Insulated molecular wire with highly conductive pi-conjugated polymer core.

We have recently developed a new method for synthesizing polyrotaxanes with a high covering ratio, rigidity, photoluminescence efficiency, and solubility in a variety of organic solvents through the polymerization of structurally defined rotaxane monomers. The rigid rodlike structure of the pi-conjugated core polymers in these polyrotaxanes is thought to facilitate the effective transport of charge carriers. Here we applied this method to the synthesis of a polyrotaxane having a poly(phenylene ethynylene) backbone by the Sonogashira copolymerization of a structurally defined rotaxane with a linker molecule.

Organic conducting wire formation on a TiO2 nanocrystalline structure: towards long-lived charge separated systems.

Conjugated polymer monolayers have successfully been fabricated on a TiO(2) nanocrystalline electrode by a lateral intermonomer charge transfer process, extending the photo-induced charge separated state lifetime by a factor of 50-70.

Conformational relaxation of sigma-conjugated polymer radical anion on picosecond scale.

We report the conformational relaxation of poly[bis(p-n-butylphenyl)silane] (PBPS) radical anion measured by near-ultraviolet-enhanced picosecond pulse radiolysis in tetrahydrofuran solutions. The peak shift and increase in optical density of the transient photoabsorption spectra were investigated by kinetic analysis including reactions of PBPS with solvated/presolvated electrons, peak extraction protocol, and diffusion theory, demonstrating the correspondence in the rate constant (5+/-1x10(2) ps) between the peak shift and increase in oscillator strength. The results were examined by density functional theory and molecular dynamics simulations, where the modeled oligosilane radical anion shows more planner conformation relative to its neutral state and a relaxation time of 8 ps.

Noncovalently netted, photoconductive sheets with extremely high carrier mobility and conduction anisotropy from triphenylene-fused metal trigon conjugates.

Supramolecular assembly of small molecules via noncovalent interaction is useful for bottom-up construction of well-defined macroscopic structures. This approach is attracting increasing interest due to its high potential in manufacturing novel molecular electronic and optoelectronic devices. This Article describes the synthesis and functions of a sheet-shaped assembly from novel triphenylene-fused metal trigon conjugates.

The non-covalent assembly of benzene-bridged metallosalphen dimers: photoconductive tapes with large carrier mobility and spatially distinctive conduction anisotropy.

A newly synthesized benzene-bridged metallosalphen dimer tailored with aliphatic chains is demonstrated for the solution-processed assembly of a pi-electronic tape, which shows a large intrinsic carrier mobility, is spatially anisotropic in conduction, forms p- or n-type semiconductors tunable upon doping, is photoconductive and is capable of repetitive switching with large on-off ratios.

Long-lived hole stabilized at a triphenylamine core and shielded by rigid phenylazomethine dendrons: a pulse radiolysis study.

The optical properties and reactivity of one-electron oxidized states (radical cations) of dendrimers are investigated in benzonitrile solutions by nanosecond pulse radiolysis. The hole stabilized at the triphenylamine (TPA) core is effectively shielded by a rigid dendritic phenylazomethine (DPA) shell of four generations, leading to an extension of its lifetime by nearly 2 orders of magnitude in comparison with a core radical cation without dendrons. A continuous red shift of the peak in the photoabsorption spectrum in the visible region and a decrease in the extinction coefficients (oscillator strengths) are found with increasing dendrimer generation number.

Unusual side-chain effects on charge-carrier lifetime in discotic liquid crystals.

When hexa-peri-hexabenzocoronene (HBC) carries paraffinic side chains with ester-ether termini (1a-1c), a hexagonal columnar liquid-crystalline (LC) mesophase forms, which is characterized by a very wide temperature range (ca. 0-300 degrees C). The LC materials from these HBC derivatives show characteristic electronic properties with an extremely long photocarrier lifetime.

Anisotropic electron transport properties in sumanene crystal.

The high electron mobility with large anisotropy was attained in the needle-like single crystal of sumanene, which was indicated by time-resolved microwave conductivity (TRMC) measurement.

Prominent electron transport property observed for triply fused metalloporphyrin dimer: directed columnar liquid crystalline assembly by amphiphilic molecular design.

A triply fused copper porphyrin dimer, when site-specifically modified on its periphery with hydrophobic and hydrophilic wedges (1C12/TEG), self-assembles into a columnar liquid crystalline (LC) mesophase over a wide-temperature range from -17 to 99 degrees C but gives rise to an amorphous solid when modified with only hydrophobic (1C12/C12) or hydrophilic wedges (1TEG/TEG). A LC film of 1C12/TEG displays at 16 degrees C a top-class one-dimensional electron mobility (0.27 cm2/V x s), as evaluated from its maximum flash-photolysis time-resolved microwave conductivity.

Formation of intramolecular poly(4-hydroxystyrene) dimer radical cation.

Poly(4-hydroxystyrene) (PHS) has been used in lithography as a backbone polymer and is also a promising material for extreme-ultraviolet or electron beam lithography. The dynamics of PHS radical cations generated upon exposure to electron beam were investigated. The transient absorption of PHS was observed in the near-infrared region in p-dioxane solutions by pulse radiolysis.

Amphiphilic molecular design as a rational strategy for tailoring bicontinuous electron donor and acceptor arrays: photoconductive liquid crystalline oligothiophene--C60 dyads.

For tailoring solution-processable optoelectronic thin films, a rational strategy with amphiphilic molecular design is proposed. A donor-acceptor dyad consisting of an oligothiophene and C60, when modified with a hydrophilic wedge on one side and a paraffinic wedge on the other (1Amphi), forms over a wide temperature range a photoconducting smectic A liquid crystal having bicontinuous arrays of densely packed donor and acceptor units. In contrast, when modified with only paraffinic wedges (1Lipo), the dyad forms a smectic A liquid crystalline mesophase, which however is poorly conductive.

Superstructure-dependent optical and electrical properties of an unusual face-to-face, pi-stacked, one-dimensional assembly of dehydrobenzo[12]annulene in the crystalline state.

To develop a novel pi-conjugated molecule-based supramolecular assembly, we designed and synthesized trisdehydrotribenzo[12]annulene ([12]DBA) derivative 2 with three carboxyl groups at the periphery. Recrystallization of 2 from DMSO gave a crystal of the solvate 23 DMSO. Crystallographic analysis revealed, to our surprise, that a face-to-face pi-stacked one-dimensional (1D) assembly of 2 was achieved and that the DMSO molecule played a significant role as a "structure-dominant element" in the crystal.

Effect of the heterointerface on transport properties of in situ formed MgO/titanate heterostructured nanowires.

Heterostructured transition metal oxide nanowires are potential candidates to incorporate rich functionalities into nanowire-based devices. Although the oxide heterointerface plays a crucial role in determining the physical properties, the effects of the heterointerface on the oxide nanowire's properties have not been clarified. Here we investigate for the first time the significant role of the heterointerface in determining the transport properties of well-defined MgO/titanate heterostructured nanowires by combining a technique for in situ formation of a oxide heterointerface and microwave conductivity measurement.

Electronegative oligothiophenes fully annelated with hexafluorocyclopentene: synthesis, properties, and intrinsic electron mobility.

Synthesis of hexafluorocyclopenta[c]thiophene-repeated oligothiophenes up to 6-mer has been accomplished. The photophysical and electrochemical properties of these oligomers unambiguously exemplify marked electronegative character without disrupting the effective conjugation. The combination of time-resolved microwave conductivity and transient optical spectroscopy measurements of the 6-mer revealed the intrinsic electron mobility to be as high as 2.

Effects of porphyrin substituents on film structure and photoelectrochemical properties of porphyrin/fullerene composite clusters electrophoretically deposited on nanostructured SnO2 electrodes.

We have systematically examined the substituent effects of meso-tetraphenylporphyrins on film structures and the photoelectrochemical properties of the composite clusters of free-base porphyrin and C(60) electrophoretically deposited on nanostructured SnO(2) electrodes. The photocurrent generation efficiency was found to correlate with the complexation ability of the porphyrin for C(60). Basically, the incident photon-to-current efficiency (IPCE) value was increased with increasing relative amounts of the porphyrin versus C(60) in the films.

Photoconductive coaxial nanotubes of molecularly connected electron donor and acceptor layers.

Controlled self-assembly of a trinitrofluorenone-appended gemini-shaped amphiphilic hexabenzocoronene selectively formed nanotubes or microfibers with different photochemical properties. In these nanotubes, which are 16 nanometers in diameter and several micrometers long, a molecular layer of electron-accepting trinitrofluorenone laminates an electron-donating graphitic layer of pi-stacked hexabenzocoronene. The coaxial nanotubular structure allows photochemical generation of spatially separated charge carriers and a quick photoconductive response with a large on/off ratio greater than 10(4).

Customized morphologies of self-condensed multisegment polymer nanowires.

The direct formation of multisegment nanowires consisting of polymer domains by ion beam irradiation is investigated. Cross-linking reactions in the ion tracks result in localized gelation, giving isolated nanowires on substrates. It is demonstrated that the morphology of the final nanostructure is customized by appropriate selection of the ion fluence, combination of polymers, and the solvent employed for development.

Formation and decay of the triplet excited state of pyridine.

A pulse radiolysis study of the formation and decay of the triplet excited state of liquid pyridine has been performed using quenching techniques. The pyridine triplet excited state is observed with an absorption band at lambda = 310 nm and has a first-order decay with a lifetime of 72 ns. Stern-Volmer plots of the quenching of the pyridine triplet excited state with anthracene, naphthalene, and biphenyl give its yield to be 1.

Photogeneration of charge carriers and their transport properties in poly[bis(p-n-butylphenyl)silane].

The photocarrier generation mechanism and mobility in poly[bis(p-n-butylphenyl)silane] (PBPS) thin films doped with a variety of electron acceptors are studied by time-resolved microwave conductivity (TRMC) measurements. It was found that fullerene is a suitable electron acceptor for PBPS as it provides the highest product of photocarrier generation yield phi and mobility Sigmamu under excitation at 532 and 355 nm. The observed high phiSigmamu value of 4.

Increase in the mobility of photogenerated positive charge carriers in polythiophene.

We report the increase in the mobility of charge carriers in regioregular poly 3-hexyl thiophene (RR-P3HT) films by mixing them with tetracyanoethylene (TCNE), which is examined by in situ time-resolved microwave conductivity (TRMC) and transient optical spectroscopy (TOS). TCNE acts not only as an electron acceptor which increases the number of charge carriers on photoexposure but also as a functional additive which enhances the mobility of the charge carriers. This conclusion was deduced from the results of fluorescence quenching, transient optical absorption and photobleaching, and comparison of the TRMC signal with the TOS signal.

Self-condensed nanoparticles of oligofluorenes with water-soluble side chains.

Self-condensation of the amphiphilic fluorene trimer occurs in the solvent mixture, giving pure "green" fluorescent nanoparticles with controlled radii of 20-100 nm. The origin of the green fluorescence is attributed to the excimer emission via excitation of aggregated dimer structures in the nanoparticles rather than the keto-defects. The present study also suggests the possibility of spectral tuning of emissions from oligofluorene aggregates.

Formation of trimer and dimer radical cations of methyl-substituted benzenes in gamma-irradiated low-temperature matrices.

Dimer and trimer radical cations of benzene, toluene, and xylenes were produced selectively after gamma-irradiation in low-temperature 2-methylpentane matrices with electron scavengers: oxygen (O(2)) and sec-butyl chloride (sec-BuCl). The charge resonance (CR) band of the trimer radical cation (M(3)(+)) produced via the corresponding dimer radical cation (M(2)(+)) is clearly seen in the solution containing O(2) as the temperature increases over a range from 80 to 90 K. In o-xylene solution, a fairly strong and distinct M(3)(+) CR absorption is observed; this is due to the large M(3)(+)/M(2)(+) relative extinction coefficient.

Experimental probe for hyperconjugative resonance contribution in stabilizing the singlet state of 2,2-dialkoxy-1,3-diyls: Regioselective 1,2-oxygen migration.

A detailed study of the regioselectivity of 1,2-oxygen migration was conducted using the unsymmetrically substituted singlet 2,2-dialkoxy-1,3-diarylcyclopentane-1,3-diyls 5. The alkoxy group selectively migrates to the electron-donating p-methoxyphenyl-substituted carbon. The regioselective migration of oxygen clearly indicates a hyperconjugative resonance structure, that is, zwitterionic characteristics, in singlet 2,2-dialkoxy-1,3-diyls.