Synthesis and ring-opening metathesis polymerisation of o-alkoxy benzothiadiazole paracyclophane-1,9-dienes.

ortho-Diethylhexyloxyphenylene benzothiadiazole paracyclophane-1,9-diene as a mixture of diastereomers was synthesized by a sequential benzyne-induced Stevens rearrangement, oxidation and pyrolysis of a dithia[3.3]paracyclophane. Reaction of these highly strained cyclophanedienes with the second generation Grubbs catalyst showed that they can be ring opened to alternating cis,trans-phenylenevinylene polymers. In situ NMR experiments showed that one isomer 8a polymerised to 90% conversion, whereas the other 8b gave only 9% conversion due to steric hindrance on both faces of the alkene bridges of this isomer. The resulting polymers can be readily isomerized in dilute solution using visible light to the all-trans isomer and the optical and electrochemical properties of these polymers were examined by theory and experiment.

Electrolyte-Gated Organic Field-Effect Transistors for Quantitative Monitoring of the Molecular Dynamics of Crystallization at the Solid-Liquid Interface.

Quantitative measurements of molecular dynamics at the solid-liquid interface are of crucial importance in a wide range of fields, such as heterogeneous catalysis, energy storage, nanofluidics, biosensing, and crystallization. In particular, the molecular dynamics associated with nucleation and crystal growth is very challenging to study because of the poor sensitivity or limited spatial/temporal resolution of the most widely used analytical techniques. We demonstrate that electrolyte-gated organic field-effect transistors (EGOFETs) are able to monitor in real-time the crystallization process in an evaporating droplet. The high sensitivity of these devices at the solid-liquid interface, through the electrical double layer and signal amplification, enables the quantification of changes in solute concentration over time and the transport rate of molecules at the solid-liquid interface during crystallization. Our results show that EGOFETs offer a highly sensitive and powerful, yet simple approach to investigate the molecular dynamics of compounds crystallizing from water.

C-H Borylation/Cross-Coupling Forms Twisted Donor-Acceptor Compounds Exhibiting Donor-Dependent Delayed Emission.

Benzothiadiazole (BT) directed C-H borylation using BCl3 , followed by B-Cl hydrolysis and Suzuki-Miyaura cross-coupling enables facile access to twisted donor-acceptor compounds. A subsequent second C-H borylation step provides, on arylation of boron, access to borylated highly twisted D-A compounds with a reduced bandgap, or on B-Cl hydrolysis/cross-coupling to twisted D-A-D compounds. Photophysical studies revealed that in this series there is long lifetime emission only when the donor is triphenylamine. Computational studies indicated that the key factor in observing the donor dependent long lifetime emission is the energy gap between the S1 /T2 excited states, which are predominantly intramolecular charge-transfer states, and the T1 excited state, which is predominantly a local excited state on the BT acceptor moiety.

A General Protocol for the Polycondensation of Thienyl N-Methyliminodiacetic Acid Boronate Esters To Form High Molecular Weight Copolymers.

Thienyl di-N-methyliminodiacetic acid (MIDA) boronate esters are readily synthesized by electrophilic C-H borylation producing bench stable crystalline solids in good yield and excellent purity. Optimal conditions for the slow release of the boronic acid using KOH as the base in biphasic THF/water mixtures enables the thienyl MIDA boronate esters to be extremely effective homo-bifunctionalized (AA-type) monomers in Suzuki-Miyaura copolymerizations with dibromo-heteroarenes (BB-type monomers). A single polymerization protocol is applicable for the formation of five alternating thienyl copolymers that are (or are close analogues of) state of the art materials used in organic electronics. The five polymers were produced in excellent yields and with high molecular weights comparable to those produced using Stille copolymerization protocols. Therefore, thienyl di-MIDA boronate esters represent bench stable and low toxicity alternatives to highly toxic di-trimethylstannyl AA-type monomers that are currently ubiquitous in the synthesis of these important alternating copolymers.

Highly Emissive Far Red/Near-IR Fluorophores Based on Borylated Fluorene-Benzothiadiazole Donor-Acceptor Materials.

Stille, Suzuki-Miyaura and Negishi cross-coupling reactions of bromine-functionalised borylated precursors enable the facile, high yielding, synthesis of borylated donor-acceptor materials that contain electron-rich aromatic units and/or extended effective conjugation lengths. These materials have large Stokes shifts, low LUMO energies, small band-gaps and significant fluorescence emission >700 nm in solution and when dispersed in a host polymer.

Alkyl substituted [2.2]paracyclophane-1,9-dienes.

[2.2]Paracyclophane-1,9-dienes substituted with n-octyl chains have been synthesised from the corresponding dithia[3.3]paracyclophanes using a benzyne induced Stevens rearrangement. The use of 2-(trimethylsilyl)phenyl trifluoromethanesulfonate and tetra-n-butylammonium fluoride as the in situ benzyne source gave significantly improved yields over traditional sources of benzyne and enabled the preparation of n-octyl substituted [2.2]paracyclophane-1,9-dienes on a multi-gram scale.

A comparison of different chemometrics approaches for the robust classification of electronic nose data.

Accurate detection of certain chemical vapours is important, as these may be diagnostic for the presence of weapons, drugs of misuse or disease. In order to achieve this, chemical sensors could be deployed remotely. However, the readout from such sensors is a multivariate pattern, and this needs to be interpreted robustly using powerful supervised learning methods. Therefore, in this study, we compared the classification accuracy of four pattern recognition algorithms which include linear discriminant analysis (LDA), partial least squares-discriminant analysis (PLS-DA), random forests (RF) and support vector machines (SVM) which employed four different kernels. For this purpose, we have used electronic nose (e-nose) sensor data (Wedge et al., Sensors Actuators B Chem 143:365-372, 2009). In order to allow direct comparison between our four different algorithms, we employed two model validation procedures based on either 10-fold cross-validation or bootstrapping. The results show that LDA (91.56% accuracy) and SVM with a polynomial kernel (91.66% accuracy) were very effective at analysing these e-nose data. These two models gave superior prediction accuracy, sensitivity and specificity in comparison to the other techniques employed. With respect to the e-nose sensor data studied here, our findings recommend that SVM with a polynomial kernel should be favoured as a classification method over the other statistical models that we assessed. SVM with non-linear kernels have the advantage that they can be used for classifying non-linear as well as linear mapping from analytical data space to multi-group classifications and would thus be a suitable algorithm for the analysis of most e-nose sensor data.

Malodour classification with low-cost flexible electronics.

Understanding body malodour in a measurable manner is essential for developing personal care products. Body malodour is the result of bodily secretion of a highly complex mixture of volatile organic compounds. Current body malodour measurement methods are manual, time consuming and costly, requiring an expert panel of assessors to assign a malodour score to each human test subject. This article proposes a technology-based solution to automate this task by developing a custom-designed malodour score classification system comprising an electronic nose sensor array, a sensor readout interface and a machine learning hardware fabricated on low-cost flexible substrates. The proposed flexible integrated smart system is to augment the expert panel by acting like a panel assessor but could ultimately replace the panel to reduce the test and measurement costs. We demonstrate that it can classify malodour scores as good as or even better than half of the assessors on the expert panel.

Synthesis and Ring-Opening Metathesis Polymerization of o-Dialkoxy Paracyclophanedienes.

The highly strained ortho-diethylhexyloxy [2.2]paracyclophane-1,9-diene (M1) can be synthesized by ring contraction of a dithia[3.3]paracyclophane using a benzyne-induced Stevens rearrangement. This paracyclophanediene undergoes ring-opening metathesis polymerization to give well-defined 2,3-dialkoxyphenylenevinylene polymers with an alternating cis/trans alkene stereochemistry and controllable molecular weight. Fully conjugated block copolymers with electron-rich and electron-deficient phenylene vinylene polymer segments can be prepared by sequential monomer additions. These polymers can be readily isomerized to the all-trans stereochemistry polymer. The optical and electrochemical properties of these polymers were investigated by theory and experiment.

Modular synthesis of unsymmetrical [1]benzothieno[3,2-b][1]benzothiophene molecular semiconductors for organic transistors.

A modular approach to underexplored, unsymmetrical [1]benzothieno[3,2-b][1]benzothiophene (BTBT) scaffolds delivers a library of BTBT materials from readily available coupling partners by combining a transition-metal free Pummerer CH-CH-type cross-coupling and a Newman-Kwart reaction. This effective approach to unsymmetrical BTBT materials has allowed their properties to be studied. In particular, tuning the functional groups on the BTBT scaffold allows the solid-state assembly and molecular orbital energy levels to be modulated. Investigation of the charge transport properties of BTBT-containing small-molecule:polymer blends revealed the importance of molecular ordering during phase segregation and matching the highest occupied molecular orbital energy level with that of the semiconducting polymer binder, polyindacenodithiophene-benzothiadiazole (PIDTBT). The hole mobilities extracted from transistors fabricated using blends of PIDTBT with phenyl or methoxy functionalized unsymmetrical BTBTs were double those measured for devices fabricated using pristine PIDTBT. This study underscores the value of the synthetic methodology in providing a platform from which to study structure-property relationships in an underrepresented family of unsymmetrical BTBT molecular semiconductors.

Synthesis and ring-opening metathesis of tetraalkoxy-substituted [2.2]paracyclophane-1,9-dienes.

Tetraalkoxy-substituted [2.2]paracyclophane-1,9-dienes can be prepared in three steps from dithia[3.3]paracyclophanes. A mixture of pseudo-geminal and pseudo-ortho diastereomers is produced and the pure compounds can be separated by fractional crystallization. The solid state structures of these diastereomers reveal strongly distorted aromatic rings consistent with high levels of ring strain. Reaction of these diastereomers with the second generation Grubbs catalyst shows that only the pseudo-geminal isomer can be ring opened to give cis,trans-distrylbenzenes. The origin of this selectivity is discussed and the photoisomerization of the as-formed cis,trans-product to the all trans isomer is demonstrated.

Remobilization of residual non-aqueous phase liquid in porous media by freeze-thaw cycles.

The pore-scale behavior of a nonaqueous phase liquid (NAPL) trapped as residual contamination in a porous medium, subject to freeze-thaw cycles, was investigated by X-ray microcomputed tomography. It is shown that freeze-thaw cycles cause significant NAPL remobilization in the direction of the freezing front, due to the rupture and transport of a significant proportion of (supposedly entrapped) larger multipore NAPL ganglia. Significant NAPL remains in place, however, due to substantial ganglion fragmentation into single- and subpore ganglia. The contraction of branched ganglia into more rounded forms, especially near the top surface, is also observed. Three freezing-induced mechanisms are proposed to explain the results. The findings have important implications for NAPL contamination in cold regions, and for the behavior of water-hydrocarbon systems on the Earth and other planets.

Dynamic tomography with a priori information.

We present "dynamic tomography" algorithms that allow for the high-resolution, time-resolved imaging of dynamic (i.e., continuously time evolving) complex systems at existing x-ray micro-CT facilities. The behavior of complex systems is constrained by the underlying physics. By exploiting a priori knowledge of the geometry of the physical process being studied to allow the use of sophisticated iterative reconstruction techniques that incorporate constraints, we improve on current frame rates by at least an order of magnitude. This allows time-resolved imaging of previously intractable processes, such as two-phase fluid flow. We present reconstructions from experimental data collected at the Australian National University x-ray micro-CT facility.

Real-time monitoring of crystallization from solution by using an interdigitated array electrode sensor.

Monitoring crystallization events in real-time is challenging but crucial for understanding the molecular dynamics associated with nucleation and crystal growth, some of nature's most ubiquitous phenomena. Recent observations have suggested that the traditional nucleation model, which describes the nucleus having already the final crystal structure, may not be valid. It appears that the molecular assembly can range during nucleation from crystalline to partially ordered to totally amorphous phases, and can change its structure during the crystallization process. Therefore, it is of critical importance to develop methods that are able to provide real-time monitoring of the molecular interactions with high temporal resolution. Here, we demonstrate that a simple and scalable approach based on interdigitated electrode array sensors (IESs) is able to provide insights on the dynamics of the crystallization process with a temporal resolution of 15 ms.

Organic Semiconductors Processed from Synthesis-to-Device in Water.

Organic semiconductors (OSCs) promise to deliver next-generation electronic and energy devices that are flexible, scalable and printable. Unfortunately, realizing this opportunity is hampered by increasing concerns about the use of volatile organic compounds (VOCs), particularly toxic halogenated solvents that are detrimental to the environment and human health. Here, a cradle-to-grave process is reported to achieve high performance p- and n-type OSC devices based on indacenodithiophene and diketopyrrolopyrrole semiconducting polymers that utilizes aqueous-processes, fewer steps, lower reaction temperatures, a significant reduction in VOCs (>99%) and avoids all halogenated solvents. The process involves an aqueous mini-emulsion polymerization that generates a surfactant-stabilized aqueous dispersion of OSC nanoparticles at sufficient concentration to permit direct aqueous processing into thin films for use in organic field-effect transistors. Promisingly, the performance of these devices is comparable to those prepared using conventional synthesis and processing procedures optimized for large amounts of VOCs and halogenated solvents. Ultimately, the holistic approach reported addresses the environmental issues and enables a viable guideline for the delivery of future OSC devices using only aqueous media for synthesis, purification and thin-film processing.

MEH-PPV by microwave assisted ring-opening metathesis polymerisation.

Excellent control in the synthesis of MEH-PPV can be achieved by microwave assisted, ring-opening metathesis polymerisation (ROMP) of [2.2]paracyclophanedienes.

Phenylenevinylene Block Copolymers via Ring-Opening Metathesis Polymerization.

Fully conjugated block copolymers containing 1,4- and 1,3-phenylenevinylene repeating units can be prepared by the sequential ring opening metathesis polymerization of strained cyclophanedienes, initiated by ruthenium carbene complexes (Grubbs metathesis catalysts). The molecular weight of the constituent blocks can be tightly controlled by changing the catalyst to monomer ratio and the volume fraction of the block copolymers independently tailored by the ratio of the monomers employed. Extensive phase separation between the constituent blocks is observed in thin films of these polymers by atomic force microscopy and efficient energy transfer between blocks containing 1,4- and 1,3-phenylenevinylene units can be seen in the photoluminescence of these materials.

Gas Blow Coating: A Deposition Technique To Control the Crystal Morphology in Thin Films of Organic Semiconductors.

Rapid, large-scale, and low-cost coating methods that enable precise control of the crystal growth of organic semiconductors are essential to deliver high-performance devices that are robust and reproducible. In this work, a novel method is presented based on a gas blow coating technique, enabling the deposition of thin films of organic semiconductors, whose morphology can be optimized by adjusting the deposition parameters. We demonstrate the deposition of aligned single crystals of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) by gas blow coating and their use as active layers in organic field-effect transistor (OFET) devices. The OFETs of TIPS-pentacene and C8-BTBT have charge mobilities of 0.15 and 1.4 cm2 V-1 s-1, respectively, with low threshold voltages and on/off ratios exceeding 105. This coating method can also be extended to polymeric semiconductors: films based on poly(3-hexylthiophene) and poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno[3,2-b]thiophene)] are realized, establishing gas blow coating as a novel and efficient technique for the deposition of thin films of organic semiconductors.

One-Volt, Solution-Processed Organic Transistors with Self-Assembled Monolayer-Ta2O5 Gate Dielectrics.

Low-voltage, solution-processed organic thin-film transistors (OTFTs) have tremendous potential to be key components in low-cost, flexible and large-area electronics. However, for these devices to operate at low voltage, robust and high capacitance gate dielectrics are urgently needed. Herein, the fabrication of OTFTs that operate at 1 V is reported. These devices comprise a solution-processed, self-assembled monolayer (SAM) modified tantalum pentoxide (Ta2O5) as the gate dielectric. The morphology and dielectric properties of the anodized Ta2O5 films with and without n-octadecyltrichlorosilane (OTS) SAM treatment have been studied. The thickness of the Ta2O5 film was optimized by varying the anodization voltage. The results show that organic TFTs gated with OTS-modified tantalum pentoxide anodized at 3 V (d ~7 nm) exhibit the best performance. The devices operate at 1 V with a saturation field-effect mobility larger than 0.2 cm2 V-1 s-1, threshold voltage -0.55 V, subthreshold swing 120 mV/dec, and current on/off ratio in excess of 5 × 103. As a result, the demonstrated OTFTs display a promising performance for applications in low-voltage, portable electronics.

Nanoparticle-polymer photovoltaic cells.

The need to develop and deploy large-scale, cost-effective, renewable energy is becoming increasingly important. In recent years photovoltaic (PV) cells based on nanoparticles blended with semiconducting polymers have achieved good power conversion efficiencies (PCE). All the nanoparticle types used in these PV cells can be considered as colloids. These include spherical, rod-like or branched organic or inorganic nanoparticles. Nanoparticle-polymer PV cells have the long-term potential to provide low cost, high-efficiency renewable energy. The maximum PCE achieved to date is about 5.5%. This value should rise as recently reported theoretical predictions suggest 10% is achievable. However, there are a number of challenges that remain to be overcome. In this review two general types of nanoparticle-polymer PV cells are considered and compared in detail. The organic nanoparticle-polymer PV cells contain fullerene derivatives (e.g., phenyl C61-butyric acid methyl ester, PCBM) or single-walled nanotubes as the nanoparticle phase. The second type is hybrid inorganic nanoparticle-polymer PV cells. These contain semiconducting nanoparticles that include CdSe, ZnO or PbS. The structure-property relationships that apply to both the polymer and nanoparticle phases are considered. The principles underlying nanoparticle-polymer PV cell operation are also discussed. An outcome of consideration of the literature in both areas are two sets of assembly conditions that are suggested for constructing PCBM-P3HT (P3HT is poly(3-hexylthiophene)) or CdSe-P3HT PV cells with reasonable power conversion efficiency. The maximum PCE reported for organic nanoparticle PV cells is about twice that for inorganic nanoparticle-polymer PV cells. This appears to be related to morphological differences between the respective photoactive layers. The morphological differences are attributed to differences in the colloidal stability of the nanoparticle/polymer/solvent mixtures used to prepare the photoactive layers. The principles controlling the colloid stability of the nanoparticle/polymer/solvent mixtures are discussed.