Fluorescent Organic π-Radicals Stabilized with Boron: Featuring a SOMO-LUMO Electronic Transition.

We report on the fluorescence properties of a new class of emissive and stable π-radicals that contain a boron atom at a position distant from the radical center. A fully planarized derivative exhibited an intense red fluorescence with high fluorescence quantum yields (ΦF >0.67) even in polar solvents. To elucidate the origin of this phenomenon, we synthesized another boron-stabilized radical that contains a bulky aryl group on the boron atom. A comparison of these derivatives, as well as with conventional donor-π-acceptor (D-π-A)-type emissive π-radicals, unveiled several characteristic features in their photophysical properties. A theoretical analysis revealed that the SOMO-LUMO electronic transition generates an emissive D1 state. Unlike conventional D-π-A-type π-radicals, this state does not undergo significant structural relaxation. The boron-stabilized π-radicals demonstrated promising potential for organic light-emitting diodes as an emitting material.

Prostaglandin-E2 receptor-4 stimulant rescues cardiac malfunction during myocarditis and protects the heart from adverse ventricular remodeling after myocarditis.

Cardioprotective effect of prostaglandin-E2 receptor-4 (EP4) stimulation on the ischemic heart has been demonstrated. Its effect on the heart affected by myocarditis, however, remains uncertain. In this study, we investigated therapeutic effect of EP4 stimulant using a mouse model of autoimmune myocarditis (EAM) that progresses to dilated cardiomyopathy (DCM). EP4 was present in the hearts of EAM mice. Treatment with EP4 agonist (ONO-0260164: 20 mg/kg/day) improved an impaired left ventricular (LV) contractility and reduction of blood pressure on day 21, a peak myocardial inflammation. Alternatively, DCM phenotype, characterized by LV dilation, LV systolic dysfunction, and collagen deposition, was observed on day 56, along with activation of matrix metalloproteinase (MMP)-2 critical for myocardial extracellular matrix disruption, indicating an important molecular mechanism underlying adverse ventricular remodeling after myocarditis. Continued treatment with ONO-0260164 alleviated the DCM phenotype, but this effect was counteracted by its combination with a EP4 antagonist. Moreover, ONO-0260164 inhibited in vivo proteolytic activity of MMP-2 in association with up-regulation of tissue inhibitor of metalloproteinase (TIMP)-3. EP4 stimulant may be a promising and novel therapeutic agent that rescues cardiac malfunction during myocarditis and prevents adverse ventricular remodeling after myocarditis by promoting the TIMP-3/MMP-2 axis.

Investigation of the Lewis acidic behaviour of an oxygen-bridged planarized triphenylborane toward amines and the properties of their Lewis acid-base adducts.

Lewis acid behavior of an oxygen-bridged triphenylborane (1) to amines and the properties of Lewis acid-base adducts of 1 with amines have been investigated. UV-vis titration and 11B NMR experiments showed the formation of Lewis acid-base adducts of 1 with pyridine, DMAP, quinuclidine, and DABCO, respectively (1·amine). X-ray crystallographic analysis revealed that the planar shape of 1 was converted to a bowl shape by the formation of 1·amine. Interestingly, 1·quinuclidine, 12·DABCO, and 1·DABCO exhibited dual emissions. Excitation spectra and photoluminescence decay time measurements suggest that the dual emissions were ascribed to two excited species, i.e., [1·amine]* and [1]* generated by photodissociation in the excited states.

The first synthesis and X-ray crystallographic analysis of an oxygen-bridged planarized triphenylborane.

An oxygen-bridged planarized triphenylborane has been successfully synthesized. X-ray crystallographic analysis revealed that the molecule has a complete planarized structure and the shortest C-B bonds among the triarylboranes synthesized to date.

Synthesis of fluorinated anti-fluorenacenedione and the structural, electronic, and field-effect properties.

Fluorinated anti-fluorenacenedione 6 was newly synthesized by oxidation of a dehydro[12]annulene fused with tetrafluorobenzene 4. X-Ray crystallography of 6 demonstrated a totally planar structure and shorter intramolecular distances for F ... I, F ... O, and I ... O than the corresponding sums of van der Waals (vdW) radii. In the packing structure, molecules are arranged in a pi-stacked motif, and the intermolecular distances between heavy atoms (C ... I, C ... F, C ... O, F ... I, and F ... O) of the adjacent columns are also shorter than the corresponding sums of vdW radii, indicating highly dense packing for the crystal structure of 6. In the 19F NMR spectrum of 6, a signal for the fluorine atom adjacent to iodine exhibited downfield shift by 29-40 ppm as compared with the other three signals. This is attributed to the intramolecular short contact between F and I atoms, which is supposed to cause a donor-acceptor interaction. Cyclic voltammetry of 6 exhibited two reversible reduction waves at E1/2 = -0.91 and -1.45 V vs. Fc/Fc+. A thin film of 6 was prepared by vacuum deposition and was applied to a field-effect transistor (FET) device, which exhibited n-type transistor responses although the mobility was not very high.

Synthesis of oligo(thienylfuran)s with thiophene rings at both ends and their structural, electronic, and field-effect properties.

Oligo(thienylfuran)s with thiophene rings at both ends (SOSOSOS, DE-SOSOS, DH-SOSOS, DE-SOSOSOS, and DH-SOSOSOS; S and O denote thiophene and furan rings, respectively, DE and DH denote diethyl- and dihexyl-substituted, respectively) were newly synthesized by repetitive Stille coupling reactions. The UV/Vis maximum absorptions of the oligomers, SO, SOSO, SOSOS, SOSOSO, and SOSOSOS, exhibited a clear bathochromic shift with increasing number of heterocycles. The value of the oxidation peak potential (E(pa)1) determined by cyclic voltammetry decreased with an increase in the number of heterocycles by 0.06-0.08 V per heterocycle. The crystal-packing structures of DE-SOSOS and DH-SOSOS determined by X-ray crystallography have a herringbone motif and are denser than the reported structures of pentacene and alpha-sexithiophene. The morphologies of thin films prepared by vacuum deposition and spin coating were investigated by atomic force microscopy and X-ray diffraction. Among these films, those of DE-SOSOS and DH-SOSOS exhibited highly ordered arrangements. The devices based on vacuum-deposited and spin-coated films of DE-SOSOS and DH-SOSOS displayed the highest FET mobilities of 10(-2)-10(-3) cm2 V(-1) s(-1) among the oligomers reported in this study.

Synthesis and structural, electronic, and optical properties of oligo(thienylfuran)s in comparison with oligothiophenes and oligofurans.

[structure: see text] Alternate thiophene/furan oligomers having four and six heterocycles, i.e., oligo(thienylfuran) dimer and trimer 2 (n = 4 and 6), were newly synthesized by repetitive Stille coupling reactions. The structural, electronic, and optical properties of these oligomers were investigated by X-ray crystallography (for n = 4), cyclic voltammetry (CV), UV-vis and fluorescence spectroscopy, and DFT calculations, and the results were compared with those of corresponding oligothiophenes (1) and oligofurans (3). The inter-ring torsional energy profiles calculated for bithiophene 1 (n = 2), thienylfuran 2 (n = 2), and bifuran 3 (n = 2) at the B3LYP/6-31G(d) level indicated that the most stable conformers of 2 (n = 2) and 3 (n = 2) are fully coplanar with transoid structure while that of 1 (n = 2) is twisted with a dihedral angle of 158 degrees . In accord with this, X-ray crystallographic analysis of 2 (n = 4) revealed that the pi-conjugated system is nearly planar with the inter-ring C=C-C=C dihedral angles between the thiophene and furan rings of 173.6(7) degrees , -177.0(7) degrees , and 172.6(6) degrees . In the packing structure, these nearly planar molecules are arranged in a herringbone pattern. The CV on a series of oligo(thienylfuran)s 2 showed irreversible oxidation peaks at +0.90, +0.42, and +0.29 V vs Fc/Fc(+) for n = 2, 4, and 6, which were 0.15-0.18 V lower than those for corresponding oligothiophenes 1 and were closer to those for oligofurans 3. On the other hand, the UV-vis spectra of 2 showed the longest wavelength absorption to be almost identical with those of the corresponding 1, and more bathochromically shifted than those of the corresponding 3. The results of CV and UV-vis measurements were supported by DFT calculations (B3LYP/ 6-311+G(2d,p)//B3LYP/6-31G(d)). Thus, oligo(thienylfuran)s 2 have HOMOs which are higher than those of oligothiophenes 1 and close to those of 3, and HOMO-LUMO gaps which are close to those of 1 and smaller than those of 3. In fluorescence spectra, the quantum yield of 2 increased with elongation of the pi-system (n = 2 (3.5%), 4 (19%), 6 (24%)).

Dehydro[12]- and -[18]annulenes fused with tetrafluorobenzene: synthesis, electronic properties, packing structures, and reactivity in the solid state.

Dehydro[12]- and -[18]annulenes 3 and 4 fused with tetrafluorobenzene were newly synthesized by the copper-mediated oxidative coupling of 1,2-diethynyltetrafluorobenzene. The UV-vis spectra of 3 and 4 showed the maximum absorption to be almost identical to that of the corresponding unsubstituted benzodehydro[12]- and -[18]annulenes 1 and 2, respectively, while the reduction waves in cyclic voltammetry observed at potentials of -1.48 and -1.56 V vs Fc/Fc(+) for 3 and 4 were less negative than those for 1 and 2. In agreement with these results, theoretical calculations (B3LYP/6-31G(d)) indicated that the HOMO-LUMO gap is similar for 1 and 3 and for 2 and 4 but that the LUMO levels of 3 and 4 are apparently lowered by the electronegative fluorine substituents. The X-ray crystallography of single crystals grown from 3 (crystal A), 3.C(6)H(6) (crystal B), and a mixture of 1 and 3 (crystal C) demonstrated that the molecules of 3 are stacked in a slanted manner in crystals A and B, while those of 1 and 3 form sandwichlike 1:2 complexes (3.1.3) that are stacked in a columnar arrangement in crystal C. Despite the suitable packing for topochemical polymerization, crystals A-C were quite stable against photochemical reaction. In contrast, differential scanning calorimetry showed that the thermal polymerization occurred explosively at 120-135 degrees C.