Kenji Komaguchi

Dye‐Sensitized Solar Cells Based on Donor‐π‐Acceptor Fluorescent Dyes with a Pyridine Ring as an Electron‐Withdrawing‐Injecting Anchoring Group

A new-type of donor-acceptor π-conjugated (D-π-A) fluorescent dyes NI3-NI8 with a pyridine ring as electron-withdrawing-injecting anchoring group have been developed and their photovoltaic performances in dye-sensitized solar cells (DSSCs) are investigated. The short-circuit photocurrent densities and solar energy-to-electricity conversion yields of DSSCs based on NI3-NI8 are greater than those for the conventional D-π-A dye sensitizers NI1 and NI2 with a carboxyl group as the electron-withdrawing anchoring group. The IR spectra of NI3-NI8 adsorbed on TiO(2) indicate the formation of coordinate bonds between the pyridine ring of dyes NI3-NI8 and the Lewis acid sites (exposed Ti(n+) cations) of the TiO(2) surface. This work demonstrates that the pyridine rings of D-π-A dye sensitizers that form a coordinate bond with the Lewis acid site of a TiO(2) surface are promising candidates as not only electron-withdrawing anchoring group but also electron-injecting group, rather than the carboxyl groups of the conventional D-π-A dye sensitizers that form an ester linkage with the Brønsted acid sites of the TiO(2) surface.

Dye-sensitized solar cells based on D-π-A fluorescent dyes with two pyridyl groups as an electron-withdrawing-injecting anchoring group.

D-π-A fluorescent dye with two pyridyl groups as an electron-withdrawing-injecting anchoring group possessing a high coordinate bonding ability to Lewis acid sites on the TiO2 surface, which can lead to high dye loading on the TiO2 film and efficient electron injection, has been developed as a new type of D-π-A dye sensitizer for dye-sensitized solar cells.

Remarkable Charge Separation and Photocatalytic Efficiency Enhancement through Interconnection of TiO2 Nanoparticles by Hydrothermal Treatment.

Although tremendous effort has been directed to synthesizing advanced TiO2 , it remains difficult to obtain TiO2 exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase, rutile, and amorphous TiO2 particles, and photoexcited electron transfer and subsequent charge separation at the anatase-rutile particle interfaces explain its high photocatalytic efficiency. Herein, we report on a facile and rational hydrothermal treatment of P25 to selectively convert the amorphous component into crystalline TiO2 , which is deposited between the original anatase and rutile particles to increase the particle interfaces and thus enhance charge separation. This process produces a new TiO2 exhibiting a considerably enhanced photocatalytic efficiency. This method of synthesizing this TiO2 , inspired by a recently burgeoning zeolite design, promises to make TiO2 applications more feasible and effective.

New molecular design of donor-π-acceptor dyes for dye-sensitized solar cells: control of molecular orientation and arrangement on TiO2 surface

A series of benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type fluorescent dyes OH1, OH2, OH4, OH7, and OH17 with carboxyl groups on different positions of a chromophore skeleton are synthesized and applied to dye-sensitized solar cells (DSSCs) as a new class of donor-π-acceptor (D-π-A) photosensitizers. In the dye OH1, a carboxyl group acts as not only the anchoring group for attachment on TiO2 surface but also the electron acceptor. For OH2, OH4, and OH7, on the other hand, a carboxyl group is an anchoring group, but the electron acceptor is not a carboxyl group but a cyano group. The dye OH17 has two carboxyl groups, which are located at the same positions as those of OH1 and OH7. The absorption and fluorescence spectra and cyclic voltammograms of these fluorescent dyes resemble very well, showing a negligible influence of the position of carboxyl group on photophysical and electrochemical properties of these dyes. When these dyes are used in DSSCs, however, their photovoltaic performances differ considerably. In order to elucidate the difference in the DSSC performance among the five dyes, kinetics of the electron injection from the conduction band of TiO2 to dye cation and to I3− ions in solution were studied by employing the transient absorption spectroscopy and the transient photovoltage technique, respectively. It is found that the charge recombination rate for OH2 is similar to that of OH1 and is much slower than those of OH4 and OH17, consistent with the high short-circuit photocurrent densities for OH1 and OH2. On the basis of the MO calculations (AM1 and INDO/S) and the charge recombination kinetics, the differences of the photovoltaic performances among the five dyes are discussed from the viewpoint of configuration of the dyes adsorbed on TiO2 surface, and a new molecular design for D-π-A dye sensitizers based on a control of molecular orientation and arrangement of dye adsorbed on TiO2 surface is proposed.

Charge carriers in polyaniline film: a correlation between mobility and in-situ ESR measurements

The mobilities of positive charge carriers in polyaniline films measured as a function of oxidation level are discussed with the help of in-situ ESR measurements. Three different processes are found to occur over oxidation levels ranging from 0.1 to 43%. An initial decrease of mobility is followed by a small hump at oxidation levels up to 7%. This mobility change is ascribed to a change in conformation from coil to expanded coil, which is supported by optical absorption spectra. The rise in mobility from an oxidation window of 7 to 36% can be interpreted well in the framework of a polaron lattice model. ESR data provide strong evidence for the transformation between Curie and Pauli spins. The decrease in the mobility above the 36% oxidation level is accounted for in terms of a transition from the emeraldine salt to the base form.

Solvatochromism of novel donor–π–acceptor type pyridinium dyes in halogenated and non-halogenated solvents

Donor–π–acceptor type pyridinium dyes that have been newly synthesized showed bathochromic shift of the absorption band with decreasing dielectric constant (er) of solvent (negative solvatochromism), and the bathochromic shifts in halogenated solvents were larger than those in non-halogenated solvents of similar er values. The influences of halogenated solvents on the large bathochromic shifts are studied on the basis of 1H NMR measurements, semi-empirical molecular calculations (AM1 and INDO/S using the SCRF Onsager model), and absorption spectral measurements of the dyes adsorbed on nanocrystalline TiO2 film immersed in solvents.

Structure and dynamics of the silacyclobutane radical cation, studied by ab initio and density functional theory and electron spin resonance spectroscopy

The geometric structure, the proton isotropic hyperfine coupling constants and temperature dependence of the isotropic hyperfine coupling constants have been investigated for the silacyclobutane radical cation using Mo/ller-Plesset perturbation theory to second order, the coupled cluster approximation and density functional theory. The temperature dependence of the hyperfine coupling constants is explained employing a one-dimensional model for the description of the ring puckering motion. For the geometrical structure the study supports conclusions made in earlier work based on the measurements of the temperature dependence of the electron spin resonance (ESR) spectra, e.g. the silacyclobutane radical cation possesses an asymmetrically distorted C1 structure in which one of the Si–C bonds is considerably elongated, and the ring is puckered. A reassignment of part of the ESR spectrum is obtained on the basis of the theoretical results in combination with experimental measurements of the low temperature dyn...

An asymmetrically distorted structure of the 1-methylsilacyclohexane radical cation : ESR evidence

Abstract Electronic and geometric structure of the 1-methylsilacyclohexane (1-Me-cSiC5) radical cation in a solid perfluoromethylcy-clohexane matrix at low temperature were used studied by ESR spectroscopy with the aid of three selectively deuteriated 1-methyl-silacyclohexanes, 1-Me-cSiC5-2,2- d 2 , 1-Me-cSiC5-2,2,6,6- d 4 , and 1-Me- d 3 -cSiC5. The radical cation was found to have an asymmetrically distorted geometrical structure with one of the SiC bonds elongated with its electronic ground state proposed to be 2 A in C 1 symmetry. This conclusion was derived from an analysis of the temperature -dependent ESR spectra employing a dynamic model of interconversion between two energetically equivalent distorted mirror image structures.

Synthesis and electrical properties of novel oligothiophenes partially containing 3,4-ethylenedioxythiophenes

Five sorts of soluble oligothiophenes (trimer to undecamer) containing 3,4-ethylenedioxythiophene (EDOT) were synthesized, and their optical and electrochemical properties were investigated in relation to the chain length of oligothiophenes and the number of EDOT units. The introduction of the EDOT unit into a main oligothienylene unit induced a red shift of absorption bands and a negative shift of oxidation potentials. The conductivity of an electrochemically oxidized film of undecamer was found to be around 1 S cm−1. A thin-film field effect transistor was preliminary fabricated with neutral undecamer films and the hole mobility was determined.

ESR studies of the effect of zeolite structures on motional dynamics of NO2

Abstract Electron spin resonance (ESR) spectroscopy was used to study the effect of zeolite structure on the motional dynamics of NO 2 adsorbed on the zeolites. The temperature-dependent ESR spectral line shapes were quantitatively analyzed using the slow-motion ESR theory. It was observed that the motional dynamics of NO 2 is strongly dependent on the structure of the zeolite (Beta-type, ZSM-5, mordenite, L-type and ferrierite zeolites). The following important observations were made. (1) In zeolites with similar channel structures, the diffusion rate of NO 2 is proportional to the channel size, and the order of the diffusion rates is Beta-type>ZSM-5>ferrierite and L-type>mordenite. (2) The diffusion of NO 2 is faster in the zeolites with multi-dimensional channels (Beta-type, ZSM-5 and ferrierite) than that in those with uni-dimensional channels (L-type and mordenite).