The Solid-State Multi-Color Fluorescence Switching from a [2.2]Paracyclophane-Based Triarylborane.

The fluorophores, the fluorescence of which can be switched between multi bright colors in the solid state, show promising applications not only in the sophisticated multicolor display but also in the advanced encryption and anti-counterfeiting systems. However, it is very challenging to obtain such fluorophores. Herein, we disclose such an example, g-BPhANMe2-Cp, which contains an electron-donating dimethylamino (NMe2) and an electron-accepting [(2-dimesitylboryl)phenyl]acetyl at the pseudo-gem position of [2.2]paracyclophane skeleton. This molecule can display tricolor mechanochromic luminescence (MCL) due to the different responses of the mechanically ground amorphous state to heating and solvent-fuming. Owing to the absence of intermolecular π-π interactions in the solid state, the fluorescence efficiency is very high irrespective of its morphological state (ΦF=0.60-0.87). Moreover, this molecule also displays reversible acidochromic luminescence (ACL) by protonation and deprotonation of NMe2 with trifluoroacetic acid (TFA) and triethylamine (TEA), respectively. The protonated sample fluoresces (ΦF=0.31) at much shorter wavelength due to the interruption of intramolecular charge transfer process. Therefore, with the combination of tricolor MCL and ACL properties, the solid-state emission of g-BPhANMe2-Cp can be switched among four bright fluorescence colors of yellow, green, cyan and blue via treatment with appropriate stimulus.

Two-Photon-Excited Fluorescent Tetrabranched Triphenylborane Featuring the Cooperative Effect of Branching in Two-Photon Absorption.

We here disclose a new type of two-photon-excited fluorescent triarylborane, tetrabranched triphenylborane 1, which contains four electron-donating [4-(N,N-diphenylamino)phenyl]ethynyl branches at 2,6-positions of two phenyl rings. The cross section of 1 reaches 275 GM (1 GM = 10-50 cm4 s photon-1) in tetrahydrofuran. Compared with dibranched triphenylborane 2, the 2-fold increase in the number of electron-donating branches induces a 3.6-fold increase in the two-photon absorption cross section, suggesting the great cooperative effect of branching in the enhancement of two-photon absorption.

Two-Photon Excited Fluorescent 3,3'-Diamino-5,5'-Diboryl-2,2'-Bithienyls Featuring a Quadrupolar Structure.

The quest for fluorophores exhibiting large two-photon absorption cross sections and high fluorescence efficiency is an important topic. Two 2,2'-bithienyl derivatives are disclosed which contain two N,N-disubstituted amino and two dimesitylboryl groups at 3,3'- and 5,5'-positions, respectively. Despite the great steric effect of amino groups, the bithienyl skeleton still adopts a coplanar geometry. Herein, they are characterized by a quadrupolar structure and display good fluorescence efficiency and large two-photon absorption cross sections up to 473 GM.

Chiral Triarylborane-Based Small Organic Molecules for Circularly Polarized Luminescence.

Circularly polarized luminescence (CPL) has shown promising application potentials in 3D display, optical data storage, smart sensors/probers, CPL lasers, and light source for asymmetric photosynthesis. In the last decade, the CPL-active small organic molecules (CPL-SOMs) have attracted rapidly increasing research interest owing to the great advantages of SOMs, such as high luminescence efficiency, facile modification of chemical structure, fine emission wavelength tuning, precise relationships between structure and properties, and as well as easy fabrication. Promoted by the unique effects of boryl group, such as strong electron-accepting ability, great steric effect, and Lewis acidity to bind with Lewis bases, we herein summarized our recent research results about the creation of CPL-SOMs by modification of chiral scaffolds, such as [2.2]paracyclophane, [5]/[7]helicene, and binaphthyl, with boryl group. The preliminary results have well demonstrated that the chiral triarylborane-based SOMs exhibit promising CPL properties, such as intense CPL in combination of high luminescence dissymmetry factor (|glum |) with high fluorescence efficiency, solvent-induced sign inversion, facile emission wavelength tuning, high fluorescence efficiency in the solid, and substituent-induced sign inversion.

The mechanism of semiconductor to metal transition in the hydrogenation of VO2: a density functional theory study.

VO2 is a glamorous material with specific metal-semiconductor-transition (MST). The hydrogenation of VO2 could make it a promising material for application in an ambient environment. In this work, we reveal the hydrogenation of VO2 by modulating the hydrogen content and monitoring interaction models, adsorption energies, the density of states, electron density, and charge transfer between hydrogen and the VO2 surface. The monoclinic VO2(020) surface shows a distinct electronic polarization, and the majority spin band gap is larger than the minority spin band gap. The energy gap of the monoclinic VO2 surface is highly dependent on the majority spin band. The interaction between hydrogen and oxygen in the first layer of the VO2 surface is stronger than those in other layers. The energy gap on the surface of VO2 decreases gradually with increasing hydrogen content, and when twelve hydrogen atoms are adsorbed on the surface, an energy gap of 0 eV eventually appears, suggesting that monoclinic VO2 turns into a metallic conductor from a semiconductor. In the process of VO2 hydrogenation, the electron transfer only occurs between hydrogen and its connected oxygen atoms on the VO2 surface, and vanadium atoms just play an intermediary role.

Circularly Polarized Luminescence Switching in Small Organic Molecules.

The circularly polarized luminescence (CPL) switching is of significant interest for applications in security technologies and sensing devices. Small organic molecules (SOMs) show several advantages over metal complexes, supramolecular assemblies, and polymers. Therefore, the recent progress on the CPL switching in SOMs is here reviewed. The results are summarized based on the strategies used to tune factors that influence the emission properties, and thus, to realize CPL switching. The strategies that have been adopted include promoting the excimer formation of fluorescent units, changing the conformation of fluorophores, tuning the electronic structure of the π-skeleton/substituent, and modulating the intramolecular charge-transfer dynamics.

1,1'-Binaphthyl Consisting of Two Donor-π-Acceptor Subunits: A General Skeleton for Temperature-Dependent Dual Fluorescence.

Temperature-dependent dual fluorescence with the anti-Kasha's rule is of great interest, but is a very challenging property to achieve in small organic molecules. The highly sensitive temperature-dependent dual fluorescence of 2,2'-bis(dimethylamino)-6,6'-bis(dimesitylboryl)-1,1'-binaphthyl (BNMe2 -BNaph), which essentially consists of two donor-π-acceptor (D-π-A) subunits, inspired the exploration of the importance of its structural features and the general utility of this molecular design. The reference compound MBNMe2 -BNaph, which lacks one electron-accepting Mes2 B, is found to show less sensitive temperature-dependent dual fluorescence, suggesting that the structure of BNMe2 -Bnaph, consisting of two symmetrical D-π-A subunits, is very important for achieving highly sensitive temperature-dependent dual fluorescence. In addition, it is found that another two 1,1'-binaphthyls, CHONMe2 -BNaph and CNNMe2 -BNaph, which also consist of two D-π-A subunits with Mes2 B groups replaced by CHO and CN, respectively, also show temperature-dependent dual fluorescence, with the fluorescence changing in a similar manner to BNMe2 -BNaph, indicating the general utility of the current molecular design for temperature-dependent dual fluorescence. Furthermore, the temperature-dependent dual fluorescence behaviors, such as the relative intensities of the two emission bands, the separation of the two emissions bands, and the sensitivity of the fluorescence intensity ratio to temperature, are greatly influence by the electron acceptors.

2,2'-Diamino-6,6'-diboryl-1,1'-binaphthyl: A Versatile Building Block for Temperature-Dependent Dual Fluorescence and Switchable Circularly Polarized Luminescence.

Temperature-dependent dual fluorescence and switchable circularly polarized luminescence (CPL) are two highly pursued but challenging properties for small organic molecules (SOMs). We herein disclose a triarylborane π-system based on a 2,2'-diamino-6,6'-diboryl-1,1'-binaphthyl scaffold that can serve as a versatile building block for achieving these two properties by simply choosing different amino groups. BNMe2 -BNaph with less bulky dimethylamino groups displays temperature-dependent dual fluorescence, and can thus be used as a highly sensitive ratiometric fluorescence thermometer. On the other hand, BNPh2 -BNaph with bulky diphenylamino groups exhibits intense fluorescence in both solution and in the solid state. A change of solvent from nonpolar cyclohexane to highly polar MeCN not only shifts the CPL position to much longer wavelength but also inverts the CPL sign. In addition, the complexation of BNPh2 -BNaph with fluoride greatly enhances the CPL intensity.

Interactions of Oxygen and Water Molecules with Pyrite Surface: A New Insight.

Pyrite is the most common sulfide in nature, and it is well-known for its roles in acid mine drainage, flotation separation of useful metal (Cu, Pb, Zn, and Mo) sulfide minerals, optoelectronic and photovoltaic application, pneumoconiosis, and even in the origin of life. However, the detailed oxidation behaviors of pyrite are still unclear and not well-understood. New oxidation pathways by O2 on the pyrite (100) surface have been found in this work for the first time using density functional theory simulation; that is, besides Fe sites, S sites are also possible oxidation sites in the initial oxidation state of pyrite, where easier and stronger oxidation may occur. This is the first time to confirm the other researchers' conjecture on the direct oxidation of S sites, which explains the isotopic composition experiments that a minor amount of O2 is permanently incorporated into SO42- during pyrite oxidation (O in SO42- is mainly derived from water). We constructed various H2O-O2 coadsorption models on the pyrite surface by considering the adsorption sequence of H2O and O2. It is found that the H2O molecule undergoes step-wise dissociation in the presence of the O2 molecule. Hydroxyl radical •OH is the reactive oxygen species during H2O dissociation. Cyclic voltammetric measurements confirm the presence of •OH. In addition, H2O2 may also be formed on the surface in terms of H2O-then-O2 sequence adsorption.

Fortunellin protects against high fructose-induced diabetic heart injury in mice by suppressing inflammation and oxidative stress via AMPK/Nrf-2 pathway regulation.

Inflammation and oxidative stress contribute to the progression of diabetic cardiomyopathy (DCM). The study was first designed to calculate the role of an anti-inflammatory and anti-oxidant Fortunellin (For) in high fructose-induced cardiac injury in diabetic mice. Fortunellin was found to be none of toxicity to mice and cells using various assays. High fructose was used to induce mice with diabetes. The heart histopathological changes and cardiac function were measured. Fortunellin significantly attenuated the score of histopathological alterations and alleviated heart function, accompanied with reduced inflammation and oxidative stress. The pro-inflammatory cytokines and the expression of p-IκB kinase α (IKKα), p-IκBα, and p-nuclear factor-κB (NF-κB) were dramatically reduced by Fortunellin, while superoxide dismutase (SOD), catalase (CAT), heme oxygenase-1 (HO-1) and p-AMP-activated protein kinase (AMPK) were significantly enhanced. Moreover, in H9C2 cells with nuclear factor erythroid 2-related factor 2 (Nrf2) knock-down abolished the prevention of Fortunellin against cardiac injury, proved by elevated inflammatory response and oxidative stress. Suppression of p-AMPK reduced the level of Nrf2 and HO-1 induced by Fortunellin, eliminating the protective role of Fortunellin. For the first time, our study suggested that Fortunellin protected against fructose-induced inflammation and oxidative stress by enhancing AMPK/Nrf2 pathway in diabetic mice and cardiomyocytes with fructose treatment.

RIP2 deficiency attenuates cardiac hypertrophy, inflammation and fibrosis in pressure overload induced mice.

Although the pathological cardiac hypertrophy presents a leading cause of morbidity and mortality worldwide, our knowledge of the molecular mechanisms underlying the disease is still poor. Here, we reported that receptor-interacting serine/threonine-protein kinase 2 (RIP2), promoting pro-inflammatory gene expression, enhanced the pathological cardiac hypertrophy in animals. The effects of RIP2 on the cardiac hypertrophy triggered by pathological stimuli have not been fully investigated. In our study, mice were subjected to aortic banding (AB) surgery to explore the pathological, echocardiographic and molecular mechanisms. RIP2 expressed highly in cardiomyocytes after AB operation in wild type (WT) mice. RIP2-knockout (KO) attenuated cardiac hypertrophy, inflammation and fibrosis in mice 4 weeks after AB-surgery. First, RIP2 knockout down-regulated hypertrophic markers of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and ß-myosin heavy chain (ß-MHC) in the heart of AB-operated mice.in addition, RIP2-deficiency reduced toll-like receptor 4/myeloid differentiation factor 88/nuclear factor kappa B (TLR4/MyD88/NF-κB) activation, mitogen-activated protein kinases (MAPKs) phosphorylation and transforming growth factor-ß1 (TGF-ß1)/SMADs expressions, contributing to the suppression of inflammatory response and fibrosis, as further evidenced by down-regulated pro-inflammatory cytokines, including Tumor necrosis factor-α (TNF-α), interleukin (IL)-1ß, IL-6 and IL-18, as well as fibrosis markers of Collagen I, Collagen III and α-smooth muscle actin (α-SMA). Taken together, our data indicated that RIP2-deficience ameliorated cardiac hypertrophy, inflammation and fibrosis through modulating multiple signaling pathways.

Esophageal carcinoma: Ex vivo evaluation by high-spatial-resolution T2 -mapping MRI compared with histopathological findings at 3.0T.

PURPOSE: To prospectively determine the feasibility of T2 -mapping magnetic resonance imaging (MRI) to quantitatively describe the signal characteristics of the normal esophageal wall and assess the depth of esophageal wall invasion by carcinoma at 3.0T. MATERIALS AND METHODS: Thirty-two patient specimens, each having foci of carcinoma, were studied using 3.0T MR. Freehand regions of interest were placed to measure the T2 value of the normal esophageal layers and were compared with the regions of carcinoma. Three independent readers reviewed the MR images to evaluate the depth of carcinoma invasion; when the three radiologists could not fully agree with each other, the final stage was determined by consensus. The Games-Howell test was used to compare the difference between the normal esophageal layers and carcinoma. Spearman correlation coefficient analysis was used to compare the stage at MRI with that at histopathological analysis. The interobserver agreement was compared with Cohen's kappa. The sensitivity, specificity, and accuracy for detecting carcinoma invasion were calculated. RESULTS: The T2 values between the carcinoma and normal esophageal layers were different (all P < 0.01), except for the inner circular muscle (P = 0.511). The T2 value of each layer of the normal esophageal wall was also different from that of the adjacent layer (all P < 0.01). In 29 of 32 lesions, the depth of the esophageal wall invasion determined by MR was consistent with the histopathological stage (r = 0.969, P < 0.001). The sensitivity, specificity, and accuracy were 80%, 96.3%, and 93.8%, respectively, for invasion into the mucosa; 77.8%, 95.7%, and 90.6%, respectively, for invasion into submucosa; 100%, 95.8%, and 96.9%, respectively, for invasion into muscularis propria; and 100%, 100%, and 100%, respectively, for invasion into the adventitia. CONCLUSION: T2 -mapping MR images obtained using a 3.0T MR scanner can be used to depict the precise histopathological layers of the esophageal wall clearly and provide excellent diagnostic accuracy for assessing esophageal carcinoma invasion. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;45:1609-1616.

Charge-Transfer Emitting Triarylborane π-Electron Systems.

Triarylboranes have attracted significantly increasing research interest as a remarkable class of photoelectronic π-electron materials. Because of the presence of vacant p orbital on the B center, the boryl group is a very unique electron acceptor that exhibits not only electron-accepting ability through p-π* conjugation but also high Lewis acidity to coordinate with Lewis bases and steric bulk arising from the aryl substituent on the B center to get enough kinetic stability. Thus, the incorporation of a trivalent B element into π-conjugated systems is an efficient strategy to tune the electronic and stereo structures and thus the photoelectronic properties of π-electron systems. When an electron-donating group, such as amino, is present, triarylboranes would likely display intramolecular charge-transfer transitions. These kinds of molecules are often highly emissive. In addition, the geometry of the molecules has a great impact on the emission properties. In this Forum Article, we herein describe our recent progress on the charge-transfer emitting triarylborane π-electron systems with novel geometries, which include the lateral boryl-substituted π-system with amino groups at the terminal positions, the o,o'-substituted biaryl π-system with boryl and amino groups at the o,o'-positions, a triarylborane-based BODIPY system, and a B,N/S-bridged ladder-type π-system. We mainly put the emphasis on the molecular design concept, structure-property relationships, intriguing emission properties and great applications of the corresponding triarylborane π-systems.

Chirality Relay in 2,2'-Substituted 1,1'-Binaphthyl: Access to Propeller Chirality of the Tricoordinate Boron Center.

It is a challenging issue to achieve propeller chirality for triarylboranes owing to the low transition barrier between the P and M forms of the boron center. Herein, we report a new strategy to achieve propeller chirality of triarylboranes. It was found that the chirality relay from axially chiral 1,1'-binaphthyl to propeller chirality of the trivalent boron center can be realized when a Me2 N and a Mes2 B group (Mes=mesityl) are introduced at the 2,2'-positions of the 1,1'-binaphthyl skeleton (BN-BNaph) owing to the strong π-π interaction between the Me2 N-bonded naphthyl ring and the phenyl ring of one adjacent Mes group, which not only exerts great steric hindrance on the rotation of the two Mes groups but also gives unequal stability to the two configurations of the boron center for a given configuration of the binaphthyl moiety. The stereostructures of the boron center were fully characterized through 1 H NMR spectroscopy, X-ray crystal analyses, and theoretical calculations. Detailed comparisons with the analog BN-Ph-BNaph, in which the Mes2 B group is separated from 1,1'-binaphthyl by a para-phenylene spacer, confirmed the essential role of π-π interaction for the successful chirality relay in BN-BNaph.

Synthesis and Properties of Benzothieno[b]-Fused BODIPY Dyes.

Two benzothieno[b]-fused BODIPYs, BT-BODIPY and BBT-BODIPY, in which one parent BODIPY core is fused with one and two benzothieno rings, respectively, were synthesized from BODIPYs substituted with 2-(methylsulfinyl)phenyl at the ß-position. The first H2SO4-induced cyclization and deborylation afforded benzothieno[b]-fused dipyrrin derivatives, which can easily complex with BF3·OEt2 to form the desired benzothieno[b]-fused BODIPYs. It was revealed that the fusion of the benzothieno ring is more effective at extending conjugation than simple attachment of the 2-(methylthio)phenyl substituent, which presumably results from conformational restriction. Compared with the corresponding unstrained SPh-BODIPY and BSPh-BODIPY, which contain one and two 2-(methylthio)phenyl groups at the ß-position, BT-BODIPY and BBT-BODIPY display red shifted absorption, increased absorptivity, and fluorescence efficiency. Furthermore, the ring fusion is also helpful to increase stability of the formed cation in BBT-BODIPY. Thus, BBT-BODIPY exhibits very intriguing properties, such as intense absorption and emission in the red region, very sharp emission spectra, and reversible oxidation and reduction potentials.

Charge-Transfer Emission in Organoboron-Based Biphenyls: Effect of Substitution Position and Conformation.

A series of organoboron-based biphenyls o,o'-NMe2, o,p'-NMe2, p,p'-NMe2, which contain an electron-donating NMe2 and an electron-accepting BMes2 groups at o,o'-, o,p'-, p,p'-positions of biphenyl skeleton, respectively, as well as o,o'-NBn2, which contains more bulky NBn2 rather than NMe2, were fully characterized to explore the effect of structural modification on the intramolecular charge-transfer emissions. In addition to significant effect of substitution position on photophysical properties, remarkable influence of conformation was also observed for o,o'-substituted compounds. The emission is substantially blue-shifted as conformation changes from the location of NMe2 and BMes2 at same side of biphenyl axis with a close B···N distance, and thus direct B···N electronic interaction in o,o'-NMe2, to the location of NBn2 and BMes2 on two opposite sides in o,o'-NBn2. And o,o'-NMe2 exhibits the longest emission wavelength, but the shortest absorption wavelength, and thus largest Stokes shift among these four organoboron-based biphenyls in both solution and solid state. The theoretical calculations demonstrated that the unique structure of o,o'-NMe2, in which boryl and amino located at the same side of biphenyl axis with close B···N distance and direct B···N electronic interaction, is helpful to stabilize the lowest singly occupied orbital in the exited state.

A highly selective ratiometric bifunctional fluorescence probe for Hg(2+) and F(-) ions.

A triarylborane derivative BN-S, which contains a Hg(2+)-responsive dithioacetal group and a F(-)-responsive boryl group, has been designed and synthesized via the functionalization of 2-dimesitylboryl-2'-(N,N-dimethylamino)biphenyl core skeleton with a dithioacetal substituent. This compound displays intense intramolecular charge transfer fluorescence, even for its nano-aggregates in water. The Hg(2+)-promoted deprotection of the dithioacetal group and complexation of F(-) with the tri-coordinate boron center cause hypochromism of fluorescence to different extents. And thus BN-S behaves as a promising ratiometric bifunctional fluorescence probe to detect Hg(2+) and F(-) simultaneously. In addition, the detection of Hg(2+) is performable in aqueous medium using its nano-aggregates.

Triarylboranes with a 2-dimesitylboryl-2'-(N,N-dimethylamino)biphenyl core unit: structure-property correlations and sensing abilities to discriminate between F(-) and CN(-) ions.

A series of triarylboranes, in which different substituents are introduced at the para position of the dimethylamino group of a 2-dimesitylboryl-2'-(N,N-dimethylamino)biphenyl core unit, have been comprehensively investigated to explore the effect of structural modification on photophysical properties. The introduction of electron-accepting substituents would facilitate the HOMO→LUMO charge transfer (CT) transition. In contrast, the intramolecular CT transition is significantly prohibited when electron-donating substituents are incorporated. Notably, the HOMO→LUMO CT transition mainly consists of the transition from the electron-donating amino group to an electron acceptor other than boryl when a strong electron acceptor such as the dicyanovinyl group is present. This dicyanovinyl-substituted compound displays sensing abilities to discriminate fluoride and cyanide ions. In solution in THF, the fluoride ions first bind to the boron center, then attack the α-carbon atom of the dicyanovinyl group, whereas the cyanide anion acts on the electron-accepting centers in the reverse sequence. As a result, the absorption and emission change in different manners upon addition of fluoride and cyanide ions.

Solid-state emissive B,S-bridged p-terphenyls: synthesis, properties, and utility as bifunctional fluorescent sensor for Hg2+ and F- ions.

The efficient synthesis has been disclosed to achieve a new class of ladder-type molecules, B,S-bridged p-terphenyls (BS-TPs). Their properties were fully characterized by UV-vis and fluorescence spectroscopy in both solution and solid state, time-resolved fluorescence spectroscopy, DFT theoretical calculations, and cyclic voltammetry. A detailed comparison between anti-BS-TP and its analogue B,N-bridged p-terphenyl (BN-TP) was made to elucidate the effect of displacement of bridging N with S atom on the properties. The introduction of S rather than N atom as bridging atom leads to increased fluorescence efficiency in both solution and solid state as well as enhanced reduction stability. And thus this new class of ladder-type molecules are highly emissive in both solution and solid state and display reversible reduction wave in cyclic voltammograms, denoting their promising potentials as electron-transporting solid-state emitters. In addition, this new class of molecules are capable of detecting F(-) and Hg(2+) with different fluorescence responses, owing to the high Lewis acidity of the B center to coordinate with F(-) anions and the great mercury-philicity of the S center to complex with Hg(2+) cations.

The effect of composition changes on the structure and electronic properties of jamesonite: a DFT study.

Models of jamesonite with different compositions were built by different amounts of Sb or Pb substitution at Fe sites, and their structures and electronic properties were studied using the DFT method. The structure and properties of jamesonite significantly changed after Sb or Pb substitution. The lengths of the Sb-S and Pb-S bonds are larger than those of the corresponding Fe-S bonds of pure jamesonite, and the polarization of iron atoms adjacent to substitute atoms is weakened. After one Sb atom substitution, the S atoms bonded to Sb (substitution atom) gain more charges than those before Sb substitution. The Sb atom has more positive charges than the corresponding Fe atom before Sb substitution. For one Pb substitution system, the electrons transfer from the substituted Pb to adjacent S atoms, and the larger negative charge of the S atoms causes a slightly stronger Pb-S bond. With increasing Sb or Pb content, the electronic structural changes of the adjacent atoms are similar to those of one Sb or Pb substitution. However, the increase of 4-coordination Sb or 4-coordination Pb with the decrease of Fe atom changes the electronic structure of jamesonite, which will change its flotation performance.