Nobuaki Igarashi

Theoretical study of phthalocyanine–fullerene complex for a high efficiency photovoltaic device using ab initio electronic structure calculation

Abstract Many fullerene-based supramolecules have been proposed as potential organic photovoltaic devices, with their electrochemical and photo-electrochemical properties measured under light illumination. Phthalocyanine possesses good electron-donating properties due to its large easily ionised π-electron system, whereas fullerene is good π-electron acceptor which can be connected with other organic molecules. A phthalocyanine–fullerene-based supramolecular system is therefore a potential material candidate for a photovoltaic cell due to its large and flexible absorption combined with electrical properties similar to an inorganic semiconductor. We investigated the geometric and electronic structure of phthalocyanine–fullerene supramolecule using an ab initio quantum mechanical calculation. The results suggest that the lowest unoccupied molecular orbital (LUMO) state of this supramolecule localized on the fullerene and the highest occupied molecular orbital (HOMO) state is localized on half of the phthalocyanine. The energy difference of localized LUMO levels strongly depended on the functional group attached to the phthalocyanine and the structure of the supramolecule.

Terahertz Vibrational Modes of Crystalline Salicylic Acid by Numerical Model Using Periodic Density Functional Theory

The terahertz vibrational modes of crystalline salicylic acid at 1–6 THz were investigated using a vibrational calculation method in which the diagonalization of force constant matrix was estimated by periodic density functional calculations. The result proved sufficient to enable the terahertz vibrational modes to be assigned to lattice modes at 32.2–64.9 cm-1 coupled with translational and rotational modes, intermolecular bending modes at 67.0–132.1 cm-1 including the torsion of carboxyl groups, and out-of-plane intramolecular bending modes at 162.0–175.4 cm-1. The theoretical model presented allows for the interpretation of the terahertz spectra of organic crystals with a hydrogen-bonded dimer lacking the molecular vibrations of a large amplitude, by including effects arising from crystal periodicity.

First Principles Calculation of Terahertz Vibrational Modes of a Disaccharide Monohydrate Crystal of Lactose

First-principles calculations of the crystalline vibrations of a lactose monohydrate crystal in the terahertz (THz) region were performed using periodic density functional theory calculations. The calculated vibrational modes in the THz region were derived from group motions with different sizes: molecules of lactose and crystal water, pyranose rings, and intramolecular frames. The intermolecular modes with large vibrational amplitude of lactose of 17.5–100.6 cm-1 and of crystal-water of 136.1–237.7 cm-1 were clearly separated. This article especially refers to the intermolecular vibrational modes of crystal water with the THz absorption, which provide detectable spectral features of hydrated crystals.

Theoretical Study of Chlorin-Fullerene Supramolecular Complexes for Photovoltaic Devices

The current general trend in the research and development of photovoltaic elements is toward the production of lower cost devices. An encouraging breakthrough in the development of highly efficient materials has been achieved by mixing electron-donor type polymers with suitable electron acceptors. Many fullerene-based supramolecules have been proposed as potential organic photovoltaic devices. We investigate the geometric and electronic structure of a chlorin-fullerene based supramolecular complex which has been proposed as a potential organic photovoltaic device, using first principles calculations. The results suggest that the LUMO state of this supramolecule is localized on the fullerene and that the HOMO state is localized on the chlorin moiety.

Theoretical study of donor–spacer–acceptor structure molecule for use as stable molecular rectifier: geometric and electronic structures

Abstract Recently, molecular electronics has attracted much attention as a ‘post-silicon technology’ for future nanoscale electronic devices. One of the most important elements in molecular electronic devices is the realization of a unimolecular rectifier. In the present study, the geometric and electronic structure of the TTF-derivative (donor)–sigma-bond–TCNQ-derivative (acceptor), a leading candidate for a molecular rectifying device has been investigated theoretically using ab initio quantum mechanical calculations.

Molecular orbital analysis of frontier orbitals for molecular electronics: a case study of unimolecular rectifier and photovoltaic cell

Abstract Recently, unimolecular devices have attracted significant attention as a ‘post-silicon technology’ to enable the fabrication of future nanoscale electronic devices. In this paper, we describe a candidate molecule for a rectifier function using porphyrin polymer and a photovoltaic cell using fullerene-based supramolecule. We have investigated the geometric and electronic structure of these organic molecules using an ab initio quantum mechanical calculation. These results for the porphyrin polymers show that the localization of the unoccupied orbital state on the acceptor moiety mostly depends on their structures. The calculated results for the electronic structure of a naphthalocyanine–fullerene supramolecule manifest that the HOMO’s were localized on the donor sub-unit and the LUMO’s were localized on theacceptor sub-unit.

Theoretical Study on Chlorin-Fullerene Supramolecular Complex for Photovoltaic Device

de,monstrated the possibility of an organic molecule to realizs a &vicer). Since then, in a remarkable series of experimental &monstrations have shown the feasibility of device, such as a molecular rectifier, resonant tunneling diode, and organic solar cell. Photovoltaic device is one of the most important function, bcause development of photovoltaic elements is aiming more low cost, more high efficient, and more environmentally friendly designs. Elecfron fransfer @T) phenomena in biological and artificial molecule systems has been among intensively studied topics over the past &cades2-s). In natural ptotosynthesis applies ET systems, chlorophyll and qrinone moieties are used and the product of this process is conversion of light into usable chemical energy. For the mimicry of a photosynthesis pro@ss, many supramoleculu systems based on donoracoeptor are proposed. Fullerene is a good n+lectron aooeptor and can be chemically bon&d without changes of their electronic properties with other organic molecules. Porphyrin possesses a good elecfron-donating property since its large n+lectron system is easily ionized and chlorin has almost the same cherrical structure as porphyrin. Thus, chlorin-fullerene based supramolecular syste,rn is a potential candidate of material for photovoltaic cell. Recently, Fukuanmi er aI. synthesize the chlorin-fullerene based supramolecules and measure the lifetime of charge-seprated state as well as one electron redox potential for these moleculess). We investigate the stable geometric and electronic structures of chlorin-fullerene complex using ab initio quantum mechanical calculations.