Intramolecular Electron Transfer in Multi-Redox Systems Based on Cyclic [3]Spirobifluorenylene Compound.

Cyclic [3]spirobifluorenylene with bulky alkyl groups at the ends (1) was designed and synthesized to investigate the electron transfer phenomena in a π-conjugated system including orthogonal π-conjugated chains. The three bifluorenyl units in 1 are conjugated to each other via spiro-conjugation, resulting in the splitting of the HOMO levels to a small extent. Therefore, the SOMO-HOMO gap of the radical cation species is small, which is considered to allow the facile intramolecular electron transfer. The electronic properties of 1 and its partial structures were characterized by absorption and fluorescence measurements and electrochemical analysis. From the electrochemical oxidation, the interchain Coulombic repulsion was observed. In the TD-DFT calculations for the radical cation species of 1, the geometry-featured interchain electronic transitions were visualized by NTO calculations. The radical cation species of 1 generated by chemical oxidation with SbCl5 exhibited a broadened and lower-energy NIR absorption band exceeding 2000 nm. Considering the results of the TD-DFT calculations, the NIR band of the radical cation of 1 was attributed to the intramolecular electron transfer processes among the bifluorenyl units in the macrocycle. ESR experiments also indicated the delocalization of a spin of 1⋅+ in the whole molecule via hole hopping in the ESR time scale at room temperature. This work demonstrates the usefulness of spiro-conjugation as a bridging unit in molecular wires to facilitate smooth electron transfer.

Ultrasonographic images of spina bifida before obstetric anesthesia: a case series.

BACKGROUND: Spina bifida is a relatively common congenital malformation. As the functional prognosis of patients with spina bifida has improved over time, the number of cases resulting in pregnancy and delivery has increased. Lumbar ultrasonography has become a standard and helpful technique before neuraxial anesthesia. We believe that it might be valuable if we use lumbar ultrasonography to evaluate pregnant women with spina bifida before obstetric anesthesia. CASE PRESENTATION: We performed lumbar ultrasonography to evaluate four pregnant women with spina bifida. Patient 1 had no history of surgery. Lumbar radiography before pregnancy showed a bone defect from L5 to the sacrum as a result of incomplete fusion. Magnetic resonance imaging showed a spinal lipoma and a bone defect of the sacrum. Lumbar ultrasonography showed similar findings. We performed general anesthesia for emergency cesarean delivery. Patient 2 underwent surgical repair immediately after birth. Lumbar ultrasonography showed the same bone defect as well as a lipoma beyond the bone defect. We performed general anesthesia for cesarean delivery. Patient 3 had vesicorectal disorders but no prior surgery. Lumbar radiography before pregnancy showed congenital abnormalities such as incomplete fusion, scoliosis, rotation, and a notably small sacrum. Lumbar ultrasonography showed the same bone defect. We performed general anesthesia for cesarean section with no complications. Patient 4 complained of lumbago a few years after her first delivery and received a diagnosis of spina bifida occulta by lumbar radiography, with the incomplete fusion of only the 5th vertebra. Lumbar ultrasonography indicated the same abnormalities. We placed an epidural catheter to avoid the bone abnormality and achieved epidural labor analgesia with no complications. CONCLUSIONS: Lumbar ultrasonography shows anatomic structures easily, safely, and consistently, without X-ray exposure or the need for more expensive modalities. It is a helpful technique to explore anatomic structures potentially complicated by spina bifida before anesthetic procedures.

Comparison between neonatal outcomes of labor and delivery with labor neuraxial analgesia and without analgesia: A propensity score-matched study.

AIM: This single-center observational study aimed to investigate the association between labor neuraxial analgesia (LNA) and neonatal outcomes. METHODS: We conducted a retrospective cohort study at a tertiary perinatal center and included all vaginal deliveries performed between November 2015 and December 2021. Obstetric and neonatal outcomes were compared between deliveries with LNA (LNA group) and without analgesia (control group). Propensity score (PS) matching was used for statistical analysis. RESULTS: We included 2343 singleton deliveries performed in 1367 nulliparous and 976 multiparous women, in whom LNA was induced in 352 and 178 deliveries, respectively. After PS matching, the nulliparous LNA group had a significantly higher incidence of Apgar scores <7 at 1 (7.1% vs. 3.6%, p = 0.0139) and 5 min (2.3% vs. 0.7%, p = 0.0397) and meconium staining (29.8% vs. 23.2%, p = 0.0272) than the nulliparous control group. Other neonatal outcomes, including umbilical artery pH and neonatal intensive care unit admission rate, were comparable between the nulliparous LNA and control groups. No significant differences in neonatal outcomes were seen in multiparous women. Regarding fetal heart rate abnormalities, severe late deceleration (4.8% vs. 1.7%, p = 0.0036) and severe prolonged deceleration (17.0% vs. 11.9%, p = 0.0224) were more common in the nulliparous LNA group than in the nulliparous control group, and the multiparous LNA group exhibited more severe variable deceleration (21.3% vs. 14.3%, p = 0.0485) than the multiparous control group. CONCLUSION: Our findings suggest that LNA is associated with short-term adverse neonatal and obstetric outcomes in vaginal deliveries. LNA should be performed with precautionary measures and adequate medical resources.

A Dicyanomethyl Radical Conjugated with a Pyridylamino Group: Combining Radical-based Dynamic Covalent Chemistry and Coordination Chemistry.

In this work, we aimed to develop a dicyanomethyl radical that undergoes both reversible C-C bond formation/dissociation and metal-ligand coordination reactions to combine dynamic covalent chemistry (DCC) based on organic radicals with coordination chemistry. We have previously reported a dicyanomethyl radical conjugated with a triphenylamine (1⋅) that exhibits a monomer/dimer equilibrium between the σ-bonded dimer (12 ). We designed and synthesized a novel dicyanomethyl radical with a pyridyl group as a coordination point (2⋅) by replacing the phenyl group of 1⋅ with a 3-pyridyl group. We showed that 2⋅ is also in an equilibrium with the σ-bonded dimer (22 ) in solution and has suitable thermodynamic parameters for application in DCC. 22 coordinates to PdCl2 in a 2 : 2 ratio to selectively form a metallamacrocycle (22 )2 (PdCl2 )2 , and its structure was clarified by single crystal X-ray analysis. Variable-temperature NMR, ESR, and electronic absorption measurements revealed that (22 )2 (PdCl2 )2 also undergoes the reversible C-C bond formation/dissociation reaction. Ligand-exchange experiment showed that 22 was liberated from (22 )2 (PdCl2 )2 by the addition of another ligand with a higher affinity for PdII . This work demonstrated that DCC based on dicyanomethyl radicals works orthogonally to metal-ligand coordination reactions.

Synthesis and Electronic Properties of Directly Linked Dihydrodiazatetracene Dimers.

5,12-Dihydro-5,12-diazatetracene (DHDAT) dimers with different substitution patterns are synthesized: a symmetric one with a C-C bond between the monomer units (1) and two asymmetric ones with a C-N bond between the monomer units (2 and 3). The DHDAT units are planar in the C-C linked dimer 1 but perpendicularly oriented in the C-N linked dimers 2 and 3 (from X-ray analysis). The electronic ground-state interaction between the two units is large in 1 and small in 2 and 3. The emission behavior of 3 is different from that of other dimers and its monomer; it displays positive solvatochromism, characteristic for electron donor-acceptor molecules, despite its donor-donor type structure. Compound 3 exhibits a unique multi-step thermochromic emission behavior. The emission behavior is attributed to the asymmetric distribution of the HOMO and LUMO of DHDAT.

Tetrathiafulvalene-Inserted Diphenoquinone: Synthesis, Structure, and Dynamic Redox Property.

A new tetrathiafulvalene (TTF) derivative is synthesized, which is substituted with two phenoxy radicals on one 1,3-dithiole ring, and may have either open-shell diradical or closed-shell extended-quinoidal ground states. X-ray single crystal analysis and NMR measurements prove that this molecule has a closed-shell extended quinoidal structure both in the solid state and in solution. DFT calculations show the donor-acceptor electronic properties of this molecule with a well-separated HOMO-LUMO distribution and a small HOMO-LUMO energy gap. Because of this donor-acceptor character, this molecule gives both the dication and the dianion species by electrochemical oxidation and reduction. Furthermore, during the redox process between the neutral and dication states, this molecule exhibits unique changes in the cyclic voltammogram upon repeating the cycles or varying the scan rate. The observed electrochemical behavior is explained by the conformational changes in the electrochemically generated species, thus indicating that this molecule is classified as a dynamic redox system.

Hash-Mark-Shaped Azaacene Tetramers with Axial Chirality.

The tetramers of azapentacene derivatives with unique hash mark (#)-shaped structures were prepared in a quite facile manner. The #-shaped tetramers are optically active due to possessing extended biaryl skeletons, and the structure of the tetramer composed of four dihydrodiazapentacene (DHDAP) units (1) was investigated as the first example of this kind of molecule. The tetramer 1 showed characteristic chiroptical properties reflecting its orthogonally arranged quadruple DHDAP moieties, as well as redox activity. The solution of enantiopure 1 exhibited intense circularly polarized luminescence (CPL) with a dissymmetry factor of 2.5 × 10-3. The absolute configuration of the enantiomers of 1 was experimentally determined by X-ray crystal analysis for the dication salt of the enantiomer of 1 with SbCl6- counterions. The solutions of enantiopure 12+·2[SbCl6-] also showed NIR circular dichroism (CD) spectra over the entire range from visible to 1100 nm, enabling the modulation of the chiroptical properties by redox stimuli.

Tetraaza[14]- and Octaaza[18]paracyclophane: Synthesis and Characterization of Their Neutral and Cationic States.

Two kinds of aza[1n]paracyclophanes, tetraaza[14]paracyclophane (P4) and octaaza[18]paracyclophane (P8), were synthesized as the smallest and the largest monodisperse macrocyclic oligomers of polyaniline ever made. Herein we report the electronic nature of the cationic species of these two macrocycles with different ring size. By combining ESR spectroscopy and DFT calculations it was suggested that P4·+ was classified as delocalized class III or poised on the class II/III borderline while P8·+ was regarded as a localized class II mixed-valence system. We successfully isolated the dication of P4 as a stable dicationic salt P42+·2[SbF6]-, and the structure of P42+ was determined by X-ray crystal analysis. Variable-temperature NMR measurements for P42+·2[SbF6]- unequivocally showed that P42+ was a 22π electron system with a singlet ground state. The supercharged hexacation of P8 was also isolated as P86+·6[SbCl6]-, and X-ray crystal analysis revealed that P86+ includes one SbCl6- anion in its macrocyclic cavity.

Recognizing Through-Bond and Through-Space Self-Exchange Charge/Spin Transfer Pathways in Bis(triarylamine) Radical Cations with Similar Geometrical Arrangements.

Radical cations of bis(triarylamine)s, 3 and 4, in which the triarylamine redox centers are bridged by an ortho-phenylene and ortho-carborane cluster, respectively, have been prepared to elucidate the difference in intramolecular charge/spin-transfer (ICT/IST) pathway owing to the two different bridging units affording similar geometrical arrangements between the redox centers. Electrochemistry, absorption spectroscopy, VT-ESR spectroscopy, and DFT calculations reveal that 3.+ and 4.+ are classified into class II and class I mixed-valence systems, respectively, and therefore, through-bond and through-space mechanisms are dominant for the ICT/IST phenomena in 3.+ and 4.+ , respectively. Moreover, SQUID measurements for dicationic species provide the fact that virtually no spin-exchange interaction is observed for spins in 42+ , while the antiferromagnetic interaction for spins in 32+ , in accordance with the existence of a conjugation pathway for the ortho-phenylene bridge.

The Divergent Dimerization Behavior of N-Substituted Dicyanomethyl Radicals: Dynamically Stabilized versus Stable Radicals.

Herein, we demonstrate that the dimerization behavior of amine-substituted dicyanomethyl radicals can be switched from σ- to π-dimerization simply by varying the electron-donating substituents. For dicyanomethyl radicals with a 4,4'-ditolylamine (DT. ) or a phenothiazine (PT. ) substituent, the monomeric radical form and the corresponding dimer connected by a reversible C-C bond (σ-dimer) are in equilibrium in solution. On the other hand, the radical with the julolidine skeleton (JD. ) does not undergo σ-dimerization and was isolated as a stable radical in spite of the absence of bulky protecting groups. X-ray single-crystal analysis revealed that JD. forms the π-dimer in the crystalline state, and variable-temperature spectroscopy showed that JD. is in equilibrium with the π-dimer in toluene solution. DFT calculations point to the importance of electrostatic interactions as a driving force for the π-dimerization of JD. because of its polarized structure.

Ferrocene-Substituted Naphthalenediimide with Broad Absorption and Electron-Transport Properties in the Segregated-Stack Structure.

A new naphthalenediimide (NDI) molecule, where two ferrocene (Fc) units were directly attached to both imide nitrogens (Fc-NDI-Fc), was synthesized. The Fc units provide high crystallinity to Fc-NDI-Fc with good solubility to conventional organic solvents. The Fc units also work as electron-donating substituents, in contrast to the electron-deficient NDI unit, resulting in broad charge-transfer absorption of Fc-NDI-Fc from the UV region to 1500 nm in the solid state. The crystal structure analysis revealed that Fc-NDI-Fc formed a segregated-stack structure. The DFT calculation based on the crystal structure showed that the NDI π-orbitals extended over two axes. The extended π-network of the NDI units led to the electron-transport properties of Fc-NDI-Fc, which was confirmed using a flash-photolysis time-resolved microwave conductivity technique.

Synthesis and Characterization of 6,13-Diamino-Substituted Pentacenes.

A series of 6,13-diamino-substituted pentacenes 1 a-d has been prepared and characterized as a new class of pentacene derivatives with strong donor ability and enhanced solubility in common organic solvents. The spectroelectrochemical and DFT studies revealed that the two-electron oxidation process was accompanied by the substantial structural change into a butterfly-like conformation of the pentacene moiety. More importantly, the extent of deformation from the planar pentacene moiety in the dications of 6,13-diaminopentacene is tunable by varying the N-substituents.

N-Substituted Dicyanomethylphenyl Radicals: Dynamic Covalent Properties and Formation of Stimuli-Responsive Cyclophanes by Self-Assembly.

Dynamic covalent bonds and their chemistry have been of particular interest both from a fundamental and materials science aspect. Demonstrated herein is that triphenylamine (TPA) and carbazole (Cz), substituted with a dicyanomethyl radical, are useful motifs for dynamic covalent chemistry as they have the appropriate bond strength between monomer units as well as high stability and synthetic simplicity. TPA and Cz units substituted by two dicyanomethyl radicals formed macrocyclic oligomers classified as novel types of azacyclophanes, and in particular, the TPA-based diradical gave a cyclic dimer in almost quantitative yield. The cyclic oligomers exhibited thermo- and mechanochromic behavior resulting from the generation of radical species by intermonomer C-C bond cleavage.

A facile and versatile approach to double N-heterohelicenes: tandem oxidative C-N couplings of N-Heteroacenes via cruciform dimers.

Novel double N-hetero[5]helicenes that are composed of two nitrogen-substituted heteropentacenes are synthesized by tandem oxidative CN couplings via the cruciform heteropentacene dimers. The developed method is very facile and enables the synthesis of a double helicene in only two steps from commercially available naphthalene derivatives. These double N-hetero[5]helicenes have larger torsion angles in the fjord regions than typical [5]helicenes, and optical/electrochemical measurements revealed a significant increase in the electronic communication between the two heteropentacene moieties of the double helicenes compared with their cruciform dimers. The optical resolution of one of the double helicenes was successfully carried out, and their stability towards racemization was remarkably higher than those of typical [5]helicenes. The synthetic strategy proposed in this paper should be versatile and widely applicable to the preparation of double helicenes from other N-containing π-conjugated planar molecules.

A Triphenylamine with Two Phenoxy Radicals Having Unusual Bonding Patterns and a Closed-Shell Electronic State.

Reported herein is the structure and the electronic properties of a novel triphenylamine derivative having two phenoxy radicals appended to the amino nitrogen atom. X-ray single crystal analysis and the magnetic resonance measurements demonstrates the unexpected closed-shell electronic structure, even at room temperature, of the molecule and two unusual C-N bonds with multiple-bond character. The theoretical calculations support the experimentally determined molecular geometry with the closed-shell electronic structure, and predicted a small HOMO-LUMO gap originating from the nonbonding character of the HOMO. The optical and electrochemical measurements show that the molecule has a remarkably small HOMO-LUMO gap compared with its triphenylamine precursor.

Charge carrier mobility in organic molecular materials probed by electromagnetic waves.

Charge carrier mobility is an essential parameter providing control over the performance of semiconductor devices fabricated using a variety of organic molecular materials. Recent design strategies toward molecular materials have been directed at the substitution of amorphous silicon-based semiconductors; accordingly, numerous measurement techniques have been designed and developed to probe the electronic conducting nature of organic materials bearing extremely wide structural variations in comparison with inorganic and/or metal-oxide semiconductor materials. The present perspective highlights the evaluation methodologies of charge carrier mobility in organic materials, as well as the merits and demerits of techniques examining the feasibility of organic molecules, crystals, and supramolecular assemblies in semiconductor applications. Beyond the simple substitution of amorphous silicon, we have attempted to address in this perspective the systematic use of measurement techniques for future development of organic molecular semiconductors.

Solvent-free synthesis and chiroptical properties of a C-N axially chiral cruciform dimer of benzo[b]phenoxazine.

A novel C-N axially chiral molecule composed of two tert-butyl-substituted benzo[b]phenoxazine (BPO) was synthesized via solvent-free reactions. The absolute configurations of the enantiomers were determined by X-ray single-crystal analysis. The enantiomers had a sufficiently high racemization barrier to ignore racemization at room temperature (149 ± 20 kJ mol-1), and the solutions exhibited dual circularly polarized emissions stemming from fluorescence and phosphorescence of |gCPL| = ca. 1 × 10-3.

Meta-para-linked octaaza[1(8)]cyclophanes and their polycationic states.

Octaazacyclophanes, octaaza[1(8)]m,p,m,p,m,p,m,p-cyclophane (2) and octaaza[1(8)]m,p,p,p,m,p,p,p-cyclophane (3), as ring-size extended congeners of tetraaza[1(4)]m,p,m,p-cyclophane were synthesized, and the electronic states of their polycationic species were investigated by quantum chemical calculations, electrochemical measurements (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)), UV-vis-NIR spectroelectrochemical measurements, and pulsed electron spin resonance (ESR) spectroscopy. These octaazacyclophanes exhibited multiredox activities depending on different linkage patterns along the macrocyclic molecular skeletons, and both molecules were oxidizable up to their respective octacations. Spectroelectrochemical measurements demonstrated that p-phenylenediamine (PD) moieties in 2 could be converted from the semiquinoidal structure to the quinoidal sturcture with increasing oxidation number, whereas higher oxidation states of 3 did not show definite quinoidal deformation of PD moieties. A pulsed ESR spectrum gave evidence about formation of the almost pure spin-triplet state for 3(2+), whereas the high-spin states of 2(2+) and 2(4+) are virtually degenerate with the competing low-spin states even at low temperatures, probably due to the fragility of spin-coupling pathway caused by facile conformational changes.

Redox modulation of para-phenylenediamine by substituted nitronyl nitroxide groups and their spin states.

Three kinds of para-phenylenediamine (PDA) derivatives bearing nitronyl nitroxide (NN) groups were prepared and characterized on the basis of the electrochemical, electron spin resonance (ESR) spectroscopic, absorption spectroscopic, and magnetic susceptibility measurements. It was clarified that the oxidation potential of the central PDA unit is strongly influenced by the numbers of substituted electron-withdrawing NN groups. In addition, the intervalence charge transfer in the central PDA unit was detected in the monocationic states of the PDAs with two NN groups, indicating the coexistence of the localized spins and the delocalized spin on theses molecules. Moreover, pulsed ESR measurements confirmed that the delocalized spin on the central PDA unit and the localized two spins on the NN groups were ferromagnetically coupled in the monocationic states.

Unveiling a new aspect of oxocarbons: open-shell character of 4- and 5-membered oxocarbon derivatives showing near-infrared absorption.

Oxocarbon derivatives consisting of 4- and 5-membered rings, referred to as croconaine and squaraine dyes and regarded as closed-shell molecules, are found to have an intermediate open-shell character from the experimental results of 1H-NMR, ESR spectroscopy, SQUID magnetometric analysis, and X-ray crystallography. We employed two chalcogenopyrylium moieties with O and S chalcogen atoms as substitutions on oxocarbons. The singlet-triplet energy gaps (ΔE S-T) associated with the degree of diradical nature are smaller for croconaines than for squaraines and smaller for thiopyrylium than for pyrylium groups. The diradical nature impacts the electronic transition energy that decreased with a decreasing degree of diradical contribution. They exhibit substantial two-photon absorption in the region over 1000 nm. The diradical character y of the dye was determined experimentally from the observed one- and two-photon absorption peaks and the triplet energy level. The present finding provides new insight into diradicaloids with the contribution of non-Kekulé oxocarbon and also showcases the correlation between the electronic transition energy and their diradical character.