Control of Crystal Structure and Orientation of Ni(salen) by Epitaxial Growth on Alkali Halide

Thin films of N,N′-bis(salicylaldehydo)ethylenediaminato nickel(II) (Ni(salen)) are fabricated by vacuum epitaxy on (001) surfaces of KBr, KCl, and NaCl substrates and characterized by transmission electron microscopy. Two new monoclinic polymorphs of Ni(salen), β (a = 2.59 nm, b = 1.54 nm, c = 0.670 nm, β = 92.6°) and γ (a = 2.56 nm, b = 0.787 nm, c = 0.743 nm, β = 93.7°), are successfully identified by electron diffractions and high resolution images. The β form is produced on all three substrates by deposition at room temperature, while the γ form is produced on NaCl and KCl at 90 °C. The orientation of these polymorphs is controlled by lattice matching. Although the γ form is energetically favorable with better lattice matching to these substrates, the faster-growing β form is preferentially produced at lower substrate temperature. The polymorphic structure of the deposited film is thus governed by both the substrate surface structure and the growth temperature

Sol−Gel Synthesis of Low-Dimensional Silica within Coordination Nanochannels

Sol−Gel Synthesis of Low-Dimensional Silica within Coordination Nanochannel

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

Electrophoretic Deposition of Single-Walled Carbon Nanotubes Covalently Modified with Bulky Porphyrins on Nanostructured SnO₂ Electrodes for Photoelectrochemical Devices

Single-walled carbon nanotubes (SWNTs) covalently modified with large porphyrin molecules have been prepared to construct photoelectrochemical devices with nanostructured SnO2 electrodes on which the multiporphyrin-linked SWNTs are deposited electrophoretically. The film of the porphyrin-linked SWNTs on the nanostructured SnO2 electrode exhibited an incident photon-to-photocurrent efficiency as high as 4.9% under an applied potential of 0.08 V vs SCE. The more uniform film and moderate photocurrent generation in the porphyrin-linked SWNT devices can be rationalized by the exfoliation abilities of the bulky porphyrins that yield large steric hindrance around the SWNTs. Direct electron injection from the excited states of the SWNTs to the conduction band of the SnO2 electrode is responsible for the photocurrent generation. Despite the efficient quenching of the porphyrin-excited singlet state by the SWNTs in the porphyrin-linked SWNTs, the photocurrent action spectra revealed that the excitation of the porphyrin moieties makes no contribution to the photocurrent generation. The evolution of an exciplex between the porphyrin-excited singlet state and the SWNTs and the subsequent rapid decay to the ground state without generating the charge-separated state is proposed to explain the unusual photoelectrochemical behavior. The results obtained here will provide valuable information on the design of SWNT-based photoelectrochemical devices

Guest-to-Host Transmission of Structural Changes for Stimuli-Responsive Adsorption Property

We show that structural changes of a guest molecule can trigger structural transformations of a crystalline host framework. Azobenzene was introduced into a flexible porous coordination polymer (PCP), and cis/trans isomerizations of the guest azobenzene by light or heat successfully induced structural transformations of the host PCP in a reversible fashion. This guest-to-host structural transmission resulted in drastic changes in the gas adsorption property of the host–guest composite, displaying a new strategy for creating stimuli-responsive porous materials

Dendritic Effects on Structure and Photophysical and Photoelectrochemical Properties of Fullerene Dendrimers and Their Nanoclusters

Multifullerene-terminated dendrimers Gn (n = 1−5) were synthesized and structural, photophysical, and photoelectrochemical properties were studied for the fullerene dendrimers and their nanoclusters. The fullerene dendrimers formed clusters when toluene solutions of the fullerene dendrimers were injected into acetonitrile. Dynamic light scattering and atomic force and scanning electron microscopic measurements on these clusters revealed that the cluster size decreased with increasing the generation number of the dendrimers. The negatively charged clusters were deposited electrophoretically onto a nanostructured SnO2-coated ITO electrode by applying DC voltage to the electrode. Photoelectrochemical measurements were carried out in acetonitrile dissolved 0.5 M LiI and 0.01 M I2 with the standard three electrodes containing the fullerene dendrimer-modified SnO2 working electrode, a platinum wire as a counter electrode, and I-/I3- as a reference electrode. An incident photon-to-photocurrent efficiency of the dendrimer photoelectrochemical devices increased with increasing the generation number. Such a close relationship between the structure and photophysical and photoelectrochemical properties of the fullerene dendrimers and their nanoclusters will provide knowledge of photophysics regarding photoactive molecular assemblies with dendritic architectures

Highly Photoconducting π-Stacked Polymer Accommodated in Coordination Nanochannels

We report on the formation of single poly­(<i>N</i>-vinylcarbazole) (PVCz) chains in one-dimensional channels of [La­(1,3,5-benzenetrisbenzoate)]_<i>n</i>, where the side carbazolyl groups of the confined PVCz are effectively π-stacked. This ideal conformation of PVCz chains in the coordination nanochannels contributed to a drastic increase in hole mobility, which was 5 orders of magnitude higher than that in the bulk state. It is also noteworthy that PVCz isolated from the nanchannels still had a high hole mobility

Supramolecular Donor−Acceptor Heterojunctions by Vectorial Stepwise Assembly of Porphyrins and Coordination-Bonded Fullerene Arrays for Photocurrent Generation

Supramolecular Donor−Acceptor Heterojunctions by Vectorial Stepwise Assembly of Porphyrins and Coordination-Bonded Fullerene Arrays for Photocurrent Generatio

A Photoelectrochemical Device with a Nanostructured SnO₂ Electrode Modified with Composite Clusters of Porphyrin-Modified Silica Nanoparticle and Fullerene

A silica nanoparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode. The quenching of the porphyrin excited singlet state on the silica nanoparticle is suppressed significantly, showing that silica nanoparticles are promising scaffolds for organizing photoactive molecules three-dimensionally in nanometer scale. Marked enhancement of the photocurrent generation was achieved in the present system compared with the reference system, where a gold core was employed as a scaffold of porphyrins instead of a silica nanoparticle. The rather small incident photon-to-current efficiency relative to a similar photoelectrochemical device using a silica microparticle may result from poor electron and hole mobility in the composite film due to poor connection between the composite clusters of a porphyrin-modified silica nanoparticle and C60 in micrometer scale

Retention of Intrinsic Electronic Properties of Soluble Single-Walled Carbon Nanotubes after a Significant Degree of Sidewall Functionalization by the Bingel Reaction

Sidewalls of acid-treated, shortened single-walled carbon nanotubes (SWNTs) with long alkyl chains at the open ends and defect sites have been functionalized by Bingel reaction to examine the structures and spectroscopic properties in detail for the first time. The microwave-assisted Bingel reaction has been successfully applied to the sidewall functionalization of which the reaction rate is ca. 50 times faster than that under the conventional conditions. The degree of the sidewall functionalization (one diester unit per 75−300 carbon atoms of SWNTs) was found to be controllable by changing the output power of the microwave under the same temperature. Atomic force microscopy and transmission electron microscopy showed the progressive exfoliation of the SWNT bundles by the double chemical modification. Resonant Raman and UV−vis−NIR absorption spectroscopies revealed that the electronic properties of SWNT are largely retained after a significant degree of sidewall modification by the Bingel reaction without apparent selective reactivity for metallic and semiconducting SWNTs. This is in remarkable contrast with the conventional sidewall functionalization of SWNTs leading to the loss of their electronic properties (one functional group per 10−100 carbon atoms on the sidewall). Thus, our covalent functionalization methodology can provide SWNT materials with both excellent solubility and inherent electronic properties which are highly desirable in solution-phase processing for the fabrication of SWNT-based molecular devices