External Electric Field Effects on Absorption and Fluorescence Spectra of a Fullerene Derivative and Its Mixture with Zinc-Tetraphenylporphyrin Doped in a PMMA Film

Electroabsorption and electrofluorescence spectra of a fullerene derivative, C60(C18)2, and its mixture with zinc-tetraphenylporphyrin (ZnTPP) have been measured by using electric field modulation spectroscopy. The change in dipole moment is significant in the electroabsorption spectra both of C60(C18)2 and of a complex composed of C60(C18)2 and ZnTPP, indicating that the excited states both of C60(C18)2 and of a complex between C60(C18)2 and ZnTPP have a large charge-transfer character. The fluorescence quantum yield of C60(C18)2 decreases in the presence of an electric field, which probably arises from the field-induced acceleration of the intramolecular nonradiative process of C60(C18)2 in the fluorescent state. In a mixture between ZnTPP and C60(C18)2, electrofluorescence spectra show the field-induced enhancement for the fluorescence of ZnTPP and the field-induced de-enhancement for the fluorescence both of C60(C18)2 and of the complex between ZnTPP and C60(C18)2. A theoretical analysis clearly shows that the field-induced enhancement of the ZnTPP fluorescence in a mixture results from the field-induced deceleration of the rate of the electron transfer from the excited ZnTPP to C60(C18)2. The standard free energy gap for the photoinduced electron-transfer process is estimated based on the theoretical simulation of the field-dependent fluorescence intensity

Effects of Fullerene Substituents on Structure and Photoelectrochemical Properties of Fullerene Nanoclusters Electrophoretically Deposited on Nanostructured SnO₂ Electrodes

Two kinds of fullerene derivatives have been designed to examine the effect of the fullerene substituents on the structure and photoelectrochemical properties of fullerene clusters electrophoretically deposited on nanostructured SnO2 electrodes. The cluster sizes increase and the incident photon-to-current efficiencies decrease with introduction of large substituents into C60. The trend for photocurrent generation efficiency as well as surface morphology on the electrode can be explained by the steric bulkiness around the C60 molecules. A C60 molecule with two alkoxy chains is suggested to give a bilayer vesicle structure, irrespective of the hydrophobic nature of both the C60 and alkoxy chain moieties. Such information will be valuable for the design of photoactive molecules, which are fabricated onto electrode surfaces to exhibit high energy conversion efficiency

Comparison of Electrode Structures and Photovoltaic Properties of Porphyrin-Sensitized Solar Cells with TiO₂ and Nb, Ge, Zr-Added TiO₂ Composite Electrodes

Electrode structures and photovoltaic properties of porphyrin-sensitized solar cells with TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were examined to disclose the effects of partial substitution of Ti atom by the other metals in the composite electrodes. The TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were prepared by sol−gel process using laurylamine hydrochloride as a template for the formation of micellar precursors yielding well-defined mesoporous nanocrystalline structures, as in the cases of the formation of silica and titania tubules and nanoparticles by the templating mechanism. The TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were characterized by transmission electron microscopy, BET surface area analysis, X-ray diffraction analysis, Raman spectroscopy, and impedance measurements. The TiO2 anatase nanocrystalline structure is retained after doping a small amount (5 mol %) of Nb, Ge, or Zr into the TiO2 structure, suggesting the homogeneous distribution of the doped metals with replacing Ti atom by the doped metal. The power conversion efficiency of the porphyrin-sensitized solar cells increases in the order Zr-added TiO2 (0.8%) 2 (1.2%) 2 (2.0%) 2 cells (2.4%) under the same conditions. The improvement of cell performance of the Ge-added TiO2 cell results from the negative shift of the conduction band of the Ge-added TiO2 electrode. The Ge-added TiO2 cell exhibited a maximum power conversion efficiency of 3.5% when the porphyrin was adsorbed onto the surface of the Ge-added TiO2 electrode with a thickness of 4 μm in MeOH for 1 h

Directional Electron Transfer in Crystals of [CrCo] Dinuclear Complexes Achieved by Chirality-Assisted Preparative Method

The polarization switching mechanism is used in various devices such as pyroelectric sensors and memory devices. The change in polarization mostly occurs by ion displacement. The development of materials whose polarization switches via electron transfer in order to enhance operation speed is a challenge. We devised a synthetic and crystal engineering strategy that enables the selective synthesis of a [CrCo] heterometallic dinuclear complex with a polar crystal structure, wherein polarization changes stem from intramolecular charge transfer between Co and the ligand. Polarization can be modulated both by visible-light irradiation and temperature change. The introduction of chiral ligands was paramount to the successful polarization switching in the valence tautomeric compound. Mixing Cr and Co complexes with enantiopure chiral ligands resulted in the selective formation of only pseudosymmetric [CrCo] heterometallic complexes. Furthermore, the left-handed chiral ligands preferentially interacted with their right-handed counterparts, enabling molecules to form a polar crystal structure

Directional Electron Transfer in Crystals of [CrCo] Dinuclear Complexes Achieved by Chirality-Assisted Preparative Method

The polarization switching mechanism is used in various devices such as pyroelectric sensors and memory devices. The change in polarization mostly occurs by ion displacement. The development of materials whose polarization switches via electron transfer in order to enhance operation speed is a challenge. We devised a synthetic and crystal engineering strategy that enables the selective synthesis of a [CrCo] heterometallic dinuclear complex with a polar crystal structure, wherein polarization changes stem from intramolecular charge transfer between Co and the ligand. Polarization can be modulated both by visible-light irradiation and temperature change. The introduction of chiral ligands was paramount to the successful polarization switching in the valence tautomeric compound. Mixing Cr and Co complexes with enantiopure chiral ligands resulted in the selective formation of only pseudosymmetric [CrCo] heterometallic complexes. Furthermore, the left-handed chiral ligands preferentially interacted with their right-handed counterparts, enabling molecules to form a polar crystal structure

Directional Electron Transfer in Crystals of [CrCo] Dinuclear Complexes Achieved by Chirality-Assisted Preparative Method

The polarization switching mechanism is used in various devices such as pyroelectric sensors and memory devices. The change in polarization mostly occurs by ion displacement. The development of materials whose polarization switches via electron transfer in order to enhance operation speed is a challenge. We devised a synthetic and crystal engineering strategy that enables the selective synthesis of a [CrCo] heterometallic dinuclear complex with a polar crystal structure, wherein polarization changes stem from intramolecular charge transfer between Co and the ligand. Polarization can be modulated both by visible-light irradiation and temperature change. The introduction of chiral ligands was paramount to the successful polarization switching in the valence tautomeric compound. Mixing Cr and Co complexes with enantiopure chiral ligands resulted in the selective formation of only pseudosymmetric [CrCo] heterometallic complexes. Furthermore, the left-handed chiral ligands preferentially interacted with their right-handed counterparts, enabling molecules to form a polar crystal structure

Photoinduced Charge Carrier Dynamics of Zn−Porphyrin−TiO₂ Electrodes: The Key Role of Charge Recombination for Solar Cell Performance

Time resolved absorption spectroscopy has been used to study photoinduced electron injection and charge recombination in Zn-porphyrin sensitized nanostructured TiO2 electrodes. The electron transfer dynamics is correlated to the performance of dye sensitized solar cells based on the same electrodes. We find that the dye/semiconductor binding can be described with a heterogeneous geometry where the Zn−porphyrin molecules are attached to the TiO2 surface with a distribution of tilt angles. The binding angle determines the porphyrin−semiconductor electron transfer distance and charge transfer occurs through space, rather than through the bridge connecting the porphyrin to the surface. For short sensitization times (1 h), there is a direct correlation between solar cell efficiency and amplitude of the kinetic component due to long-lived conduction band electrons, once variations in light harvesting (surface coverage) have been taken into account. Long sensitization time (12 h) results in decreased solar cell efficiency because of decreased efficiency of electron injection