Strong Stacking Research Articles

Boosting Covalent Organic Framework Luminescence by Suppressing Nonradiative Pathways†

Comprehensive SummaryThe construction of luminescent two‐dimensional (2D) imine‐linked covalent organic frameworks (COFs) is a formidable challenge due to the strong interlayer stacking and bond rotations that typically suppress intramolecular charge transfer (ICT), leading to nonradiative energy dissipation. Herein, three COFs with tailored interlayer distances and bond rotations are designed to modulate the ICT behaviours. The targeted COF (TPAZ‐TPE‐COF) achieved a significantly enhanced photoluminescence quantum yield (PLQY) of 21.22% in the solid state by restricting bond rotation and enlarging the layer distance. This represents a 3.5‐fold and 530.5‐fold improvement over TPAZ‐PYTA‐COF (6.15%), which has a shortened interlayer space, and TPAZ‐PATA‐COF (0.04%), which exhibits strong bond rotations, respectively. Importantly, TPAZ‐TPE‐COF also exhibits exceptional sensing performance for iron ions, with a detection limit at the ppb level. Both experimental and theoretical analyses reveal that the prominent luminescent performance of TPAZ‐TPE‐COF is assigned to the effective suppression of nonradiative pathways, especially those arising from interlayer stacking and bond vibrations. These findings pave the way for deliberate construction of imine‐linked 2D COFs with high PL intensity, thereby expanding the portfolio of luminescent COFs with potential applications in sensing and optoelectronics.

Nitrogen‐Rich Conjugated Macrocycles: Synthesis, Conductivity, and Application in Electrochemical CO2 Capture

AbstractHere we report a series of nitrogen‐rich conjugated macrocycles that mimic the structure and function of semiconducting 2D metal–organic and covalent organic frameworks while providing greater solution processability and surface tunability. Using a new tetraaminotriphenylene building block that is compatible with both coordination chemistry and dynamic covalent chemistry reactions, we have synthesized two distinct macrocyclic cores containing Ni−N and phenazine‐based linkages, respectively. The fully conjugated macrocycle cores support strong interlayer stacking and accessible nanochannels. For the metal–organic macrocycles, good out‐of‐plane charge transport is preserved, with pressed pellet conductivities of 10−3 S/cm for the nickel variants. Finally, using electrochemically mediated CO2 capture as an example, we illustrate how colloidal phenazine‐based organic macrocycles improve electrical contact and active site electrochemical accessibility relative to bulk covalent organic framework powders. Together, these results highlight how simple macrocycles can enable new synthetic directions as well as new applications by combining the properties of crystalline porous frameworks, the processability of nanomaterials, and the precision of molecular synthesis.

Nitrogen-Rich Conjugated Macrocycles: Synthesis, Conductivity, and Application in Electrochemical CO2 Capture.

Here we report a series of nitrogen-rich conjugated macrocycles that mimic the structure and function of semiconducting 2D metal-organic and covalent organic frameworks while providing greater solution processability and surface tunability. Using a new tetraaminotriphenylene building block that is compatible with both coordination chemistry and dynamic covalent chemistry reactions, we have synthesized two distinct macrocyclic cores containing Ni-N and phenazine-based linkages, respectively. The fully conjugated macrocycle cores support strong interlayer stacking and accessible nanochannels. For the metal-organic macrocycles, good out-of-plane charge transport is preserved, with pressed pellet conductivities of 10-3 S/cm for the nickel variants. Finally, using electrochemically mediated CO2 capture as an example, we illustrate how colloidal phenazine-based organic macrocycles improve electrical contact and active site electrochemical accessibility relative to bulk covalent organic framework powders. Together, these results highlight how simple macrocycles can enable new synthetic directions as well as new applications by combining the properties of crystalline porous frameworks, the processability of nanomaterials, and the precision of molecular synthesis.

Antimicrobial Peptide with a Bent Helix Motif Identified in Parasitic Flatworm Mesocestoides corti.

The urgent need for antibiotic alternatives has driven the search for antimicrobial peptides (AMPs) from many different sources, yet parasite-derived AMPs remain underexplored. In this study, three novel potential AMP precursors (mesco-1, -2 and -3) were identified in the parasitic flatworm Mesocestoides corti, via a genome-wide mining approach, and the most promising one, mesco-2, was synthesized and comprehensively characterized. It showed potent broad-spectrum antibacterial activity at submicromolar range against E. coli and K. pneumoniae and low micromolar activity against A. baumannii, P. aeruginosa and S. aureus. Mechanistic studies indicated a membrane-related mechanism of action, and circular dichroism spectroscopy confirmed that mesco-2 is unstructured in water but forms stable helical structures on contact with anionic model membranes, indicating strong interactions and helix stacking. It is, however, unaffected by neutral membranes, suggesting selective antimicrobial activity. Structure prediction combined with molecular dynamics simulations suggested that mesco-2 adopts an unusual bent helix conformation with the N-terminal sequence, when bound to anionic membranes, driven by a central GRGIGRG motif. This study highlights mesco-2 as a promising antibacterial agent and emphasizes the importance of structural motifs in modulating AMP function.

Determinants of Unfolding Cooperativity and Binding Are Decoupled in a DNA Binding Domain.

The relative magnitudes of noncovalent stabilization energies or the coupling free energies in folded proteins are anisotropically distributed, uniquely influencing folding and functional behaviors. In this regard, the fructose repressor (FruR) DBD belonging to the LacR repressor family harbors a three-residue insertion─KQY─between the canonical second and third helices. This sequence insertion promotes a strong Tyr-Tyr stacking interaction that is not observed in related homologues. Combining experiments with simulations, we show that the Tyr-Tyr stacking contributes to a decoupled unfolding due to the localization of a large part of the stabilization energy in this specific structural region. This leads to melting temperatures from different probes spanning nearly 10 K, while concomitantly stabilizing a partially structured intermediate state. Disruption of the aromatic stacking interaction via an alanine mutation promotes a molten-globular state whose native ensemble is replete with non-native interactions while displaying enhanced thermodynamic fluctuations and minimal calorimetric cooperativity. Surprisingly, the molten-globular variant of FruR DBD binds to the operator site on DNA with an affinity similar to that of the wild-type but with altered secondary-structure characteristics in the bound state, underscoring the chaperone-like role of DNA through its large negative electrostatic potential. FruR DBD thus appears to be at the verge of disorder as expected of an entropically destabilizing three-residue insertion but is rescued by the aromatic stacking interaction that distinctly dictates the finer details of stability, cooperativity, and binding.

Efficient and Stable All-Polymer Solar Cells Enabled by Dual Working Mechanism.

Ternary strategy with integration characteristics and adaptability is a simple and effective method for blooming of the performance of photovoltaic devices. Herein, a novel wideband gap polymer donor PBB2-Hs is synthesized as the guest component to optimize all-polymer solar cells (all-PSCs). High-energy photon absorption and long exciton lifetime of PBB2-Hs constitute efficient energy transfer. Good miscibility and cascade energy levels promote the formation of alloy-like structure between PBB2-Hs and host system. The dual working mechanisms greatly improve photon capture and charge transfer in active layers. Additionally, the introduction of PBB2-Hs also optimizes the ordered molecular stacking of acceptors and suppresses molecular peristalsis. Upon adding 15 wt% PBB2-Hs, the ternary all-PSC achieved a champion efficiency of 17.66%, and can still maintain 82% photostability (24h) and 91% storage stability (1000h) of the original PCE. Moreover, the strong molecular stacking and entanglement between PBB2-Hs and the host material increased the elongation at break of ternary blend film by 1.6 times (16.2%), allowing the flexible device to maintain 83% of the original efficiency after 800 bends (R = 5mm). This work highlights the effectiveness of guest polymer on simultaneously improving photovoltaic performance, photostability and mechanical stability in all-PSCs.

Large-Scale Syntheses of Multicolor Stimulus Responsive Room-Temperature Phosphorescent Polymer-Carbonyl-Modified Carbon Nitrogen Quantum Dots.

Carbonyl-modified solid-state carbon nitrogen quantum dots (m-O═CNQDs) have emerged as promising room-temperature phosphorescent (RTP) materials close to commercialization. However, high-crystallinity m-O═CNQDs are insensitive to external stimuli such as water and heat due to strong stacking interactions between layers, restricting their applications in stimulus responsive fields. Here, a polymer template space-confined growth strategy is established for the large-scale synthesis of water stimulus responsive polyvinylpyrrolidone-functionalized m-O═CNQDs with ultralong room-temperature phosphorescence (181 ms) using urea and PVP as precursors. Theoretical and experimental results indicate that the PVP template linked at the rim of m-O═CNQDs formed by in situ self-polymerization of urea inhibits interactions between layers and increases their affinity for water, which is the key to increasing their sensitivity with water. This strategy offers a new path for developing commercial stimulus responsive RTP materials.

Enhancing charge transport in isoindigo-based donor–acceptor copolymers by combining ionic doping with polar alkoxy side chains

Side chains of polymers play a crucial role in manipulating polymer interchain interactions, especially polar side chains that promote strong molecular stacking and facilitate ionic diffusion.

Investigation of the microscopic properties of natural structured clay

Conducting quantitative research on the microstructure of soft clay can reveal the essence of its soil mechanical behavior, which is of important practical significance for geological disaster risk assessment and prevention. To quantitatively investigate the microscopic properties of natural structured clay, soft clay soils from various sedimentary environments in the Hangzhou Estuarine Bay area were chosen as the research subject in this study. Subsequently, a comprehensive investigation into the microstructure of clay was conducted, involving X-ray phase analysis and SEM imaging analysis. The results revealed the following: (1) In comparison to the deep clay deposited in fluvial-lacustrine environments, the shallow mucky clay in marine sediments had a higher clay mineral content, accounting for 48%. Illite makes up the majority of it, with minor levels of kaolinite and montmorillonite being present. (2) The shallow mucky clay in the Hangzhou Estuarine Bay area had a typical agglomerate-flocculated structure. In contrast, the deeper clay showed a flocculated structure with less uniform particle sizes, strong stacking randomness, poor directional alignment of soil pores, and tends to form arrangements where edges are adjacent to faces or edges are adjacent to other edges. (3) Compared to the deep clay deposited in fluvial-lacustrine environments, the marine-deposited shallow mucky clay displayed orderly pore arrangements, strong directional alignment, significant pore shape variability, and minimal pore size changes between adjacent pores. The microstructure of soil plays a crucial role in determining the physical, mechanical, and other engineering properties of the soil. This study provides insightful information about the relationship between clay microstructure and geotechnical characteristics in Hangzhou and the surrounding areas.

Recent advances in aggregation-induced emission-active type I photosensitizers with near-infrared fluorescence: From materials design to therapeutic platform fabrication.

Near-infrared (NIR) fluorescence imaging-guided photodynamic therapy (PDT) technology plays an important role in treating various diseases and still attracts increasing research interests for developing novel photosensitizers (PSs) with outstanding performances. Conventional PSs such as porphyrin and rhodamine derivatives have easy self-aggregation properties in the physiological environment due to their inherent hydrophobic nature caused by their rigid molecular structure that induces strong intermolecular stacking π-π interaction, leading to serious fluorescence quenching and cytotoxic reactive oxygen species (ROS) reduction. Meanwhile, hypoxia is an inherent barrier in the microenvironment of solid tumors, seriously restricting the therapeutic outcome of conventional PDT. Aforementioned disadvantages should be overcome urgently to enhance the therapeutic effect of PSs. Novel NIR fluorescence-guided type I PSs with aggregation-induced emission (AIE), which features the advantages of improving fluorescent intensity and ROS generation efficiency at aggregation as well as outstanding oxygen tolerance, bring hope for resolving aforementioned problems simultaneously. At present, plenty of research works fully demonstrates the advancement of AIE-active PDT based on type I PSs. In this review, cutting-edge advances focusing on AIE-active NIR type I PSs that include the aspects of the photochemical mechanism of type I ROS generation, various molecular structures of reported type I PSs with NIR fluorescence and their design strategies, and typical anticancer applications are summarized. Finally, a brief conclusion is obtained, and the underlying challenges and prospects of AIE-active type I PSs are proposed.

Lateral and vertical characteristics of floodplain aggradation cycles in the lower Eocene Willwood Formation, Bighorn Basin, Wyoming, USA

Sedimentation on river floodplains is a complex process that involves overbank flooding, crevasse splaying, and river avulsion. The resulting floodplain stratigraphy often exhibits floodplain aggradation cycles with alternating fine-grained overbank flooding deposits that underwent significant petrogenesis, and coarser-grained, avulsion-belt deposits largely devoid of pedogenic impact. These cycles are linked to lateral migration and avulsion of channels driven by internal dynamics, external factors, or a combination of both. To better understand the spatial and vertical variability of such floodplain aggradation cycles, we map these in three dimensions using a photogrammetric model of the lower Eocene Willwood Formation in the northern Bighorn Basin, Wyoming, USA. This allows identifying 44 floodplain aggradation cycles in ∼300 m of strata with an average thickness of 6.8 m and a standard deviation of 2.0 m. All the cycles are traceable over the entire model, pointing to their spatial consistency over the 10 km2 study area. At the same time, rapid lateral thickness changes of the floodplain aggradation cycles occur with changes up to 4 m over a lateral distance of 400 m. Variogram analyses of both field and numerical-model results reveal stronger consistency of floodplain aggradation cycle thicknesses along the paleoflow direction compared to perpendicular to paleoflow. Strong compensational stacking occurs at the vertical scale of 2−3 floodplain aggradation cycles (14−20 m), while full compensational stacking occurs at larger scales of more than six floodplain aggradation cycles (>41 m). The lateral and vertical thickness variability of the floodplain aggradation cycles, as well as their compensational stacking behavior, are interpreted to be dominantly driven by autogenic processes such as crevasse splaying and avulsing that preferentially fill topographic lows. External climate forcing may have interacted with these autogenic processes, producing the laterally persistent and vertically repetitive floodplain aggradation cycles. The spatial variability of floodplain aggradation cycles demonstrated in this study highlights again the need for three-dimensional data collection in alluvial floodplain settings rather than depending on one-dimensional records.

DNA/BSA binding studies and in vitro anticancer and antibacterial studies of isoelectronic Cu(I)- and Ag(I)-pyridinyl Schiff base complexes incorporating triphenylphosphine as co-ligands

Four mononuclear Ag(I) and Cu(I) Schiff base complexes of the type [M(L)(PPh3)2]X [where M = Ag+ or Cu+, L = (E)-N-(2-fluorophenyl)-1-(pyridin-2-yl)methanimine (fpm) or (E)-1-(pyridin-2-yl)-N-(p-tolyl)methanimine (ptm) and X = NO3–] have been synthesized and characterized by various spectroscopic and analytical techniques. The analysis shows that the complexes are four-coordinates formed via the nitrogen atoms of a bidentate fpm or ptm ligands and two phosphorus atoms from the triphenylphosphine co-ligands. Two of the complexes were structurally characterized by single crystal X-ray diffraction revealing a distorted trigonal pyramidal geometry around the Ag(I) or Cu(I) center. The binding affinity of the complexes with calf thymus-DNA (CT-DNA) and bovine serum albumin (BSA) was determined using UV–visible spectroscopy. The interaction of the complexes with CT-DNA revealed the strong stacking interaction between the aromatic chromophore of the complexes and the base pairs of the CT-DNA. The study of the complexes with BSA showed moderate affinity to BSA, suggesting that complexes 1–4 can be delivered and dispositioned in vivo. Invitro anticancer activity of the synthesized complexes was evaluated against non-cancerous human embryonic kidney 293 (HEK293), cervical cancer cell (HELA), breast cancer cell (MDA-MB231) and malignant human melanoma cell (A375). High antiproliferative effects of the complexes on HELA (with EC50 values between 1.82±1.23 and 10.66±2.87 μM better than cisplatin with EC50 > 50 μM) and MDA-MB231(≈2 to 7-fold effective than cisplatin) were recorded. Further, the invitro antibacterial activity of the synthesized compounds was evaluated against S. aureus, E. coli, S. typhi and P. aeruginosa using the disc diffusion method from which the Cu(I) complexes showed better inhibitory effects than the Ag(I) complexes.

Binding of Mammea A/AA (MA) to calf thymus DNA revealed by the ratiometric absorbance of MA in the UV-visible range molecular dynamic simulations and TD-DFT calculations

The in vitro anti-proliferative activity of MA ( 5,7-dihydroxy-8-(3-methylbut-2-enyl)-6-(3-methyl-1-oxobutyl)-4-phenyl[1]2H-[1]benzopyran-2-one)on a variety of cancer cells was previously demonstrated. This work strives to understand the mechanisms by which MA exerts this biological activity. Thereafter, the binding of MA to calf thymus DNA was studied by monitoring the change in the UV-visible absorbance of MA. It was found that, the response of MA to binding with calf thymus DNA is characterised by an increase in the AS/AL ratio of the absorbance of the longest wavelength absorption band to the shortest one, and the appearance of a new band at about 377 nm assigned to S0→S1 transition, which is red shifted as compared to free MA. From the bands ratio, the binding constant is found to be 4.3x105 M−1, indicating strong binding. The deduced binding free energy, enthalpy and entropy are −7.7 kcal/mol, −10.89 ± 0.28 kcal/mol and −54.46 ± 4 J/K, respectively, indicating that MA binds to DNA by a non-bonding Van der Waals type interactions and hydrogen bonds. Further study with classical molecular dynamics shows that MA binds to DNA by intercalation, where it is positioned between two AT base pairs. Unlike isolated MA, TDDFT calculations on ten images extracted from the MD trajectory show that, the frontier molecular orbitals of the complex are distributed over the DNA and MA. This indicates a strong stacking interaction and then explains the hypochromism and the red shift of the S0→S1 transition. The present work demonstrates the potency of MA as antitumor compound and as absorbance-based molecular probe. Communicated by Ramaswamy H. Sarma

Electrochemical aptamer biosensor for DNA detection based on label-free aptamers

Electrochemical aptasensor has been broadly advanced for nucleic acid detection. However, it is a long-term goal to design an aptasensor with high specificity, flexibility, and simplicity. In this work, we develop a strategy of triblock DNA probe, which consists of two DNA probes at both ends and ployA fragments in the middle as probe-polyA-probe. PolyA fragment has high affinity to the surface of gold electrode, so it can be assembled on the electrode surface via polyA instead of traditional Au-S bonds. When the target DNA is simultaneously hybridized with the two capture probes, the hybridization stability can be improved due to the strong base stacking effect. [Ru(NH3)6]3+, as signal probe, can be electrostatically adsorbed on the negatively charged DNA skeleton. A wide linear range (10 pM-10 μM) is obtained with a detection limit of 2.9 pM. Our electrochemical aptasensor has good repeatability, stability, and specificity. More importantly, the electrochemical sensor can successfully detect DNA in human serum samples, which proves its practical value and extensive applicability in complex environment.

Rational optimization of g-C3N4/Co3O4 nanocomposite for enhanced photodegradation of Rhodamine B dye under visible light

Heterogeneous catalysis is widely known as an efficient, clean, and low-cost technology to mitigate the environmental pollution of industrial effluents. This research aimed at optimizing the preparation and characterization of efficient g-C3N4/Co3O4 nanocomposite for catalytic removal of Rhodamine B (Rh B) dye. The detected XRD peaks for the prepared nano-Co3O4 are matched with the cubic crystal structure. In contrast, the broad peak at 27.3° corresponding to the graphite reflection of hkl (002) was noticeably weakened in the XRD pattern of the g-C3N4/Co3O4 composite. FTIR spectra of g-C3N4/Co3O4 nanocomposites revealed the active vibrational modes of each Co3O4 and g-C3N4 component. The microstructure study of g-C3N4 showed the strong interlayer stacking of carbon nitride nanosheets, while the surface morphology of g-C3N4/Co3O4 nanocomposite revealed a hybrid particulate system. EDS analysis indicated that the spot area of g-C3N4/Co3O4 confirmed the chemical ratios of carbon, nitrogen, cobalt, and oxygen. BET measurements of g-C3N4/Co3O4 showed a significant increase in the surface area and pore volume of single components due to the lamination of stacked g-C3N4 nanosheets by the intercalated Co3O4 nanoparticles. The prepared 30% g-C3N4/Co3O4 revealed the lowest value of Eg ~1.2 eV and the highest light absorptivity suggesting strong promotion for the photocatalytic performance under visible light. The maximum photocatalytic activity of about 87% was achieved by 30% g-C3N4/Co3O4 due to the photonic enhancement, which reduces the recombination of excited electrons. The developed nanocomposite with a g-C3N4/Co3O4 ratio of 0.3 exhibited high stability in its photocatalytic performance after four recycling times, and a slight decrease of about 7% was estimated after the 5th reuse test.

Donor–Acceptor Covalent–Organic Frameworks Based on Phthalimide as an Electron-Deficient Unit for Efficient Visible-Light Catalytic Hydrogen Evolution

Donor-acceptor two-dimensional covalent-organic frameworks (COFs) have great potential as photocatalysts for hydrogen evolution because of their tunable structures, ordered and strong stacking, high crystallinity, and porosity. Herein, an acceptor unit, namely phthalimide, has been employed for the first time to construct COFs. Two donor-acceptor COFs (TAPFy-PhI and TAPB-PhI) have been successfully synthesized via a Schiff base reaction using phthalimide as the acceptor and 1,3,6,8-tetrakis(4-aminophenyl)pyrene (TAPFy) and 1,3,5-tris(4-aminophenyl)benzene (TAPB) as donors. The synthesized COFs exhibited high crystallinity, permanent porosity, excellent chemical stability, suitable band gaps, and broad visible-light absorption. In the presence of ascorbic acid (sacrificial reagent), the TAPFy-PhI COF exhibited an efficient photocatalytic performance with a hydrogen evolution rate of 1763 μmol g-1 h-1. Moreover, the photocatalytic performance was further improved by the addition of Pt (1 wt %) as a cocatalyst, and the hydrogen evolution rate reached 2718 μmol g-1 h-1.

C-B-A Test of DNA Force Fields.

The DNA duplex may be locally strongly bent in complexes with proteins, for example, with polymerases or in a nucleosome. At such bends, the DNA helix is locally in the noncanonical forms A (with a narrow major groove and a large amount of north sugars) or C (with a narrow minor groove and a large share of BII phosphates). To model the formation of such complexes by molecular dynamics methods, the force field is required to reproduce these conformational transitions for a naked DNA. We analyzed the available experimental data on the B-C and B-A transitions under the conditions easily implemented in modeling: in an aqueous NaCl solution. We selected six DNA duplexes which conformations at different salt concentrations are known reliably enough. At low salt concentrations, poly(GC) and poly(A) are in the B-form, classical and slightly shifted to the A-form, respectively. The duplexes ATAT and GGTATACC have a strong and salt concentration dependent bias toward the A-form. The polymers poly(AC) and poly(G) take the C- and A-forms, respectively, at high salt concentrations. The reproduction of the behavior of these oligomers can serve as a test for the balance of interactions between the base stacking and the conformational flexibility of the sugar-phosphate backbone in a DNA force field. We tested the AMBER bsc1 and CHARMM36 force fields and their hybrids, and we failed to reproduce the experiment. In all the force fields, the salt concentration dependence is very weak. The known B-philicity of the AMBER force field proved to result from the B-philicity of its excessively strong base stacking. In the CHARMM force field, the B-form is a result of a fragile balance between the A-philic base stacking (especially for G:C pairs) and the C-philic backbone. Finally, we analyzed some recent simulations of the LacI-, SOX-4-, and Sac7d-DNA complex formation in the framework of the AMBER force field.

An imidazole based luminescent Zn (II) metal–organic framework for sensing of nitroaromatic explosives

The Zn(II)-based IFP-1 (IFP = imidazolate framework Potsdam) was successfully synthesized by solvothermal process to detect the nitroaromatic compounds (NACs) including nitrobenzene (NB), 1,3‑dinitrobenzene (1,3-DNB), 1,2‑dinitrobenzene (1,2-DNB), 1,4‑dinitrobenzene (1,4-DNB), 4‑nitrotoluene (4-NT) and 2,4,6-trinitrophenol (TNP). It was found that IFP-1 gives the maximum emission intensity at 338 nm upon excitation at 288 nm. The quenching constant (KSV) for all the analytes was found in the order as follows: TNP > DNP > NB > NT > 1,2-DNB > 1,4-DNB > 1,3-DNB. The localization of the amide group of 2-methylimidazolate-4-amide-5-imidate ligand in the walls of the channels provides feasible interacting sites for incoming analytes. These suitable geometrical characteristics of IFP-1 provide close proximity to NACs leading to their prompt sensing ability. The fluorescence intensity was reduced by 71 % in the presence of TNP. IFP-1 shows high selective detection of TNP even in presence of other nitroaromatic compounds. However, the sensing ability of IFP-1 towards TNP is highest over other NACs with high quenching constant (Ksv) of 1.12 × 105 M−1 and a low detection limit of 0.23 µM, indicating a good detection limit. A detailed investigation has been carried out on the fluorescence quenching mechanism by DFT calculation. This study showed that the high sensitivity of the compound towards TNP is possible because of the formation of non-fluorescent ground state complex formation driven by strong pi-pi stacking interaction and electrostatic hydrogen bond interactions.

Recent Research Progress of Organic Small-Molecule Semiconductors with High Electron Mobilities.

Organic electronics has made great progress in the past decades, which is inseparable from the innovative development of organic electronic devices and the diversity of organic semiconductor materials. It is worth mentioning that both of these great advances are inextricably linked to the development of organic high-performance semiconductor materials, especially the representative n-type organic small-molecule semiconductor materials with high electron mobilities. The n-type organic small molecules have the advantages of simple synthesis process, strong intermolecular stacking, tunable molecular structure, and easy to functionalize structures. Furthermore, the n-type semiconductor is a remarkable and important component for constructing complementary logic circuits and p-n heterojunction structures. Therefore, n-type organic semiconductors play an extremely important role in the field of organic electronic materials and are the basis for the industrialization of organic electronic functional devices. This review focuses on the modification strategies of organic small molecules with high electron mobility at molecular level, and discusses in detail the applications of n-type small-molecule semiconductor materials with high mobility in organic field-effect transistors, organic light-emitting transistors, organic photodetectors, and gas sensors.

Mechanical codes of chemical-scale specificity in DNA motifs.

In gene transcription, certain sequences of double-stranded (ds)DNA play a vital role in nucleosome positioning and expression initiation. That dsDNA is deformed to various extents in these processes leads us to ask: Could the genomic DNA also have sequence specificity in its chemical-scale mechanical properties? We approach this question using statistical machine learning to determine the rigidity between DNA chemical moieties. What emerges for the polyA, polyG, TpA, and CpG sequences studied here is a unique trigram that contains the quantitative mechanical strengths between bases and along the backbone. In a way, such a sequence-dependent trigram could be viewed as a DNA mechanical code. Interestingly, we discover a compensatory competition between the axial base-stacking interaction and the transverse base-pairing interaction, and such a reciprocal relationship constitutes the most discriminating feature of the mechanical code. Our results also provide chemical-scale understanding for experimental observables. For example, the long polyA persistence length is shown to have strong base stacking while its complement (polyAc) exhibits high backbone rigidity. The mechanical code concept enables a direct reading of the physical interactions encoded in the sequence which, with further development, is expected to shed new light on DNA allostery and DNA-binding drugs.