New cancer therapy uses nanoparticles to reprogram immune cells

(Nanowerk News) Researchers at the University of  Georgia are developing a new treatment technique that uses nanoparticles to  reprogram immune cells so they are able to recognize and attack cancer. The  findings were published recently in the early online edition of ACS  Nano (“Ex Vivo Programming of Dendritic Cells by  Mitochondria-Targeted Nanoparticles to Produce Interferon-Gamma for Cancer  Immunotherapy”).

The human body operates under a constant state of martial law.  Chief among the enforcers charged with maintaining order is the immune system, a  complex network that seeks out and destroys the hordes of invading bacteria and  viruses that threaten the organic society as it goes about its work.

The immune system is good at its job, but it’s not perfect. Most  cancerous cells, for example, are able to avoid detection by the immune system  because they so closely resemble normal cells, leaving the cancerous cells free  to multiply and grow into life-threatening tumors while the body’s only  protectors remain unaware.

“What we are working on is specifically geared toward breast  cancer,” said Dhar, the study’s co-author and an assistant professor of  chemistry in the UGA Franklin College of Arts and Sciences. “Our paper reports  for the first time that we can stimulate the immune system against breast cancer  cells using mitochondria-targeted nanoparticles and light using a novel  pathway.”

In their experiments, Dhar and her colleagues exposed cancer  cells in a petri dish to specially designed nanoparticles 1,000 times finer than  the width of a human hair. The nanoparticles invade the cell and penetrate the  mitochondria?the organelles responsible for producing the energy a cell needs to  grow and replicate.

They then activated the nanoparticles inside the cancer cells by  exposing them to a tissue-penetrating long wavelength laser light. Once  activated, the nanoparticles disrupt the cancer cell’s normal processes,  eventually leading to its death.

The dead cancer cells were collected and exposed to dendritic  cells, one of the core components of the human immune system. What the  researchers saw was remarkable.

“We are able to potentially overcome some of the traditional  drawbacks to today’s dendritic cell immunotherapy,” said Sean Marrache, a  graduate student in Dhar’s lab. “By targeting nanoparticles to the mitochondria  of cancer cells and exposing dendritic cells to these activated cancer cells, we  found that the dendritic cells produced a high concentration of chemical signals  that they normally don’t produce, and these signals have traditionally been  integral to producing effective immune stimulation.”

Dhar added that the “dendritic cells recognized the cancer as  something foreign and began to produce high levels of interferon-gamma, which  alerts the rest of the immune system to a foreign presence and signals it to  attack. We basically used the cancer against itself.”

She cautions that the results are preliminary, and the approach  works only with certain forms of breast cancer. But if researchers can refine  the process, this technology may one day serve as the foundation for a new  cancer vaccine used to both prevent and treat disease.

“We particularly hope this technique could help patients with  advanced metastatic disease that has spread to other parts of the body,” said  Dhar, who also is a member of the UGA Nanoscale Science and Engineering Center,  Cancer Center and Center for Drug Discovery.

If the process were to become a treatment, doctors could biopsy  a tumor from the patient and kill the cancerous cells with nanoparticles. They  could then produce activated dendritic cells in bulk quantities in the lab under  controlled conditions before the cells were injected into the patient.

Once in the bloodstream, the newly activated cells would alert  the immune system to the cancer’s presence and destroy it.

“These are the things we can now do with nanotechnology,” Dhar  said. “If we can refine the process further, we may be able to use similar  techniques against other forms of cancer as well.”

Source: University of Georgia

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(Solar) Cell a Million?

SOLAR cells were once a bespoke product, reserved for satellites and military use. In 1977 a watt of solar generating capacity cost $77. That has now come down to about 80 cents, and solar power is beginning to compete with the more expensive sort of conventionally generated electricity. If the price came down further, though, solar might really hit the big time—and that is the hope of Henry Snaith, of Oxford University, and his colleagues. As he described recently in Science, Dr Snaith plans to replace silicon, the material used to make most solar cells, with a substance called a perovskite. This, he believes, could cut the cost of a watt of solar generating capacity by three-quarters.

When light falls on a solar cell, it knocks electrons away from the cell’s material and leaves behind empty spaces called holes. Electrons and holes then flow in opposite directions and the result is an electric current.

 

The more electrons and holes there are, and the faster they flow, the bigger the current will be. Electrons, however, often get captured by holes while still inside the cell, and cannot therefore contribute to the current. The average distance an electron travels in a material before it gets captured is known as that material’s diffusion length. The larger the diffusion length, the more efficient the cell.

The silicon used in commercial solar cells has a diffusion length of ten nanometres (billionth of a metre), which is not much. Partly for this reason a silicon cell’s efficiency at converting incident light into electricity is less than 10%. Dr Snaith’s perovskite does better. It has a diffusion length of 1,000 nanometres, giving it an efficiency of 15%. And this, Dr Snaith says, has been achieved without much tweaking of the material. The implication is that it could be made more efficient still.

Perovskites are substances composed of what are known as cubo-octahedral crystals—in other words, cubes with the corners cut off. They thus have six octagonal faces and eight triangular ones. Perovskite itself is a natually occuring mineral, calcium titanium oxide, but lots of other elemental combinations adopt the same shape, and tinkering with the mix changes the frequency of the light the crystal absorbs best.

Dr Snaith’s perovskite is a particularly sophisticated one. It has an organic part, made of carbon, hydrogen and nitrogen, and an inorganic part, made of lead, iodine and chlorine. The organic part acts as a dye, absorbing lots of sunlight. The inorganic part helps conduct the electrons thus released.

It is also cheap to make. Purifying silicon requires high (and therefore costly) temperatures. Dr Snaith’s perovskite can be blended at room temperature. Laboratory versions of cells made from it cost about 40 cents per watt (ie, about half the cost of commercial silicon-based solar cells). At an industrial scale, Dr Snaith expects, that will halve again.

There are caveats, of course. The new perovskite is such a recent invention that its durability has not been properly tested. Many otherwise-promising materials fail to survive constant exposure to the sun, a sine qua non of being a solar cell. And the process of converting a laboratory-made cell into a mass-manufactured one is not always straight forward.

If it leaps these hurdles, though, Dr Snaith’s material will be a strong challenger for silicon. As solar power-generation becomes a mainstream technology over the next few years, the once-strange word “perovskite” may enter everyday language.

Reactor for Bulk Manufacturing of Core-Shell Quantum Dot Nanoparticles

Enables Large-Scale Production of Precision Quantum Dots for Medical Imaging, LEDs and Solar Cells

This multi-variable reactor facilitates the manufacturing of high-precision, core-shell quantum dots – nanoparticles made from semiconductive materials that display unique optical and electrical properties. Quantum dots have applications in computing, photovoltaic devices (solar panels), light emitting diodes (LEDs) and medical imaging equipment.

 

By modifying or “tuning” the precise size and quality of quantum dots, scientists can control the wavelength (bandgap) of light emitted by LEDs, and can select the properties for various other applications, such as fluorescence-based diagnostics and cell staining in medical imaging. Quantum dots are currently manufactured using batch methods, which under hydrothermal conditions, are time-consuming and subject to batch-to-batch variation in the desired properties. Detailed tuning of quantum dots to precise optical properties can be difficult using existing technology. Researchers at the University of Florida have developed a hydrothermal reactor that offers high-precision tuning of quantum dots for bulk production. The reactor enhances reliability, precision, uniformity and throughput during large-scale quantum dot manufacturing, and could help capture a significant portion of the global quantum dots market, which is expected to reach $670 million by 2015.

 

To Read More Go To The Link Here:

http://technologylicensing.research.ufl.edu/technologies/14105/reactor-for-bulk-manufacturing-of-core-shell-quantum-dot-nanoparticles

 

New theranostic nanoparticle delivers, tracks cancer drugs

(Nanowerk News) University of New South Wales (UNSW)  chemical engineers have synthesised a new iron oxide nanoparticle that delivers  cancer drugs to cells while simultaneously monitoring the drug release in real  time.

The result, published online in the journal ACS Nano (“Using Fluorescence Lifetime Imaging Microscopy to  Monitor Theranostic Nanoparticle Uptake and Intracellular Doxorubicin  Release”), represents an important development for the emerging field of  theranostics – a term that refers to nanoparticles that can treat and diagnose  disease.

“Iron oxide nanoparticles that can track drug delivery will  provide the possibility to adapt treatments for individual patients,” says  Associate Professor Cyrille Boyer from the UNSW School of Chemical Engineering.

By understanding how the cancer drug is released and its effect  on the cells and surrounding tissue, doctors can adjust doses to achieve the  best result.

Importantly, Boyer and his team demonstrated for the first time  the use of a technique called fluorescence lifetime imaging to monitor the drug  release inside a line of lung cancer cells.

“Usually, the drug release is determined using model experiments  on the lab bench, but not in the cells,” says Boyer. “This is significant as it  allows us to determine the kinetic movement of drug release in a true biological  environment.”

Magnetic iron oxide nanoparticles have been studied widely  because of their applications as contrast agents in magnetic resonance imaging,  or MRI. Several recent studies have explored the possibility of equipping these  contrast agents with drugs.

However, there are limited studies describing how to load  chemotherapy drugs onto the surface of magnetic iron oxide nanoparticles, and no  studies that have effectively proven that these drugs can be delivered inside  the cell. This has only been inferred.

With this latest study, the UNSW researchers engineered a new  way of loading the drugs onto the nanoparticle’s polymer surface, and  demonstrated for the first time that the particles are delivering their drug  inside the cells.

“This is very important because it shows that bench chemistry is  working inside the cells,” says Boyer. “The next step in the research is to move  to in-vivo applications.”

Source: University of New South Wales

Read more: http://www.nanowerk.com/news2/newsid=32972.php#ixzz2j9WI0HAR

Neutrons, electrons and theory reveal secrets of natural gas reserves

OAK RIDGE, Tenn., Oct. 28, 2013 – Gas and oil deposits in shale have no place to hide from an Oak Ridge National Laboratory technique that provides an inside look at pores and reveals structural information potentially vital to the nation’s energy needs.

The research by scientists at the Department of Energy laboratory could clear the path to the more efficient extraction of gas and oil from shale, environmentally benign and efficient energy production from coal and perhaps viable carbon dioxide sequestration technologies, according to Yuri Melnichenko, an instrument scientist at ORNL’s High Flux Isotope Reactor.

Scanning electron microscope image illustrating mineralogy and texture of unconventional gas reservoir. Note that nanoporosity is not resolvable with this image. SANS and USANS analysis is required to quantify pore size distribution and interconnectivity.          (hi-res image)

Melnichenko’s broader work was emboldened by a collaboration with James Morris and Nidia Gallego, lead authors of a paper recently published in Journal of Materials Chemistry A and members of ORNL’s Materials Science and Technology Division.

Researchers were able to describe a small-angle neutron scattering technique that, combined with electron microscopy and theory, can be used to examine the function of pore sizes.

Using their technique at the General Purpose SANS instrument at the High Flux Isotope Reactor, scientists showed there is significantly higher local structural order than previously believed in nanoporous carbons. This is important because it allows scientists to develop modeling methods based on local structure of carbon atoms. Researchers also probed distribution of adsorbed gas molecules at unprecedented smaller length scales, allowing them to devise models of the pores.

“We have recently developed efficient approaches to predict the effect of pore size on adsorption,” Morris said. “However, these predictions need verification – and the recent small-angle neutron experiments are ideal for this. The experiments also beg for further calculations, so there is much to be done.”

While traditional methods provide general information about adsorption averaged over an entire sample, they do not provide insight into how pores of different sizes contribute to the total adsorption capacity of a material. Unlike absorption, a process involving the uptake of a gas or liquid in some bulk porous material, adsorption involves the adhesion of atoms, ions or molecules to a surface.

This research, in conjunction with previous work, allows scientists to analyze two-dimensional images to understand how local structures can affect the accessibility of shale pores to natural gas.

“Combined with atomic-level calculations, we demonstrated that local defects in the porous structure observed by microscopy provide stronger gas binding and facilitate its condensation into liquid in pores of optimal sub-nanometer size,” Melnichenko said. “Our method provides a reliable tool for probing properties of sub- and super-critical fluids in natural and engineered porous materials with different structural properties.

“This is a crucial step toward predicting and designing materials with enhanced gas adsorption properties.”

Together, the application of neutron scattering, electron microscopy and theory can lead to new design concepts for building novel nanoporous materials with properties tailored for the environment and energy storage-related technologies. These include capture and sequestration of man-made greenhouse gases, hydrogen storage, membrane gas separation, environmental remediation and catalysis.

Other authors of the paper, titled “Modern approaches to studying gas adsorption in nanoporous carbons,” are Cristian Contescu, Matthew Chisholm, Valentino Cooper, Lilin He, Yungok Ihm, Eugene Mamontov, Raina Olsen, Stephen Pennycook, Matthew Stone and Hongxin Zhang. The research, funded by DOE’s Office of Basic Energy Sciences, utilized the following DOE Office of Science user facilities:

ORNL’s Spallation Neutron Source (http://neutrons.ornl.gov/faciliities/SNS/) is a one-of-a-kind research facility that provides the most intense pulsed neutron beams in the world for scientific research and industrial development.

HFIR (http://neutrons.ornl.gov/facilities/HFIR/) at ORNL is a light-water cooled and moderated reactor that is the United States’ highest flux reactor-based neutron source.

The ShaRE User Facility (http://web.ornl.gov/sci/share/) makes available state-of-the-art electron beam microcharacterization facilities for collaboration with researchers from universities, industry and other government laboratories.

As a national resource to enable scientific advances to support the missions of DOE’s Office of Science, the National Energy Research Scientific Computing Center (http://www.nersc.gov), annually serves approximately 3,000 scientists throughout the United States.

UT-Battelle manages ORNL for the Department of Energy’s Office of Science. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of the time. For more information, please visit science.energy.gov.

Automated and scalable inline two-stage synthesis process for high quality colloidal quantum dots

By Michael Berger. Copyright © Nanowerk

(Nanowerk Spotlight) Colloidal quantum dot (CQD)  nanocrystals are attractive materials for optoelectronics, sensing devices and  third generation photovoltaics, due to their low cost, tunable bandgap – i.e.  their optical absorption can be controlled by changing the size of the CQD  nanocrystal – and solution processability. This makes them attractive candidate  materials for cheap and scalable roll-to-roll printable device fabrication  technologies.

 

One key impediment that currently prevents CQDs from fulfilling  their tremendous promise is that all reports of high efficiency devices were  from CQDs synthesized using manual batch synthesis methods (in classical  reaction flasks).

 

Researchers have known that chemically producing nanocrystals  of controlled and narrow size-distributions requires stringent control over the  reaction conditions – e.g. temperature and reactant concentration – which is  only practical for small-scale reactions.

 

Such a synthesis is extremely  difficult to scale up, hence very costly to mass produce without severely  compromising quality.   The reason for this is that, just like rain droplets,  nanocrystals form sequentially by ‘nucleation’ and ‘growth’. Both these  phenomena are highly sensitive to temperature and reagent concentration.  Moreover, nucleation and growth must occur at substantially different  temperatures and, in fact, to obtain nanocrystals of uniform sizes, one must be  able to rapidly cool down the reaction from the nucleation temperature to the  growth temperature.

 

Hence, the quality of the product is contingent upon how  well and fast one can homogenize the reactor, both chemically and thermally.   Unfortunately, the only way to scale up batch reactors is by  increasing their volume, whereupon it becomes difficult to homogenize the  reactor and impractical to rapidly cool. The end result is nanocrystals of  low-quality and broad size distributions, which are not useful for fabricating  devices.

Some researchers have sought to circumvent this limitation by  conducting the reactions in narrow fluidic channels (less than a 1 mm in  diameter) while the reactants are continuously pumped through the channels, so  called ‘continuous-flow reactors’.

 

Conceptually, this scheme has several advantages. Narrow-width  channels afford uniform heating and mixing of the reaction, while the reaction  is scalable by simply increasing channel length and pump rate of the reagents.  This sort of scaling does not effect the quality of the product, because the  channel width, and hence the effective reaction volume, remains the same.  Despite these advantages, most attempts to use continuous-flow reactors in the  past have resulted in nanocrystals with a much lower quality than the batch  produced ones.

 

“We have analyzed the nucleation and growth of CQDs in  continuous-flow reactors and realized that, in order to achieve controllable  size and narrow size-distributions, one must employ two temperature stages in  the reactor: one for nucleation, and another for growth,” Osman Bakr, an  assistant professor in the Solar & Photovoltaics Engineering Research Center at King  Abdullah University of Science and Technology (KAUST), tells Nanowerk.

“By  separating these two crucial steps in the formation of the CQDs in time,  temperature, and space, we were able to obtain very high quality nanocrystals,  as good as the best batch synthesis, by a process that is low-cost,  mass-producible, and automated.”

 

 

Schematic of (a) a conventional batch synthesis setup and (b) a  dual-stage continuous flow reactor setup with precursor A (Pb-oleate,  octadecene) and precursor B (bis(trimethylsilyl) sulfide in octadecene).  (Reprinted with permission from American Chemical Society)

 

Reporting their findings in ACS Nano (“Automated Synthesis of Photovoltaic-Quality Colloidal Quantum  Dots Using Separate Nucleation and Growth Stages”), Bakr and his team  demonstrated the quality of the CQDs produced by their method by using them to  make CQD-based solar cells that showed very high efficiencies.

 

“In this paper, we developed an automated, scalable, in-line  synthesis methodology of high-quality CQDs based on a flow-reactor with two  temperature-stages of narrow channel coils,” says Professor Ted Sargent from the  University of Toronto who, together with Bakr, led this work. “The flow-reactor  methodology not only enables easy scalability and cheap production, but also  affords rapid screening of parameters, automation, and low reagent consumption  during optimization. 

Moreover, the CQDs are as good in quality and device  performance as the best CQDs that are produced in the traditional batch  methodology.”   The team also developed a general theory for how one can use the  flow-reactors to finely tune the quality and size distribution of the CQDs, and  explained why previous attempts of using flow-reactors based on a  single-temperature-stage, as opposed to a dual-temperature-stage, necessarily  produce CQDs of low-quality and broad size distribution.

 

This work paves the way towards the large-scale and affordable  synthesis of high-quality CQD nanocrystals in tunable sizes, enabling  photovoltaics, light-emitting diodes, photodetectors, and biological tagging  technologies that take advantage of the nanoscale properties of those promising  materials.

 

“Over the last ten years we have seen tremendous advancements in  software and computer integration, in items that we use in our everyday lives,”  says Bakr. “Flow-reactors as a platform are ideally placed to take advantage of  this trend. Software that automates the routines of flow-reactors already  exists. In the near future, researchers will be able to run and monitor hundreds  of experiments to produce CQDs from home using a mobile app.

 

Moreover, because  flow-reactors contain very few moving parts, essentially just programmable  pumps, I expect that it will become an automated research platform that most  labs studying nanocrystals can afford.”   “Our work has shown that flow-reactors can produce nanocrystals  that are as good as the best batch produced reactions, with exquisite control  over reaction conditions,” he adds. “We believe that this will encourage the  nanomaterials community to take advantage of the enormous productivity gains in  R&D afforded by flow-reactors, which other chemical industries, such as  pharmaceuticals, are currently utilizing earnestly.”

Read more: http://www.nanowerk.com/spotlight/spotid=32945.php#ixzz2j2YbZvu8

Inkjet Print Process Devised for Quantum Dot Organic LEDs

 

 

  *** Original Post by Alan Kotok from “Science and Enterprise. ***

Engineers at University of Louisville in Kentucky developed a process for making organic light-emitting diodes (OLEDs) with quantum dots and applied with inkjet printing, a common manufacturing technology. The findings of the research team led by Louisville engineering professor Delaina Amos will be presented next week at the Optical Society’s Conference on Lasers and Electro-Optics in San Jose, California.

OLEDs are solid-state devices made with thin films of organic molecules that generate light when an electric current passes through. Displays made with OLEDs can be made much thinner and flexible, and use less power than LED or liquid-crystal displays found in conventional flat-screen televisions or computer monitors. However, widespread manufacturing of OLEDs has been held back because of the cost of materials and their expensive production processes.

The Louisville team aims to create an OLED manufacturing technique with inkjet printing, an established manufacturing process widely used in commercial settings. Their methods use quantum dots made of cadmium selenide, an inorganic material, forming a hybrid type of OLED. Quantum dots are nanoscale semiconductor crystals, which have among other properties photoelectric effects.

These synthesized quantum-dot OLEDs, says Amos, are more efficient than earlier OLEDs and can present a wider spectrum of colors. She adds that they are also less expensive to produce and more environmentally friendly, using low-toxicity materials.

Amos and colleagues demonstrated their technology using cadmium selenide quantum dots in a solution applied with an inkjet printer. The OLEDs are applied in layers, with interfaces between the layers designed to improve the efficiency with which electrons are transferred through the device.

The demonstrations so far created small-scale (1-inch by 1-inch square) OLED devices, but Amos says they can be scaled up to 6 by 6 inches or larger within the next few months. “Ultimately,” notes Amos, “we want to have low cost, low toxicity, and the ability to make flexible devices.”

Read more:

• Merck, Seiko Epson to Partner on Organic LED Inkjet Inks
• Project to Study Light-Enabled Quantum Dot Circuits
• New Quantum Dot Material Boosts Solar Cell Efficiency
• Nanotech Solar Energy Paint Developed
• Manufacturing Process Devised for More Economical LEDs

ONE Box Girl Scout Cookies = $15 Billion (Converting Carbon Sources to Graphene)

Rice University lab shows troop how any carbon source can become valuable graphene.
Scientists can make graphene out of just about anything with carbon — even Girl Scout cookies.

Graduate students in the Rice University lab of chemist James Tour proved it when they invited a troop of Houston Girl Scouts to their lab to show them how it’s done.

 

*** WOW! Team GNT KNEW we should have bought more Girl Scout Cookies in this year’s annual ‘cookie drive’!  – Cheers!

Understanding the ultimate limit of quantum dot linewidths

Colloidal quantum dots are potentially useful as artificial atoms for applications in emerging quantum technologies. However, previous measurements indicated that these nanocrystals are prone to significant decoherence (as they transition from quantum to classical behaviour). The origins behind this phenomenon remained a mystery, but researchers at the University of Bordeaux in France now provide a possible explanation. Thanks to a novel light absorption-based technique, which reveals that the decoherence is caused by spontaneous charge noise in the environment surrounding the nanocrystals, decoherence-limited linewidths of approximately one gigahertz have been found. The finding should aid in the design of quantum photonic structures containing nanocrystals.

Environmental charge noise determines the linewidth of quantum dots

In the quantum regime, particles can act like waves and interfere with each other. However, this quantum interference vanishes as we approach macroscopic length scales as the particles begin to interact with their environment. Physicists usually try to avoid this phenomenon, which is known as decoherence.

Colloidal quantum dots for their part are plagued by spectral instabilities, known as spectral diffusion, which are detrimental to their application in quantum technologies. Spectral diffusion comes about as the excited quantum dot shifts its emission frequency in response to slight changes in its local environment. The phenomenon is unfortunate since colloidal quantum dots could offer some unique advantages in this field thanks to their being compatible with a wide range of photonic structures and the fact that they can be accurately integrated within these structures. Understanding the origin of spectral diffusion is thus important and would ultimately help researchers mitigate these effects. 

A team has now studied the fast spectral diffusion process using a resonant photoluminescence excitation technique in which a narrow-band laser is scanned across an absorption line of a single quantum dot and the signal detected The shape of the measured spectral line can show whether the spectral diffusion is caused by the absorption of a photon or not, and the Bordeaux researchers have found that at the highest resolution the spectral diffusion process does not depend on photon absorption. 

In this work, the properties of charge noise in disordered media were used to demonstrate that a single colloidal quantum dot is capable of detecting spontaneous changes in the environmental charge distribution via the quantum confined Stark effect. Such fluctuations were found to be compatible with the gigahertz linewidths previously reported. Fast spectral diffusion in quantum dots can thus be attributed to spontaneous environmental charge noise within the disordered local environment, something that ultimately sets a limit on the linewidth that can be obtained with colloidal quantum dots.

More information can be found in the journal Nanotechnology (in press).

Further reading

Quantum dot blend gives wide-bandwidth FET-based photodetector (Jul 2012) Novel recombination layers improve multijunction photovoltaics (Jun 2012) How far can charge carriers travel in CQD films? (Jun 2013) Nanoparticles pinpoint brain activity (Jan 2006)

About the author

The research was conducted in the Nanophotonics Group at Bordeaux headed by Professor Brahim Lounis at the University of Bordeaux. Dr Mark Fernee is an invited researcher specializing in the photophysical properties of nanocrystals with a particular emphasis on applications in quantum technologies. Chiara Sinito is a PhD student in the group, who together with Dr Yann Louyer participated in the experiments. Professor Philippe Tamarat is an expert in single molecule and single nanoparticle detection.

Organic semiconductors open path for flexible electronics

News & Trends • Posted:16 October 2013

Scientists from the Emergent Molecular Function Research Group at the RIKEN Centre for Emergent Matter Science have developed a synthetic procedure that according to them makes it easier to tailor the chemical structure of an important organic semiconductor.

 

Organic semiconductors made from small aromatic molecules can be dissolved and screen-printed onto many substrates, including plastics, opening the path for ‘flexible’ electronic devices such as low-cost polymer solar cells.

Kazuo Takimiya and colleagues, in collaboration with researchers from Hiroshima University, have now developed a synthetic procedure that makes it easier to tailor the chemical structure of an important organic semiconductor.

Kazuo Takimiya and his team, in collaboration with researchers from Hiroshima University, were studying molecules known as diacene-fused thienothiophenes when they discovered their new synthetic procedure. Diacene-fused thienothiophenes are composed of interlocking benzene and sulphur-containing aromatic rings and are more durable, and have higher charge carrier mobilities, than most other organic semiconductors. Although current schemes to make these compounds are relatively straightforward, they are also difficult to modify. Thus, chemists have a hard time producing derivatives based on this ring system with more desirable properties.

The researchers devised a creative synthesis that, instead of relying on bulky aromatic precursors, generates diacene-fused thienothiophenes from small molecules through two consecutive ring-forming reactions. First, they generated an active reagent called phenylsulfenyl chloride that joins to a benzene–acetylene molecule and transforms it into a three ring system. Then, they used selective carbon–hydrogen bond activation to set off a rare intramolecular coupling that produces a molecule with four fused rings known as benzothieno-benzothiophene (BTBT). Takimiya explained that this approach produces excellent yields and makes it possible to scrutinise numerous BTBT derivatives by making simple changes to the starting reagents.

Trials revealed that this technique was particularly useful for extending the ring structure of BTBT-type molecules. For example, by substituting double- and triple-fused benzene molecules into the synthetic procedure, the team linearly constructed the BTBT substructure to form five, six and seven aromatic rings. Intriguingly, these new derivatives have an asymmetric structure that may dramatically improve their solubility—an important processing feature for printed electronics and one that is difficult to achieve using existing synthetic techniques.

Lengthening the BTBT framework to an eight-ringed symmetric structure also yielded a potent new organic semiconductor with excellent thermal stability and a charge carrier mobility five times higher than that of BTBT. “This mobility is among the highest recorded for thin film organic field-effect transistors, meaning that this molecule could be a candidate for real flexible electronics applications in the future,” stated Takimiya.