A is a crucial epigenetic regulation enzyme. However, due to its heterogeneous nature and frequent mutation in various cancers, the role of DNMT3A remains controversial. Here, we determine the role of DNMT3A in non-small cell lung cancer (NSCLC) to identify potential treatment strategies. METHODS: To investigate the role of loss-of-function mutations of DNMT3A in NSCLC, CRISPR/Cas9 was used to induce DNMT3A-inactivating mutations. Epigenetic inhibitor library was screened to find the synthetic lethal partner of DNMT3A. Both pharmacological inhibitors and gene manipulation were used to evaluate the synthetic lethal efficacy of DNMT3A/KDM1A in vitro and in vivo. Lastly, MS-PCR, ChIP-qPCR, dual luciferase reporter gene assay and clinical sample analysis were applied to elucidate the regulation mechanism of synthetic lethal interaction. RESULTS: We identified DNMT3A is a tumour suppressor gene in NSCLC and KDM1A as a synthetic lethal partner of DNMT3A deletion. Both chemical KDM1A inhibitors and gene manipulation can selectively reduce the viability of DNMT3A-KO cells through inducing cell apoptosis in vitro and in vivo. We clarified that the synthetic lethality is not only limited to the death mode, but also involved into tumour metastasis. Mechanistically, DNMT3A deficiency induces KDM1A upregulation through reducing the methylation status of the KDM1A promoter and analysis of clinical samples indicated that DNMT3A expression was negatively correlated with KDM1A level. CONCLUSION: Our results provide new insight into the role of DNMT3A in NSCLC and elucidate the mechanism of synthetic lethal interaction between KDM1A and DNMT3A, which might represent a promising approach for treating patients with DNMT3A-deficient tumours.

Spin characteristics in conjugated stable diradicals.

Spin properties are intrinsic characters of electrons. Radical molecules contain unpaired electron(s), and their unique chemical and physical properties make them an ideal platform for investigating spin properties in molecular systems. Among them, the burgeoning interest in stable conjugated diradicals is attributed to their distinctive characteristics, notably the dynamic resonance structures between open-shell and closed-shell forms, the malleability of their spin states, and the profound influence of intermolecular spin-spin interactions. A deep understanding of the spin characteristics of unpaired electrons in stable conjugated diradicals provides guidance for the design, synthesis, and characterization of radical-based materials. In this review, we discuss the unique spin delocalization, spin states, and spin-spin coupling characteristics of conjugated diradicals and emphasize how to precisely control these spin characteristics to understand their role in the molecules and as functional radical materials.

Neutral and Anion Species of Quinoidal Thienothiophene Diketopyrrolopyrroles Display a Common Aggregation Mode.

A comprehensive investigation of two new molecular triads incorporating the diketopyrrolopyrrole unit into a quinoidized thienothiophene skeleton, which is further end-capped with dicyanomethylene (DPP-TT-CN) or phenoxyl groups (DPP-TT-PhO), has been carried out. A combination of UV-Vis-NIR and infrared spectroelectrochemical techniques and cryogenic UV-Vis-NIR absorption spectroscopy supported by theoretical calculations has been used. The main result is the formation of similar H-aggregates in the dimerization process of the neutral molecules and of the charged anionic species. The experimental absorption spectra of the aggregated species are accurately reproduced by quantum chemical calculations using the Spano's model, including excitonic coupling for the dimeric forms and full vibronic resolution of the absorption bands. The strong excitonic coupling taking place is key to understand the electronic structure of the dimeric aggregates and has been instrumental to disentangle the type of H-aggregation. This study is of relevance to get a better understanding of the molecular aggregation of organic p-conjugated chromophores and is useful as a guideline for the refinement of the engineering of molecular materials for which supramolecular design is required.

Not in black or white, encryption of grayscale images by donor-acceptor Stenhouse adducts.

Invisible inks have been applied for the secrecy of texts, symbols and binary images. Based on the photochromism of donor-acceptor Stenhouse adducts (DASAs) in the solid-state promoted by ester-containing molecules, we report the encryption of grayscale information by controlling the kinetics of photoisomerization.

77 % Photothermal Conversion in Blatter-Type Diradicals: Photophysics and Photodynamic Applications.

Diradicals based on the Blatter units and connected by acetylene and alkene spacers have been prepared. All the molecules show sizably large diradical character and low energy singlet-triplet gaps. Their photo-physical properties concerning their lowest energy excited state have been studied in detail by steady-state and time-resolved absorption spectroscopy. We have fully identified the main optical absorption band and full absence of emission from the lowest energy excited state. A computational study has been also carried out that has helped to identify the presence of a conical intersection between the lowest energy excited state and the ground state which produces a highly efficient light-to-heat conversion of the absorbed radiation. Furthermore, an outstanding photo-thermal conversion 77.23 % has been confirmed, close to the highest in the diradicaloid field. For the first time, stable diradicals are applied to photo-thermal therapy of tumor cells with good stability and satisfactory performance at near-infrared region.

A Single-Crystal Monomer to Single-Crystal Polymer Reaction Activated by a Triplet Excimer in a Zipper Mechanism.

A combined experimental and theoretical study focused on the elucidation of the polymerization mechanism of the crystal monomer to crystal polymer reaction of a bisindenedione compound in the solid state. The experimental description and characterization of the polymer product have been reported elsewhere and, in this article, we address the first detailed description of the polymerization process. This reaction pathway consists of the initial formation of a triplet excimer state that relaxes to an intermolecularly bonded triplet state that is the starting point of the propagation step of the polymerization. The overall process can be visualized in the monomer starting state as an open zipper in which a cursor or slider is formed by light absorption and the whole zipper is then closed by propagation of the cursor. To this end, variable-temperature electron spin resonance (ESR), femtosecond transient absorption spectroscopy, and vibrational Raman spectroscopic data have been implemented in combination with quantum chemical calculations. The presented mechanistic insight is of great value to understand the intricacies of such an important reaction and to envisage and diversify the products produced thereof.

Quasi-Free Electron States Responsible for Single-Molecule Conductance Enhancement in Stable Radical.

Stable organic radicals, which possess half-filled orbitals in the vicinity of the Fermi energy, are promising candidates for electronic devices. In this Letter, using a combination of scanning-tunneling-microscopy-based break junction (STM-BJ) experiments and quantum transport theory, a stable fluorene-based radical is investigated. We demonstrate that the transport properties of a series of fluorene derivatives can be tuned by controlling the degree of localization of certain orbitals. More specifically, radical 36-FR has a delocalized half-filled orbital resulting in Breit-Wigner resonances, leading to an unprecedented conductance enhancement of 2 orders of magnitude larger than the neutral nonradical counterpart (36-FOH). In other words, conversion from a closed-shell fluorene derivative to the free radical in 36-FR opens an electron transport path which massively enhances the conductance. This new understanding of the role of radicals in single-molecule junctions opens up a novel design strategy for single-molecule-based spintronic devices.

Asymmetric and zwitterionic Blatter diradicals.

Asymmetric diradical molecular systems with different resonance mechanisms are largely unexplored. Herein, two conjugated asymmetric diradicals with Blatter and phenoxyl moieties (pBP and mBP) have been synthesized and studied in depth. A complete set of spectroscopic, X-ray crystallographic and magnetic techniques, together with quantum chemical calculations, have been used. The para-isomer (pBP) bears diradical and zwitterionic resonant forms, the latter by a electron delocalization mechanism, which are synergistically integrated by a sequence of nitrogen, provided by the Blatter moiety imine and amine (of different acceptor nature). In the meta-isomer (mBP), the zwitterionic form promoted in pBP by the lone-pair electron of the amine nitrogen is not available, yet it possesses a pseudo-hyperconjugation effect where the N lone pair mediates in a bonding coupling in a counter homolytic bond scission mechanism. Both electronic effects converge to promote medium diradical characters and narrow singlet-triplet gaps to the two electronic isomers. All these aspects delineate the subtle balance that shapes the electronic structure of open-shell molecules, which is even more challenging in the case of asymmetric systems, such as those described here with asymmetric phenoxyl-Blatter diradicals.

Controlling Isomerization of Photoswitches to Modulate 2D Logic-in-Memory Devices by Organic-Inorganic Interfacial Strategy.

Logic-in-memory devices are a promising and powerful approach to realize data processing and storage driven by electrical bias. Here, an innovative strategy is reported to achieve the multistage photomodulation of 2D logic-in-memory devices, which is realized by controlling the photoisomerization of donor-acceptor Stenhouse adducts (DASAs) on the surface of graphene. Alkyl chains with various carbon spacer lengths (n = 1, 5, 11, and 17) are introduced onto DASAs to optimize the organic-inorganic interfaces: 1) Prolonging the carbon spacers weakens the intermolecular aggregation and promotes isomerization in the solid state. 2) Too long alkyl chains induce crystallization on the surface and hinder the photoisomerization. Density functional theory calculation indicates that the photoisomerization of DASAs on the graphene surface is thermodynamically promoted by increasing the carbon spacer lengths. The 2D logic-in-memory devices are fabricated by assembling DASAs onto the surface. Green light irradiation increases the drain-source current (Ids ) of the devices, while heat triggers a reversed transfer. The multistage photomodulation is achieved by well-controlling the irradiation time and intensity. The strategy based on the dynamic control of 2D electronics by light integrates molecular programmability into the next generation of nanoelectronics.

Chemical interactions that govern the structures of metals.

Most metals adopt simple structures such as body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed (HCP) structures in specific groupings across the periodic table, and many undergo transitions to surprisingly complex structures on compression, not expected from conventional free-electron-based theories of metals. First-principles calculations have been able to reproduce many observed structures and transitions, but a unified, predictive theory that underlies this behavior is not yet in hand. Discovered by analyzing the electronic properties of metals in various lattices over a broad range of sizes and geometries, a remarkably simple theory shows that the stability of metal structures is governed by electrons occupying local interstitial orbitals and their strong chemical interactions. The theory provides a basis for understanding and predicting structures in solid compounds and alloys over a broad range of conditions.

Hydrogen-bond-induced quantum interference in single-molecule junctions of regioisomers.

Solvents can play a significant role in tuning the electrical conductance of single-molecule junctions. In this respect, protic solvents offer the potential to form hydrogen bonds with molecular backbones and induce electrostatic gating via their dipole moments. Here we demonstrate that the effect of hydrogen bond formation on conductance depends on whether transport through the junction is controlled by destructive quantum interference (DQI) or constructive quantum interference (CQI). Furthermore, we show that a protic solvent can be used to switch the conductance of single-molecule junctions between the two forms of quantum interference. To explore this possibility, two regioisomers (BIT-Zwitterion and BIT-Neutral) were synthesized and their single-molecule conductances in aprotic and protic solvents were investigated using a scanning-tunneling-microscope-based break junction technique, combined with density functional theory and quantum transport theory. We find that the protic solvent twists the geometry of BIT-Zwitterion by introducing intermolecular hydrogen bonds between the solvent and target molecule. Moreover, it increases the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecule by imposing different electrostatic gating on the delocalized HOMO and localized LUMO, leading to a lower conductance compared to that in aprotic solvent. In contrast, the conductance of BIT-Neutral increases due to a transformation from DQI to CQI originating from a change from a planar to a folded conformation in the protic solvent. In addition, the stacking between the two folded moieties produces an extra through-space transport path, which further contributes to conductance. This study demonstrates that combinations of protic solvents and regioisomers present a versatile route to controlling quantum interference and therefore single-molecule conductance, by enabling control of hydrogen bond formation, electrostatic gating and through-space transport.

A novel all-nitrogen molecular crystal N16 as a promising high-energy-density material.

All-nitrogen solids, if successfully synthesized, are ideal high-energy-density materials because they store a great amount of energy and produce only harmless N2 gas upon decomposition. Currently, the only method to obtain all-nitrogen solids is to apply high pressure to N2 crystals. However, products such as cg-N tend to decompose upon releasing the pressure. Compared to covalent solids, molecular crystals are more likely to remain stable during decompression because they can relax the strain by increasing the intermolecular distances. The challenge of such a route is to find a molecular crystal that can attain a favorable phase under elevated pressure. In this work, we show, by designing a novel N16 molecule (tripentazolylamine) and examining its crystal structures under a series of pressures, that the aromatic units and high molecular symmetry are the key factors to achieving an all-nitrogen molecular crystal. Density functional calculations and structural studies reveal that this new all-nitrogen molecular crystal exhibits a particularly slow enthalpy increase with pressure due to the highly efficient crystal packing of its highly symmetric molecules. Vibration mode calculations and molecular dynamics (MD) simulations show that N16 crystals are metastable at ambient pressure and could remain inactive up to 400 K. The initial reaction steps of the decomposition are calculated by following the pathway of the concerted excision of N2 from the N5 group as revealed by the MD simulations.

Controlling the Isomerization of Photoresponsive Molecules through a Limiting Tautomerization Strategy.

Controlling the multistage photoresponsivity remains a challenge, in part, due to the spontaneous tautomerization between isomers. Herein, we present a strategy to access three independent states (linear, cyclic keto, and cyclic enolate) of crown ether (CE)-substituted donor-acceptor Stenhouse adducts (DASAs) by limiting the tautomerization of the closed isomers. The linear-cyclic keto isomerization is reversibly triggered by treatment with metal ions (Na+ or K+) and CE, while the linear-cyclic enolate isomerization is induced by green light and heat. Density functional theory and molecular dynamics calculation results suggest that the steric effect and supramolecular interaction between the electron-donating and electron-withdrawing moieties play an important role in hindering the tautomerization between cyclic keto and cyclic enolate DASA-CE. The strategy to influence key steps in the photoswitching process inspires well-controlled multistage isomerization of photoresponsive molecules.

Insight into the Enhanced Charge Transport in Quasi-2D Perovskite via Fluorination of Ammonium Cations for Photovoltaic Applications.

Fluorinated spacer cations in quasi-2D (Q-2D) perovskites have recently been demonstrated to improve the Q-2D perovskite solar cell (PSC) performance. However, the underlying mechanism of fluorination of organic cations on the improvement is still unclear. Here, using fluorinated benzylammonium (named F-BZA) as a spacer cation in Q-2D Ruddlesden-Popper (RP) perovskites, we deeply investigate the effect of fluorination of organic cations on perovskite crystallization and intermolecular interactions for improving the charge transport and device performance. It is found that fluorination of spacer cations can slow down the crystallization rate of perovskites, resulting in vertically aligned large grains. Moreover, the interaction between the adjacent spacer cations is further enhanced, constructing a new faster charge-transport channel with a lifetime of 77 ps. Accordingly, the carrier mobility is improved by an order of magnitude and a power conversion efficiency (PCE) of 16.82% is achieved in much more stable F-BZA-based Q-2D RP PSCs, 35% higher than that of BZA-based devices (12.39%). Our results elucidate the mechanism and its importance of fluorinating spacer cations for high-performance Q-2D PSC development.

Normal & reversed spin mobility in a diradical by electron-vibration coupling.

π-conjugated radicals have great promise for use in organic spintronics, however, the mechanisms of spin relaxation and mobility related to radical structural flexibility remain unexplored. Here, we describe a dumbbell shape azobenzene diradical and correlate its solid-state flexibility with spin relaxation and mobility. We employ a combination of X-ray diffraction and Raman spectroscopy to determine the molecular changes with temperature. Heating leads to: i) a modulation of the spin distribution; and ii) a "normal" quinoidal → aromatic transformation at low temperatures driven by the intramolecular rotational vibrations of the azobenzene core and a "reversed" aromatic → quinoidal change at high temperatures activated by an azobenzene bicycle pedal motion amplified by anisotropic intermolecular interactions. Thermal excitation of these vibrational states modulates the diradical electronic and spin structures featuring vibronic coupling mechanisms that might be relevant for future design of high spin organic molecules with tunable magnetic properties for solid state spintronics.

Self-adhesive hydrogels for tissue engineering.

Hydrogels consisting of a three-dimensional hydrophilic network of biocompatible polymers have been widely used in tissue engineering. Owing to their tunable mechanical properties, hydrogels have been applied in both hard and soft tissues. However, most hydrogels lack self-adhesive properties that enable integration with surrounding tissues, which may result in suture or low repair efficacy. Self-adhesive hydrogels (SAHs), an emerging class of hydrogels based on a combination of three-dimensional hydrophilic networks and self-adhesive properties, continue to garner increased attention in recent years. SAHs exhibit reliable and suitable adherence to tissues, and easily integrate into tissues to promote repair efficiency. SAHs are designed either by mimicking the adhesion mechanism of natural organisms, such as mussels and sandcastle worms, or by using supramolecular strategies. This review summarizes the design and processing strategies of SAHs, clarifies underlying adhesive mechanisms, and discusses their applications in tissue engineering, as well as future challenges.

A nitrogen-doped asymmetric phenalenyl with a zwitterionic ground state.

Herein, an asymmetric N-doped phenalenyl (BTAP) compound has been synthesized and carefully studied for the first time. The synthesis of BTAP reveals a planar configuration and an unexpected zwitterionic ground state with the negative charge delocalized around the circumjacent part and the positive charge mainly localized on the center.

Designing of Rewritable Paper by Hydrochromic Donor-Acceptor Stenhouse Adducts.

Rewritable paper is meaningful to the recyclable and sustainable utilization of environmental resources and thus has been extensively investigated for several decades. In this work, we demonstrated an efficient and convenient strategy to fabricate rewritable paper based on reversible hydrochromism of donor-acceptor Stenhouse adducts (DASAs). The kinetics and efficiency of isomerization could be well-controlled by adjusting the surrounding temperature and humidity. Monocolored rewritable paper was prepared by coating cyclic DASA·xH2O on the paper surface. Writing, printing, stamping and patterning were realized on the rewritable paper. The information could be controllably erased by treatment in a humid atmosphere. More importantly, the rewritable paper was upgraded to multicolored by combination of two DASA materials. The color of chirography was switched by controlling the writing speed.

Carbon Spacer Strategy: Control the Photoswitching Behavior of Donor-Acceptor Stenhouse Adducts.

Understanding the relationship between chemical structure and photoswitching property of donor-acceptor Stenhouse adducts (DASAs) is necessary for developments and applications of the novel photoresponsive molecule. In the current work, we demonstrated a close relationship between the length of carbon spacer and photoswitching property of DASAs. A series of DASAs with barbituric acid substituted electron-withdrawing part and N-methylaniline substituted electron-donating part were synthesized. With shortening the carbon spacer between the phenyl and amine groups in the electron-donating part, the efficiency and rate of the light-induced linear-to-cyclic isomerization are improved in all the test solvents. The molecular energy variation during the isomerization process was investigated by density functional theory calculation to further understand the mechanism. This work provides a reliable carbon spacer strategy to control the photoswitching behavior of DASAs using chemical methods.