Bright Fluorescent p-Phenylene-bridged Triarylmethyl Highly Stable Diradical.

Two units of highly stable luminescent triarylmethyl radical, (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM), were bridged by p-phenylene linker. The photoluminescence quantum yield (PLQY) of PyBTM-PhPyBTM was at most 0.4 % in various organic solvents. Adding two mesityl groups on the terminals did not improve the PLQY. In the MesPyBTM-PhPyBTM-Mes, the mesityl group did not worked as an electron donor unlike the previously reported monoradical MesPyBTM. However, adding two n-hexyl groups on the bridging p-phenylene did greatly improve it, and the PLQY of the PyBTM-(Hex2Ph)PyBTM was 7 % in dichloromethane and acetone, and 12 % in poly(methyl methacrylate) (PMMA) film. Twisting p-phenylene linker by hexyl groups hindered the π-conjugation and suppressed the non-radiative decay of the excited state.

Synthesis of Ce(IV) Heteroleptic Double-Decker Complex with a New Helical Naphthalocyanine as a Potential Gearing Subunit.

This paper describes the synthesis of a cerium(IV)-based molecular gear composed of a thioether functionalized phthalocyanine anchoring ligand, and a helical naphthalocyanine rotating cogwheel functionalized with four carbazoles. The naphthalocyanine ligand 9 was obtained after eleven steps (overall yield of 0.2%) as a mixture of three geometrical isomers, two of which are chiral and exhibit high levels of steric hindrance, as shown by DFT calculations. Their attributions have been made using 1H-NMR based on their different symmetry groups. The ratio of isomers was also determined and the prochiral C4h naphthalocyanine shown to be the major compound (55%). Its heteroleptic complexation with cerium (IV) and the anchoring phthalocyanine ligand 10 gave the targeted molecular gear in a 16% yield.

Straightforward Fabrication of Double Roughness Structures on a Microcrystalline Film of a Diarylethene Derivative.

Double roughness structure mimicking the surface of a lotus leaf was prepared using a newly synthesized diarylethene having a six-membered perfluorocyclohexene ring. The cubic-shaped crystals of the open-ring isomer, with sizes of approximately 7 µm, appeared immediately following solution casting. Upon UV irradiation, each cubic crystal was covered with needle-shaped crystals of the closed-ring isomer to form double roughness structures within 1 h. This structure could bear the continuous impact of water droplets.

Spontaneous Combustion of 2-Bromo-3-Methoxythiophene: A Study on Reaction Pathways and Energetics by Quantum Chemical Calculations.

Reaction pathways and energetics for the dimerization and trimerization reactions of 2-bromo-3-methoxythiophene (2Br-3Met) molecules are investigated using hybrid density functional theory (DFT) calculations to obtain insight into the oligomerization reaction observed in the spontaneous combustion of pure liquid 2Br-3Met. The calculations show that the carbon-bromine bond in a 2Br-3Met molecule elongates easily, and the trans addition of this C-Br bond to a double bond in the neighboring 2Br-3Met molecule occurs easily at room temperature, reflecting the evaluated activation energy of ΔHa = 12.46 kcal/mol (enthalpy) or ΔGa = 35.68 kcal/mol (Gibbs free energy, 298.150 K and 1 atm). The formation process of trimers is calculated in a similar way. A model for the explanation of spontaneous combustion is proposed; large oligomers of the 2Br-3Met molecule are produced spontaneously following the initial formation of dimers or trimers. UV-vis spectra and vibration spectra are obtained for related molecular species, which show reasonable agreement with the experimental results.

Short-term experience with aspiration embolectomy using a ACE68 reperfusion catheter to treat embolic superior mesenteric artery occlusion.

We report the short-term results with aspiration embolectomy using an ACE68 reperfusion catheter to treat patients with acute embolic superior mesenteric artery (SMA) occlusion. Our study included 4 consecutive male patients ranging in age from 72 to 86 years (mean age 79 years). In all patients, the main trunk of the SMA was occluded. The technical success rate was 100% for all procedures. There were no major procedure-related complications. One patient underwent laparotomy with intestinal resection after successful recanalization. No patient reported clinical symptoms of abdominal ischemia at follow-up. Our short-term experience shows that percutaneous aspiration embolectomy using an ACE68 reperfusion catheter is an effective treatment for acute mesenteric ischemia.

Cyclization from Higher Excited States of Diarylethenes Having a Substituted Azulene Ring.

The cyclization reaction of diarylethenes having an azulene ring occurs only via higher excited states. Novel diarylethenes having an azulene ring with a strong donor or acceptor were synthesized and examined in these reactions. A derivative having an electron-donating 1,3-benzodithiol-2-ylidenemethyl group at the 1-position of the azulene ring showed photochromism, whereas neither a derivative having a π-conjugated electron-donating group at the 3-position of the azulene ring nor derivatives having a π-conjugated electron-withdrawing group at the 1- or 3-position of the azulene ring showed any photochromism. The photoreactivities of these compounds were explained by calculating forces and bond orders on the excited states using density functional theory (DFT) and time-dependent (TD)-DFT.

Differentiation between glioblastoma and solitary brain metastasis using neurite orientation dispersion and density imaging.

BACKGROUND AND PURPOSE: Neurite orientation dispersion and density imaging (NODDI) is a new technique that applies a three-diffusion-compartment biophysical model. We assessed the usefulness of NODDI for the differentiation of glioblastoma from solitary brain metastasis. METHODS: NODDI data were prospectively obtained on a 3T magnetic resonance imaging (MRI) scanner from patients with previously untreated, histopathologically confirmed glioblastoma (n = 9) or solitary brain metastasis (n = 6). Using the NODDI Matlab Toolbox, we generated maps of the intra-cellular, extra-cellular, and isotropic volume (VIC, VEC, VISO) fraction. Apparent diffusion coefficient - and fraction anisotropy maps were created from the diffusion data. On each map we manually drew a region of interest around the peritumoral signal-change (PSC) - and the enhancing solid area of the lesion. Differences between glioblastoma and metastatic lesions were assessed and the area under the receiver operating characteristic curve (AUC) was determined. RESULTS: On VEC maps the mean value of the PSC area was significantly higher for glioblastoma than metastasis (P < 0.05); on VISO maps it tended to be higher for metastasis than glioblastoma. There was no significant difference on the other maps. Among the 5 parameters, the VEC fraction in the PSC area showed the highest diagnostic performance. The VEC threshold value of ≥ 0.48 yielded 100% sensitivity, 83.3% specificity, and an AUC of 0.87 for differentiating between the two tumor types. CONCLUSIONS: NODDI compartment maps of the PSC area may help to differentiate between glioblastoma and solitary brain metastasis.

Luminescent Mono-, Di-, and Triradicals: Bridging Polychlorinated Triarylmethyl Radicals by Triarylamines and Triarylboranes.

Up to three polychlorinated pyridyldiphenylmethyl radicals bridged by a triphenylamine carrying electron withdrawing (CN), neutral (Me), or donating (OMe) groups were synthesized and analogous radicals bridged by tris(2,6-dimethylphenyl)borane were prepared for comparison. All compounds were as stable as common closed-shell organic compounds and showed significant fluorescence upon excitation. Electronic, magnetic, absorption, and emission properties were examined in detail, and experimental results were interpreted using DFT calculations. Oxidation potentials, absorption and emission energies could be tuned depending on the electron density of the bridges. The triphenylamine bridges mediated intramolecular weak antiferromagnetic interactions between the radical spins, and the energy difference between the high spin and low spin states was determined by temperature dependent ESR spectroscopy and DFT calculations. The fluorescent properties of all radicals were examined in detail and revealed no difference for high and low spin states which facilitates application of these dyes in two-photon absorption spectroscopy and OLED devices.

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene.

Background: Diarylethenes are well-known photochromic compounds, which undergo cyclization and cycloreversion reactions between open- and closed-ring isomers. Recently, diarylethene derivatives with photoswitchable fluorescent properties were prepared. They are applicable for fluorescence imaging including bio-imaging. On the other hand, a new system called "excited state intramolecular proton transfer (ESIPT)" is reported. In the system, absorption and emission bands are largely separated due to the proton transfer, hence it showed strong fluorescence even in the crystalline state. We aimed to construct the photochromic system incorporating the ESIPT mechanism. Results: A diarylethene incorporating a fluorescent moiety that exhibit ESIPT behavior was prepared. The ESIPT is one of the examples which express the mechanisms of aggregation-induced emission (AIE). This compound emits orange fluorescence with a large Stokes shift derived from ESIPT in aprotic solvents such as THF or hexane, while it exhibits only a photochromic reaction in protic solvents such as methanol. In addition, it shows turn-off type fluorescence switching in an aprotic solvent and in crystals. The fluorescence is quenched as the content of closed-ring isomers increases upon UV light irradiation. Conclusions: A diarylethene containing an ESIPT functional group was prepared. It showed fluorescent turn-off behavior during photochromism in aprotic solvents as well as in crystalline state upon UV light irradiation. Furthermore, it showed AIE in THF/water mixtures with blue-shift of the emission.

Circumventricular organs of human brain visualized on post-contrast 3D fluid-attenuated inversion recovery imaging.

PURPOSE: Although contrast-enhanced three-dimensional T2 fluid-attenuated inversion recovery (3D T2-FLAIR) images are useful for assessing various neuronal diseases, physiological enhancement of the circumventricular organs on the images have not been investigated. We aimed to assess the physiological appearance of the circumventricular organs on contrast-enhanced 3D T2-FLAIR images. METHODS: We studied 3-T MR images of the brain of 30 individuals with no apparent brain abnormalities. In ten areas of the brain, the degree of contrast enhancement on 3D T2-FLAIR and magnetization-prepared rapid gradient-echo (MPRAGE) images was evaluated using a 4-point grading system. The pre- and post-contrast mean contrast ratios (CRs) of the anterior pituitary gland, median eminence, and pineal gland were compared. RESULTS: On post-contrast 3D T2-FLAIR images, marked enhancement was most frequently scored in the median eminence, followed by the choroid plexus, posterior pituitary gland, and pineal gland. In 10 of the 30 cases, the vascular organ of the lamina terminalis and the area postrema were enhanced but the subcommissural organ was not. The difference in the mean pre- and post-contrast CRs of the median eminence and pineal gland was statistically significant, while that of the anterior pituitary gland was not. CONCLUSION: On contrast-enhanced 3D T2-FLAIR images, the circumventricular organs show variable enhancement. Our findings help to recognize physiological and abnormal enhancement of brain structures on contrast-enhanced 3D T2-FLAIR images.

Solvent-Controlled Doublet Emission of an Organometallic Gold(I) Complex with a Polychlorinated Diphenyl(4-pyridyl)methyl Radical Ligand: Dual Fluorescence and Enhanced Emission Efficiency.

A paramagnetic, luminescent organometallic gold(I) complex AuI(C6F5)(PyBTM), where PyBTM is a photostable fluorescent polychlorinated diphenyl(4-pyridyl)methyl radical, was prepared, and its crystal and electronic structures and magnetic and optical properties were investigated. Magnetic studies using electron spin resonance spectroscopy and a superconducting quantum interference device magnetometer indicated the existence of S = 1/2 spin per molecule, with the spin density distributed mainly on the PyBTM ligand. The complex exhibited fluorescence in CHCl3 with emission peak wavelength (λem) of 619 nm and the absolute fluorescence quantum yield (ϕem) of 0.04, confirming that AuI(C6F5)(PyBTM) is the first luminescent organometallic complex with a coordinated luminescent radical. Solvent-dependent unique luminescent characteristics were observed in halogenated solvents (CCl4, CHCl3, CH2Cl2, and ClCH2CH2Cl). ϕem decreased, and λem shifted to longer wavelengths as the polarity (dielectric constant) of the solvent increased. Notably, the complex in CCl4 displayed fluorescence with ϕem = 0.23, which was quite high in radicals, while showed dual fluorescence in CH2Cl2 and ClCH2CH2Cl with lifetimes of around 1 and 7 ns for two emissive components. Density functional theory (DFT) and time-dependent (TD)-DFT calculations indicated that the fluorescence occurred from an interligand charge transfer (CT) excited state in CCl4, in which the C6F5 and PyBTM moieties acted as electron donor and acceptor, respectively, while the fluorescence was centered at the PyBTM ligand in the other three solvents. This method, i.e., the formation of an interligand CT state, to enhance ϕem is distinctly different from the methods reported previously. The present study revealed that a coordination bond is available for forming emissive CT excited states that lead to high ϕem, providing a novel method with greater capability for realizing highly emissive radicals.

Bis(dipyrrinato)zinc(II) Complexes: Emission in the Solid State.

This Communication reports the first observation of solid-state photoluminescence in bis(dipyrrinato)zinc(II) complexes with various substituents. The report discusses the effect of their substituents on their crystal structures and spectroscopic properties. Their meso-aryl groups are revealed to play important roles in the spectroscopic properties in the solid state.

Spin-reconstructed proton-coupled electron transfer in a ferrocene-nickeladithiolene hybrid.

A proton-electron dual-responsive system based on a hybrid of ferrocene and metalladithiolene (1) was developed. The formation of the dithiafulvenium moiety was driven by protonation of the metalladithiolene unit of 1 and by oxidation. The change in the electronic structure caused by the protonation was combined with the redox properties of the two components of 1, generating two radical species with different spin density distributions (3d spin and π spin). Furthermore, a spin-reconstructed proton-coupled electron transfer, i.e., the transformation from 3d spin to π spin accompanied by deprotonation, was achieved by a temperature change, the third external stimulus.

Intramolecular Ferromagnetic Radical-Cu(II) Coupling in a Cu(II) Complex Ligated with Pyridyl-Substituted Triarylmethyl Radicals.

Novel metal complexes M(hfac)2(PyBTM)2 [M = Cu(II), Zn(II); hfac = hexafluoroacetylacetonato; PyBTM = (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical] were prepared. Both hexacoordinated complexes had elongated octahedral geometry, in which two PyBTM molecules coordinated at the equatorial positions in Cu(II)(hfac)2(PyBTM)2 but at the axial positions in Zn(II)(hfac)2(PyBTM)2. Magnetic studies revealed an intramolecular ferromagnetic exchange interaction between the spins on PyBTM and Cu(II) (JCu-R/kB = 47 K) based on the orthogonality of the two spin orbitals.

Enhanced luminescent properties of an open-shell (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical by coordination to gold.

A gold(I) complex containing an open-shell luminescent (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl (PyBTM) radical was prepared. The complex showed fluorescence centered mainly on the coordinated PyBTM ligand. The photophysical and photochemical properties were positively modulated upon coordination to Au(I); the photoluminescence quantum yield, fluorescence wavelength, and the stability in the photoexcited state all increased.

Structures and optical properties of tris(trimethylsilyl)silylated oligothiophene derivatives.

The structures and optical properties of tris(trimethylsilyl)silylated oligothiophenes were examined by spectroscopies, theoretical calculations, and single-crystal X-ray measurements. Bathochromic shift from the original oligothiophenes was observed in the tris(trimethylsilyl)silylated ones, confirming the σ-π conjugation between Si-Si σ bonds and π-orbital. 5,5'-Bis(tris(trimethylsilyl)silyl)-2,2'-bithiophene (Si-T2) showed the highest fluorescence quantum yield (ΦF) both in solution (0.67, excited at 350 nm) and the solid state (0.74, excited at 371 nm). The introduction of tris(trimethylsilyl)silyl groups led to the small nonradiative rate constant of Si-T2, resulting in the high ΦF in the solution state. Si-T2 also exhibited effective σ-π conjugation and poor molecular interaction, which reflected its high ΦF in the solid state. On the contrary, lower ΦF (0.13, excited at 331 nm) in the solid state was observed in the longest oligothiophene examined, 5,5‴-bis(1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilan-2-yl)-2,2':5',2″:5″,2‴-quaterthiophene (Si-T4). Single-crystal X-ray measurement clarified that this compound adopted a zigzag packing structure and a rare syn-anti-syn conformation, which led to the poor σ-π conjugation and the decrease of π-orbital overlap in the solid state.

Regulation of the rate of dinucleation of a monocopper(I) complex containing bipyrimidine rotary units by restricted double pyrimidine rotation.

New copper(I) complexes with coordinated 2-(4'-methyl)pyrimidinyl moieties were fabricated, and the isomerism of their pyrimidine ring linkage was investigated. The ligands bis[2-(diphenylphosphino)phenyl] ether (DPEPhos) and 4,4'-dimethyl-2,2'-bipyrimidine (dmbpm) were used to synthesize a heteroleptic copper(I) complex, [Cu(I)(DPEPhos)(dmbpm)]·BF4 (1·BF4), and a dinuclear copper(I) complex, [(Cu(I))2(DPEPhos)2(µ-dmbmp)](BF4)2 [2·(BF4)2]. The X-ray crystallographic structures, UV-vis absorption spectra, and luminescence properties of the complexes were analyzed. The thermodynamic and kinetic aspects of the isomerism of 1·BF4 were examined by variable-temperature NMR. Double pyrimidine ring rotation was found to be restricted sterically by the bulky DPEPhos ligands. This limited the number of the possible isomers: 1·BF4 showed only isomers with either one (io isomer) or both (oo isomer) of the two methyl groups positioned away from the copper center, while dinuclear 2·(BF4)2 was only found as a symmetric (io-io) isomer, with each of the two methyl groups positioned toward different copper centers. The addition of [Cu(MeCN)2(DPEPhos)] (3·BF4) allowed both isomers of 1·BF4 to form 2·(BF4)2, although at different rates and via different pathways, which were analyzed using time-dependent UV-vis spectroscopy. The io isomer dinucleated more quickly than the oo isomer owing to it being able to form 2·(BF4)2 (i) without bond dissociation and (ii) without a sterically congested ii configuration around the copper center. In contrast, oo-1·BF4 required (i) recombination of the bipyrimidine coordination bonds or (ii) formation of a product with higher thermodynamic energy, unsymmetric (ii-oo) 2·(BF4)2. These findings are interpreted as demonstrating a novel kinetic property: a conversion rate determined by pyrimidine ring inversion.

Luminescence, stability, and proton response of an open-shell (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical.

A luminescent open-shell organic radical with high chemical stability was synthesized. (3,5-Dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) was photoluminescent under various conditions. Fluorescence quantum yields of 0.03, 0.26, and 0.81 (the highest value reported for a stable organic radical) were obtained in chloroform, in poly(methyl methacrylate) film at room temperature, and in an EPA matrix (diethyl ether:isopentane:ethanol) at 77 K, respectively. The photostability of PyBTM is up to 115 times higher than that of the tris(2,4,6-trichlorophenyl)methyl radical, a previously reported luminescent radical. The pyridine moiety of PyBTM acts as a proton coordination site, thereby allowing for control of the electronic and optical properties of the radical by protonation and deprotonation.

Structural modification on copper(I)-pyridylpyrimidine complexes for modulation of rotational dynamics, redox properties, and phototriggered isomerization.

The redox properties of copper pyridylpyrimidine complexes, which undergo linkage isomerism based on pyrimidine ring rotation, were compared under different coordination environments. A newly synthesized compound, [Cu(Mepypm)(L(Mes))]BF4 (1·BF4, Mepypm = 4-methyl-2-(2'-pyridyl)pyrimidine, L(Mes) = 2,9-dimesityl-1,10-phenanthroline) was compared with previously reported complexes of [Cu(MepmMepy)(L(Mes))]BF4 (2·BF4, MepmMepy = 4-methyl-2-(6'-methyl-2'-pyridyl)pyrimidine), Cu(Mepypm)(DPEphos)]BF4 (3·BF4, DPEphos = bis[2-(diphenylphosphino)phenyl]ether), [Cu(Mepypm)(L(Anth))]BF4 (4·BF4, L(Anth) = 2,9-bis(9-anthryl)-1,10-phenanthroline), and [Cu(Mepypm)(L(Macro))]BF4 (5·BF4). Isomer ratios, isomerization dynamics, redox properties, and photoelectron conversion functions varied with the coordination structure. Methyl substituents on the 6-position of the pyridine moiety increased steric repulsion and contributed to quicker rotation, enhanced photoluminescence, and increased photodriven rotational isomerization.

Amplification of luminescence of stable radicals by coordination to NHC-gold(I) complex.

The luminescence of stable radicals can be enhanced by coordination to metal complexes. The 4% fluorescence quantum yield of (3,5-difluoro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (F2PyBTM) in dichloromethane was enhanced up to 36% by coordination to AuI with N-heterocyclic carbene ligand, which is a record for metal-radical complexes.