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Organic friction modifiers (FMs) are commonly utilized in lubricants. FM molecules possess a polar head group that interacts with metallic surfaces and aliphatic chains that cohesively interact with neighboring molecules. Under boundary lubrication conditions, as experienced in engine valve trains and cylinders, fluid films are unable to form between metallic surfaces. This results in metal-metal contact. Thus, organic friction modifiers are commonly utilized to reduce friction under these conditions. While efficacious, these molecules are consumed over time owing to engine environments, reducing their effectiveness. To replenish organic friction modifier stocks in base oil lubricants, tertiary ester derivatives of fatty acid-containing dicarboxylic acids were investigated. A series of fatty acid-containing dicarboxylic acids were first developed based on a tartaric acid backbone and their friction modifying capabilities assessed. Coefficient of friction studies illustrated that friction-modifying capabilities were heavily influenced by polar head group type (i.e., carboxylic acid, ester) and chemical bond to tartaric acid (i.e., ester, ether). Thermogravimetric analysis coupled gas-phase Fourier transform infrared spectroscopy revealed that fatty acid-containing dicarboxylic acids degraded into their respective fatty acids at elevated temperatures. Controlled release studies were conducted on a compound modified with thermocleavable esters, and showed sustained friction modifying activity through the course of the entire study. These systems are ideal candidates for the controlled delivery of friction modifiers, which can increase engine efficiency and reduce fuel consumption, effectively reducing vehicle emissions.

The synthesis of conjugated polymers 1–5 functionalized with 4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione in the backbone is reported and their use in the construction of organic solar cells is demonstrated. Increasing the molar ratio of 2,7-dibromo-3,8-dihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione, relative to 4,4′-dihexyl-5,5′-dibromo-2,2′-bithiophene, in the copolymer synthesis significantly lowers the solubility of these polymers. The incorporation of highly conjugated 3,8-dihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione unit into the polymer backbone has been confirmed by UV–vis absorption. The observation of decreasing quantum yield for the emission in the order of 1, 2, 3 is consistent with copolymers with different comonomer content. The power conversion efficiencies of solar cells using blends of these polymers with PCBM ([6,6]-phenyl C61-butyric acid methyl ester) were determined to be 0.11% for polymer 1, 0.33% for 2, and 0.26% for 3, respectively. Under identical white light illumination, the power conversion efficiency of the device based on polymer 2/PCBM as the active layer was three times higher compared to that of device based on polymer 1/PCBM. Owing to the limited solubility and poor film-forming ability of polymer 3, the power conversion efficiency of solar cell based on 3/PCBM blend is lower than that of 2/PCBM blend, but is still larger than that of 1/PCBM blend. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2680–2688, 2008

Two novel polynorbornenes 11 and 12 functionalized with electronically active conjugated oligomer units in the side chain were synthesized by the ring-opening metathesis polymerization (ROMP) method. Both polymers showed good optical characteristics, thermal stability, film-forming properties, and interesting electrochemical properties. The photophysical and redox behaviors of 11 and 12 are markedly different due to variation in the structure of the pendant oligomers. Polymer 11 with phenyl end-capped oligothiophene co-oligomer in the side chain showed much higher stability toward electrochemical oxidation than 12 with a sexithiophene in the side chain. This was demonstrated by in-situ study of the changes in absorption spectra of the polymer films while varying the potential in electrochemical experiments. During the p-doping process, polymer 11 exhibited highly reversible changes in its absorption peaks when monitored at 430 and 650 nm, and the p-doping/dedoping processes can be repeated many cycles. In...

A new class of semi-flexible dendrimers with oligothiophene (OT) arms up to the third generation have been synthesized and investigated. The synthetic methods employed include a combination of palladium-catalyzed Stille cross-coupling reactions for oligothiophenes, Sonogashira cross-coupling reactions for building blocks, and carbodiimide-mediated esterification for building up the various dendrimers. The optical and electrochemical properties of this series of oligothiophenes-based dendrimers are shown to be strongly influenced by their morphologies as demonstrated by their pronounced solvatochromic and thermochromic responses under different environmental conditions. Introducing rigid oligothiophene arms to shape non-persistent ester-linked dendrimers causes higher generation dendrimers (G2 and G3) to exhibit solvatochromism and thermochromism, while their oligomeric counterpart (3b) and lower generation (G1) analogue do not. Spectroscopic changes due to both intramolecular and intermolecular aggregations are observed.

A series of [G1] to [G3]-oligo(dibenzylsulfide) dendrimers containing up to 21 interior dibenzylsulfide moieties was prepared as starting materials toward the syntheses of two new series of oligo(dibenzyl sulfone) and oligo(phenylenevinylene) dendrimers using two different dendrimer-to-dendrimer conversion strategies. The first strategy entailed the interior functionalization of the [G1] to [G3]-oligo(dibenzylsulfide)s to the corresponding [G1] to [G3]-oligo(dibenzyl sulfone)s via hydrogen peroxide oxidation. Successful conversions of up to 21 interior dibenzylsulfide moieties to the corresponding dibenzyl sulfone groups were demonstrated. The second involved the skeletal rearrangements, also named as dendrimer metamorphosis, of the [G1] and [G2]-oligo(dibenzyl sulfone) dendritic backbones to the corresponding [G1] and [G2]-oligo(phenylenevinylene)s dendrimers via the Ramberg-Backlund (RB) reaction. Up to nine RB rearrangements on a dendrimer skeleton were realized and the conversion efficiency of each single RB rearrangement reaction was found to be 96%.

This paper reports detailed synthesis and characterization of polymers with functional groups for chemoselective immobilization. Various types of 1,4-diiodo-2,5-dialkoxybenzene monomers containing hydrophobic and hydrophilic groups with chemoselective functional group pairs were synthesized and copolymerized with 1,2-bis(4-vinylphenyl)ethane by using Heck coupling reaction. It was found that polymers with aldehyde and oxyamine pairs can easily be immobilized layer-by-layer while polymers with ketone functionalities did not afford multilayer deposition. The reproducible deposition process was monitored by UV/vis spectroscopy. Grazing angle reflection−absorption (GARA) FT-IR spectroscopic study confirmed that the multilayer assembly is driven by oxime bond formation. The experimental thickness of each layer was found to be 20 ± 1 A by ellipsometry, somewhat shorter than that of extended side groups estimated by theoretical calculations. Tapping mode atomic force microscopy showed that the polymer multilayer...

A novel ZnPc monomer as well as PPV-ZnPc conjugated polymers have been synthesized and their optical power limiting (OPL) performances toward picosecond laser pulses at 532 nm have been measured. The comparison with the performance of C 60 under the same condition indicates that two of the compounds synthesized outperformed C 60 at picosecond time scale. It was found that conjugated PPV polymers containing a small amount of ZnPc cannot only preserve, but have also showed improvement over the monomer's OPL properties. It is believed that the backbone modification was responsible for the enhanced OPL performance.

A homologous series of fully functionalized regioregular oligo(3-alkylthiophenes) 10−12 bearing a nonlinear optical (NLO) chromophore was synthesized. An alternating sequence of bromination and Stille cross-coupling reactions was developed for the synthesis of these oligomers and regiochemically pure, trimethylsilyl-substituted bithiophene organostannane 2c was utilized as the building block. The resulting materials were shown to form stable amorphous films exhibiting a large photorefractive (PR) effect. Two-beam coupling and degenerate four-wave mixing experiments demonstrate large optical net gain and high diffraction efficiency. It was also found that the PR performance of these oligomers depends on the π-conjugation chain length with an optimized conjugation length.

A comprehensive investigation of the photorefractive properties of an unusual molecular material is reported. This material is a glassy solid that is composed of a multifunctional molecule consisting of a sexithiophene covalently linked with a nonlinear optical chromophore, a methine dye. A net photorefractive gain coefficient of 70.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and a diffraction efficiency of 18.9% (130 \ensuremath{\mu}m thick) were observed. It was found that this material exhibits the competition of complementary holographic gratings that are formed by the space-charge field of two types of photocarriers. Competition of complementary holographic gratings was revealed from the cancellation and revelation of the two types of gratings and is discussed based on a bipolar two-trap photorefractive model. Two transport channels and two trapping centers for photogenerated electrons and holes, respectively, are responsible for the formation of the two complementary gratings. The mobility and the number density of traps for the two types of charged carriers are different; time-of-flight results indicate that the holes have higher mobility than the electrons. A slow, secondary (weak) grating formed by electrons is 180\ifmmode^\circ\else\textdegree\fi{} out of phase with respect to that of the fast, principal one formed by holes. This reduces the net space-charge field, and a cancellation in the index grating was exhibited during the grating formation process. The slow grating could be revealed, and an oscillationlike behavior was shown under the irradiation of a uniform light. The oxidation and reduction potentials of the charge-carrier species explain the microscopic mechanism for the bipolar transport channels. The buildup dynamics of the gratings are discussed in detail.

Linearly-aligned, axially chiral, enantiomerically pure binaphthyl-based oligomers 1 - 3 were synthesized from enantiomerically pure monomer 4 by an oxidative Hay coupling procedure. The higher oligomers exhibited moderate optical rotation enhancement as compared to the lower analogues, but this effect quickly reached a plateau with the tetramer. Cyclic voltammetry studies of these oligomers showed that there was little electronic interactions between the naphthol units.

Optically active, axially chiral binaphthol-based oligomers 2 to 4 were synthesized via Hay's coupling from the monomer 1 . These oligomers exhibited moderate optical rotation enhancement but the effect quickly reaches a plateau with the tetramer 4 .

Polyether dendritic sectors 1–4 from the first to the fourth generations, respectively, were prepared by a convergent approach from readily available 4- tert -butylphenol, phloroglucinol and 1,3-dibromopropane. Using a three-step iterative synthetic sequence involving mono- O -alkylation of [Gn]-OH with excess 1,3-dibromopropane, bis- O -alkylation of the resulting compound with 5-benzyloxyresorcinol 5 followed by hydrogenolysis with palladium catalyst, [G(n+1)]-OH of the next higher generation could be prepared in good yields. These dendritic sectors have good solubility properties and are inert in both acidic and basic media, and do not show any redox behaviour from −2.0 to +1.9 V. Hence they are useful dendritic building blocks for the preparation of functional dendrimers.

This letter reports a series of molecular materials that shows efficient photorefractive effect. The materials which consist of monolithic methine dye molecules can form amorphous films. A net photorefractive gain of 215 cm−1 and a diffraction efficiency of 87.6% at a semiconductor laser wavelength of 780 nm are observed. These materials are the simplest molecular materials and possess the best photorefractive performances. Due to the large photorefractive effect, optical self-defocusing and instability of the laser beam are observed in these materials when the applied electric field is above a threshold.

Linearly-aligned, axially chiral, enantiomerically pure binaphthyl-based oligomers 1 - 3 were synthesized from enantiomerically pure monomer 4 by an oxidative Hay coupling procedure. The higher oligomers exhibited moderate optical rotation enhancement as compared to the lower analogues, but this effect quickly reached a plateau with the tetramer. Cyclic voltammetry studies of these oligomers showed that there was little electronic interactions between the naphthol units.

This paper reports the synthesis and characterization of a new class of diblock copolymers (co-oligomers), rod-rod conjugated diblock copolymers. A general synthetic strategy is outlined, and the structures of the copolymers (oligothiophene-co-oligophenylenevinylene) are fully characterized. It was found that these copolymers exhibit efficient intramolecular energy transfer. An interesting self-assembly ability of these rod--rod copolymers was also revealed.

A new family of organic semiconducting materials (1−4) integrating the structural components of thiophene and fluorene into a single molecular entity was synthesized and characterized. Optical and electrochemical properties of these previously unknown 4,9-dihydro-s-indaceno[1,2-b:5,6-b‘]dithiophene-4,9-dione derivatives were studied in detail. These materials possess unique optical properties with the longest wavelength absorption maxima around 500−800 nm, which gradually reached a saturation limit with the total number of thiophene units approaching eight. They also display dramatic change in the redox properties with increasing conjugation chain lengths. A thin film of oligomer 3 prepared by a solution-casting method showed a well-ordered solid-state structure according to X-ray diffraction analysis.

[reaction: see text] A new polymer with the diphenyl end-capped oligothiophene co-oligomer unit in the side chain was obtained by the ROMP method. The polymer showed good photophysical characteristics, thermal stability, and film-forming properties. A photovoltaic cell fabricated from this polymer showed relatively large open-circuit voltage (V(OC) = 0.7 V), moderate short-circuit current (I(SC) = 0.7 microA/cm(2)), and excellent device stability under ambient conditions.

A highlight of the recent advances in the study of fully functionalized organic photorefractive materials based on polymers, oligomers and small organic molecules is presented.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Photorefractive (PR) materials are multifunctional materials which combine both photoconductivity and electro-optic response to show a new phenomenon: reversible modulation of the index of refraction by light. In the past years, our group has focused on the development of fully functionalized polymers, oligomers and small molecular materials. We have had success in identifying new materials and in gaining understanding in design principles of better materials. Several new PR material systems have been explored, including conjugated PR polymers containing transition metal complexes as photosensitizers, oligothiophene based PR systems and small molecular PR materials containing carbazole and methine dyes. Large net optical gain and minimized phase separation were achieved. The correlation between molecular structure and physical properties is the focal point of this paper.

This report describes synthesis and characterization of a molecular diode based upon a diblock conjugated oligomer system. This system consists of two conjugated blocks with opposite electronic demand. The molecular structure exhibits a built-in electronic asymmetry, much like a semiconductor p-n junction. Electrical measurements by scanning tunneling spectroscopy (STS) clearly revealed a pronounced rectifying effect. Definitive proof for the molecular nature of the rectifying effect in this conjugated diblock molecule is provided by control experiments with a structurally similar reference compound.

The efficiency of photovoltaic devices fabricated from blends of regioregular poly(3-hexylthiophene) and {6,6}-phenyl C61-butyric acid methylester was improved by introducing a thin Au layer and LiF spacer prior to evaporation of Al contacts onto the polymer blend. Using an optimized Au/LiF/Al electrode gave a 20%–30% improved power efficiency over devices with only LiF/Al for AM1.5 irradiation. The increased efficiency is primarily due to the increased photocurrent, and we present spectroscopic data suggesting that this can be ascribed to plasmon enhancement of the polymer absorption by nanotextured Au.

We have synthesized poly(3-hexylthiophene) (P3HT) from initiator monolayers covalently bound to TiO2 nanotubes fabricated inside nanoscale porous aluminum oxide templates. Much larger density of P3HT is achieved than by infiltration of the pores with P3HT synthesized outside the template. In addition, much lower photoluminescence efficiency is observed for the structure where P3HT is grown in-situ, indicating enhanced charge photogeneration efficiency and suggesting this as a promising strategy for fabrication of hybrid organic–inorganic solid state photovoltaics.

This paper reports the synthesis and characterization of a new class of diblock copolymers (co-oligomers), rod-rod conjugated diblock copolymers. A general synthetic strategy is outlined, and the structures of the copolymers (oligothiophene-co-oligophenylenevinylene) are fully characterized. It was found that these copolymers exhibit efficient intramolecular energy transfer. An interesting self-assembly ability of these rod--rod copolymers was also revealed.