Ken Tokunaga

Metal Dependence of Signal Transmission through MolecularQuantum-Dot Cellular Automata (QCA): A Theoretical Studyon Fe, Ru, and Os Mixed-Valence Complexes

Dynamic behavior of signal transmission through metal complexes [L5M-BL-ML5]5+ (M=Fe, Ru, Os, BL=pyrazine (py), 4,4’-bipyridine (bpy), L=NH3), which are simplified models of the molecular quantum-dot cellular automata (molecular QCA), is discussed from the viewpoint of one-electron theory, density functional theory. It is found that for py complexes, the signal transmission time (tst) is Fe(0.6 fs) < Os(0.7 fs) < Ru(1.1 fs) and the signal amplitude (A) is Fe(0.05 e) < Os(0.06 e) < Ru(0.10 e). For bpy complexes, tst and A are Fe(1.4 fs) < Os(1.7 fs) < Ru(2.5 fs) and Os(0.11 e) < Ru(0.12 e) < Fe(0.13 e), respectively. Bpy complexes generally have stronger signal amplitude, but waste longer time for signal transmission than py complexes. Among all complexes, Fe complex with bpy BL shows the best result. These results are discussed from overlap integral and energy gap of molecular orbitals.

Mono-Hydrogenation of Fullerene Materials: A Density Functional Theory Study on the Properties of Fullerene Mono-Hydrides C60H and C70H

Mono-hydrogenation effect on the properties of fullerenes C60 and C70 was investigated by the density functional theory (B3LYP/6-311G(d, p)). One isomer of C60H and five isomers of C70H were examined, comparing with C60 and C70. Energies of fullerene mono-hydrides (FMH) are smaller than the summation of energy of the fullerene and that of hydrogen atom. Dipole moments of cationic FMH (μ+) are much larger than those of neutral FMH radicals (μ0). Mono-hydrogenation decreases frontier energy gap (ΔE g) and excitation energy (E ex) by about 0.9 eV. The hyperfine coupling constant (a H), spin density (ρ H, ρ C), and reorganization energy (λ) are strongly dependent on the addition position of hydrogen atom.

Tuning of Fullerene Materials for Organic Solar Cells: A Theoretical Study on the Properties of Defect Fullerenes C59 and C69

Hole transport and other fundamental properties of defect fullerenes C59 and C69 were investigated using density functional theory calculations. C59 and C69 isomers without a four-membered ring and three neighboring five-membered rings are generally stable. Formation of a carbon vacancy in C60 and C70 slightly increases the highest occupied molecular orbital energy and greatly decreases the lowest unoccupied molecular orbital energy, so that the energy gap decreases by 1 eV. The reorganization energies of all defect fullerenes are larger than those of the original C60 and C70 because of the localization of injected carriers around the vacancy. The reorganization energy of defect fullerenes is closely related to relaxation of the C–C bond of unsaturated C atoms.

Hydrogenation Effect on Hole-Transport Properties of Fullerene C70: A Density Functional Theory Study on C70H4, C70H6, and C70H8

Reorganization energies λ of isomers of hydrogenated fullerenes, C70H n (n = 4, 6, 8), are investigated by the density functional theory (B3LYP/6–311G**). The smallest value of λ (λ min) of C70H4 is 74 meV and is smaller than those of C70H2 (79 meV) and C60H4 (83 meV). λ min of C70H6 and C70H8 are 72 meV and 74 meV, respectively. Addition of H atoms to [6,6]-ring fusion generally gives smaller λ than that to [5,6]-ring fusion. Hydrogenation can reduce λ min of C70 materials and the result that C70H6 has the smallest λ min is same with the result of hydrogenation of C60.

A Model Study of the Conversion of Energy from a Chemical Reaction into Motion through a Solvation Motor

Molecular dynamics simulations with the explicit simple solvent model are examined to study the conversion of energy from chemical reactions into the motion of a motor molecule due to the solvation change around the reaction site on the motor molecule. Here, the appearance and disappearance of the attractive interaction between a reaction site and solvent molecules are introduced as a “chemical” reaction. Each of the events for the motion of a solvation motor resembles a random walk. However, on average, changes in the solvation structure due to the “chemical” reaction cause the forward motion, and the displacement of the motor becomes larger than the motor size. The motor is accelerated twice. The collision of solvent molecules with the reaction site caused by the appearance of attraction is dominant as the first driving force during the “chemical” reaction period. The second acceleration is driven by the scattering of solvent molecules near the “chemical” reaction site on the motor after the “chemical” ...

Conversion process of chemical reaction into mechanical work through solvation change

Many systems in which the hydrolysis of ATP is finally converted into the mechanical work are known (e.g. actin‐myosin motor protein system). It seems that there are various types of the conversion mechanism. In this work, we examined a possibility of conversion from chemical reaction into mechanical work due to solvation change around the reaction site by using the molecular dynamics simulation (MD) with explicit solvent model. In our model, solvent molecules, S, and a motor (colloidal particle), M, are treated as Lennard‐Jones (LJ) particles. Effect of chemical reaction is taken in the system as the change of LJ potential parameter e between S and M, however the reaction site is restricted on the M. The parameter e is switched to e′ = 1000 e during the reaction (Δt), Fig. (a). Averaged displacement of the motor M is shown in Fig. (b). The motor M is driven by this reaction model, however the direction and efficiency are dependent on the reaction time Δt and the thermodynamic state of the solvent.

Rotational Effect on the One-Dimensional π-Conjugated Polymer

We have investigated the modulation of the physical and electronic properties including their band structure of poly(1,4-phenylene diethynylene-co-9,10-anthracenylene) by the co-axial rotation of π-conjugated polymer chain in the periodic boundary condition framework. The estimated rotational barrier was calculated to 2.38 kcal/mol per cell, suggesting that the aromatic rings of phenylene and anthracenylene were freely rotating each other at the room temperature. On the other hand, bandgap dramatically changes 2.0–3.0 eV by the rotation of aromatic rings. This result suggests that the electronic properties of this polymer should be influenced by rotational effect at the ambient condition.