Scaling Approach for Intramolecular Magnetic Coupling Constants of Organic Diradicals

The intramolecular magnetic coupling constants (<i>J</i>) of 9 diradicals (<b>i</b>–<b>ix</b>) coupled with an aromatic ring were investigated by means of unrestricted density functional theory (DFT) calculations [UB3LYP/6-311++G­(d,p)]. For these diradicals, a remarkable linear relationship between the calculated and experimental <i>J</i> values was found. In this study, we suggest that the slope (0.380) of the linear relationship can be utilized as a scaling factor for estimating <i>J</i> values. By applying this scaling factor and calculating <i>J</i> values, we could predict the reliable <i>J</i> values of four dithiadiazolyl (<b>DTDA</b>) diradicals coupled with an aromatic ring. It was also found that this scaling scheme shows a dependence on the length of a coupler. Nevertheless, this scaling approach could be used to estimate <i>J</i> values for diverse diradical systems coupled with a particular coupler by DFT calculations

Organic Magnetic Diradicals (Radical–Coupler–Radical): Standardization of Couplers for Strong Ferromagnetism

The intramolecular magnetic coupling constant (<i>J</i>) values of sets of diradicals linked to bis-DTDA, OVER, and NN radicals (DTDA, OVER, and NN groups) through an aromatic coupler were studied by unrestricted density functional theory calculations (UB3LYP/6-311++G­(d,p)). Among 15 aromatic couplers, 9 compounds with an odd number of carbon atoms along its spin coupling path were found to interact ferromagnetically upon coupling with bisradicals while the other 6 couplers with an even number of carbon atoms along its spin coupling path give rise to antiferromagnetic coupling. The overall trends in the strength of magnetic interactions of aromatic couplers were preserved for DTDA, OVER, and NN groups so that the trend can be utilized as an index for the magnetic strength of a given coupler. It was found that the differences in the nucleus-independent chemical shift (NICS), bond order of connecting bonds, and Mulliken atomic spin density at connected atoms between triplet and BS states are closely related to the intramolecular magnetic behavior. 2,4- and 2,5-phosphole couplers exhibit the strongest intramolecular ferromagnetic and antiferromagnetic interactions among 15 aromatic couplers when linked to diverse bisradicals

Catalytic Mechanism for the Ruthenium-Complex-Catalyzed Synthesis of Amides from Alcohols and Amines: A DFT Study

Details of the reaction mechanism for the Ru–PNN pincer complex catalyzed amidation from an alcohol and an amine proposed by Milstein et al. was elucidated using M06 density functional theory calculations. In addition, the bifunctional double hydrogen transfer (BDHT) mechanism for the dehydrogenative oxidation step was investigated for comparison. Finally, the BDHT mechanism was found to be preferred over the β-H elimination pathway that was proposed by Milstein et al. On the basis of the analysis of NBO charges and orbital interactions of intermediates and transition states, we designed a new catalyst with the addition of an electron-donating substituent (−NEt₂), which provided much reduced energy barriers and a lower potential energy surface along both mechanisms

Single Crystalline-Like TiO₂ Nanotube Fabrication with Dominant (001) Facets Using Poly(vinylpyrrolidone) for High Efficiency Solar Cells

The single crystalline-like TiO₂ nanotubes (SC-TiO₂ NTs) are prepared in the anodization process containing poly­(vinylpyrrolidone) (PVP). The PVP in the electrolyte solution functions as a surfactant and controller of the crystal growth. The PVP is favorably adsorbed onto the (001) surfaces rather than onto the (101) facet during the TiO₂ nanotube (TiO₂ NTs) synthesis because of the high absorption energy (81.1 kcal/mol) on the (001) facets. PVP adsorbed (001) facets are protected during the synthesis, and a single crystalline anatase that primarily exposes the (001) plane is prepared. Furthermore, the overall synthetic mechanism of the fabricated crystalline anatase is clarified using computational calculations. It is clear that there is a difference in the binding interactions between the PVP and TiO₂ facets depending on the type of surface. It is concluded that the differences in the binding energies might cause the generation of the SC-TiO₂ NTs with exposed (001) facets. In the photovoltaic performance results, the dye-sensitized solar cells (DSSCs) based on the SC-TiO₂ NTs show higher photocurrent density because of the large amount of adsorbed dye and the high crystallinity in comparison with that of TiO₂ NTs. Because most of the crystalline SC-TiO₂ NTs with the active (001) facets have low recombination sites, this results in the effective charge separation and electron transport in the SC-TiO₂ NTs DSSCs, leading to the high efficiency solar cell devices

Simple but Useful Scheme toward Understanding of Intramolecular Magnetic Interactions: Benzene-Bridged Oxoverdazyl Diradicals

It has recently been shown that the types of intramolecular magnetic interactions of diradical systems can be changed by the types of radical group: syn-group (or α-group) and anti-group (or β-group). The aim of this study is to establish a useful scheme to understand and explain the intramolecular magnetic interactions in diradical systems regardless of radical groups and the topology of a coupler. We investigated the intramolecular magnetic coupling constant (<i>J</i>) of six oxoverdazyl diradicals (<b>i</b>–<b>vi</b>) coupled with a benzene ring based on the unrestricted DFT calculations. On the basis of our results, we devised a simple but useful scheme by combining the spin alternation rule and the concept of radical group classification. Consequently, it was found that the calculated <i>J</i> values and plots of spin density distributions were consistent with our proposed scheme. In addition, we discussed the closed-shell singlet (<b>CS</b>) state and the dihedral angle effect on <i>J</i> values in detail to comprehensively understand the magnetic interactions of diradical systems. Our scheme can provide the basic framework to design future organic high-spin molecules and organic magnetic materials

Coherent Nuclear Wave Packets Generated by Ultrafast Intramolecular Charge-Transfer Reaction

Intramolecular charge-transfer (ICT) dynamics, including reaction coordinates, structural changes, and reaction rate, has been noted experimentally and theoretically. Here we report the ICT dynamics of laurdan investigated by time-resolved fluorescence at extreme time resolution of 30 fs. A single high-frequency coherent nuclear wave-packet motion on the product potential surface is observed through the modulation of the fluorescence intensity in time. Theory and experiment show that this vibrational mode involves large displacement of the carbon atoms in the naphthalene backbone, which indicates that the naphthalene backbone coordinates are strongly coupled to the ICT reaction of laurdan, not the twisting or planarization of the dimethylamino group

When Anatase Nanoparticles Become Bulklike: Properties of Realistic TiO₂ Nanoparticles in the 1–6 nm Size Range from All Electron Relativistic Density Functional Theory Based Calculations

All electron relativistic density functional theory (DFT) based calculations using numerical atom-centered orbitals have been carried out to explore the relative stability, atomic, and electronic structure of a series of stoichiometric TiO₂ anatase nanoparticles explicitly containing up to 1365 atoms as a function of size and morphology. The nanoparticles under scrutiny exhibit octahedral or truncated octahedral structures and span the 1–6 nm diameter size range. Initial structures were obtained using the Wulff construction, thus exhibiting the most stable (101) and (001) anatase surfaces. Final structures were obtained from geometry optimization with full relaxation of all structural parameters using both generalized gradient approximation (GGA) and hybrid density functionals. Results show that, for nanoparticles of a similar size, octahedral and truncated octahedral morphologies have comparable energetic stabilities. The electronic structure properties exhibit a clear trend converging to the bulk values as the size of the nanoparticles increases but with a marked influence of the density functional employed. Our results suggest that electronic structure properties, and hence reactivity, for the largest anatase nanoparticles considered in this study will be similar to those exhibited by even larger mesoscale particles or by bulk systems. Finally, we present compelling evidence that anatase nanoparticles become effectively bulklike when reaching a size of ∼20 nm diameter

Mitochondria-Targeted Reaction-Based Fluorescent Probe for Hydrogen Sulfide

In this study, we developed a turn-on mitochondria-targeting hydrogen sulfide, “<b>probe</b> <b>1</b>”, based on the selective thiolysis of 7-nitro-1,2,3-benzoxadiazole amine moiety attached to the piperazine-based naphthalimide scaffold. <b>Probe</b> <b>1</b> exhibited excellent properties with 68-fold fluorescence enhancement, a low detection limit (2.46 μM), a low cytotoxicity, and a good selectivity toward hydrogen sulfide. The success of intracellular imaging indicated that <b>probe</b> <b>1</b> could be used in further applications for the investigation of biological functions and pathological roles of H₂S in living systems

Photocatalysis by Phenothiazine Dyes: Visible-Light-Driven Oxidative Coupling of Primary Amines at Ambient Temperature

New phenothiazine based organic dyes were prepared for visible-light-driven organic transformations. The 3,7-disubstituted phenothiazine derivatives showed visible light absorption and reversible one-electron oxidation behavior. In the presence of 0.5 mol % of 3,7-disubstituted phenothiazines, primary benzylamines showed oxidative coupling under visible light irradiation from a blue LED. The electronic effect of substituents in phenothiazine dyes was observed in catalytic activities. The mechanistic pathway of oxidative coupling was discussed based on the detection of H₂O₂ after the reaction

In Situ Water-Compatible Polymer Entrapment: A Strategy for Transferring Superhydrophobic Microporous Organic Polymers to Water

Microporous organic polymer nanoparticles bearing tetraphenylethylene moieties (MOPTs) were prepared in the presence of poly­(vinylpyrrolidone) (PVP). The PVP was entrapped into the microporous network of MOPT to form MOPT-P and played the roles of size control, porosity enhancement, and surface property management. MOPT materials without PVP showed superhydrophobicity with a water contact angle of 151°. In comparison, the MOPT-P showed excellent water compatibility. Moreover, due to the aggregation-induced emission property of tetraphenylethylene moieties, the MOPT-P showed emission and excellent emission-based sensing of nitrophenols in water with <i>K</i>_sv values in the range of 1.26 × 10⁴ ∼ 3.37 × 10⁴ M^–1. It is noteworthy that the MOPT-P used water only as a sensing medium and did not require additional organic solvents to enhance water dispersibility of materials. The MOPT-P could be recovered and reused for the sensing at least five times