Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Light driving light: how an optical transistor operates

11.10.2011
The transistor is one of the most influential inventions of the 20th century.

Its crucial function is to drive electrical signals utilising electrical signals in television sets, telephones, PCs and other devices. The smaller the circuits with which the signals are conducted, the faster the data processing.

At the University of Bayreuth, a research team centred around Prof. Dr. Jürgen Köhler, Dr. Martti Pärs and Prof. Dr. Mukundan Thelakkat has now demonstrated the amplifying function of an optical transistor. The point: in this transistor, light substitutes electricity. Light signals are driven by light signals.

In the recent online edition of the journal "Angewandte Chemie International Edition", the Bayreuth scientists introduce their discovery. Dr. Martti Pärs, a young physicist, made a particularly noteworthy contribution to the research. The results that have now been published evolved from the close co-operation between Experimental Physics and Macromolecular Chemistry within the Bayreuth campus. The results are the foundation of a completely new generation of transistors. The DFG supports the research in this area within the framework of the research training group "Photophysics of synthetic and biological multichromophor systems".

Two molecules in the team:
one light-driven switch and a strongly illuminating partner
The conceptual model of an optical transistor used in Bayreuth is simple. Two molecules are chemically bound. Using light signals with varying wavelengths, one of the two molecules is alternately brought into a state A or B. The molecule thereby reacts like a switch, alternating between two contrasting states. Depending on whether this light-driven molecular switch is in state A or B, the molecule bound to it emits a weak or strong light signal: light driving light. During this process, a considerable amplification effect evolves as a small light signal is sufficient to bring the molecular switch into a condition whereby the partner molecule strongly fluoresces.
Principal benefits:
highest efficiency within a tiny space
A transistor functioning as described above provides considerable benefits compared to conventional transistors: the latter cannot be optionally reduced in size due to physical reasons. All endeavours to develop the smallest possible circuit for the transport of electrical signals are naturally constrained. However the driving of light signals utilising light signals can be realised at a molecular level as the Bayreuth scientists have now demonstrated. In theory, optical transistors may already exist at the molecular scale. They are innately smaller and therefore faster than electrical transistors.

Another benefit: several optical "mini transistors" can be assembled to become a larger and even more powerful transistor because light signals, as opposed to electrical signals, do not interfere with each other. Therefore a multitude of data is processed simultaneously within a tiny space. Finally, any optical transistor regardless of size is superior relating to one aspect: all signals are processed at the speed of light – to be faster is not possible.

Physical details:
the interior of an optical transistor
The switch molecule used in Bayreuth is dithienylcyclopentene (DCP). In the centre of the symmetrical molecule is a carbon ring. The closed ring is opened as soon as it is hit by an ultra-violet ray of light (280 - 310 nm). The open ring is closed as soon as it is exposed to a visible coloured ray of light (500 - 650 nm). DCP is termed in research a photochrome / photoswitch molecule because it alternates, depending upon the light ray’s wavelength, between the two structures.

At the opposite ends of the DCP molecules, the Bayreuth researchers have attached two organic chromophores, belonging to the perylene bisimides (PBI) group. PBI molecules are known for their ability to fluoresce strongly. This is always the case when a PBI molecule absorbs light energy and emits it.

A PBI molecule that is attached like an arm to a DCP molecule fluoresces with varying intensity – depending on whether the ring in the molecular switch is open or closed. When it is closed, the DCP is at a relatively low energy level. Therefore the PBI transfers the greatest part of its absorbed light energy to the DCP. The DCP dissipates light energy without fluorescence. In this case, the PBI weakly fluoresces. However, when the ring in the DCP is open, we observe the opposite. The DCP is at such a high energy level that the PBI is unable to pass on light energy to the DCP. Instead, it fully emits the absorbed light energy. The PBI is strongly fluorescent.

Further research challenges

Based on the above research results, a future vision of a new generation of transistors has emerged. For this vision to be realised one day, further research is necessary. For instance, it seems as if the fluorescent PBI molecules fade during longer periods of time. Consequently, their illumination power weakens. It is worthwhile to examine this effect more closely. A further observation of test conditions used so far is that it takes a relatively long period of time for the rings to open and close for a large number of DCP molecules. As a result, the gaps between the light signals driven by this process are rather large. The Bayreuth research team is therefore striving for a solution in order to minimise these periods of time.

Publication:

Martti Pärs, Christiane C. Hofmann, Katja Willinger, Peter Bauer,
Mukundan Thelakkat, and Jürgen Köhler,
An Organic Optical Transistor Operated under Ambient Conditions,
in: Angewandte Chemie International Edition 2011, 50,
Article first published online: 5 Oct 2011
DOI-Bookmark: 10.1002/anie.201104193
Contact for further information:
Prof. Dr. Jürgen Köhler
Experimental Physics IV
University of Bayreuth
95440 Bayreuth, Germany
Telephone: +49 (0)921 / 55-4000 and 55-4001
Email: Juergen.Koehler@uni-bayreuth.de
Dr. Martti Pärs
Experimental Physics IV
University of Bayreuth
95440 Bayreuth, Germany
Telephone: +49 (0)921 / 55-4003
Email: Martti.Paers@uni-bayreuth.de
Prof. Dr. Mukundan Thelakkat
Applied Functional Polymers
University of Bayreuth
95440 Bayreuth, Germany
Telephone: +49 (0)921 / 55-3108
Email: Mukundan.Thelakkat@uni-bayreuth.de

Christian Wißler | Universität Bayreuth
Further information:
http://www.uni-bayreuth.de

More articles from Physics and Astronomy:

nachricht DGIST develops 20 times faster biosensor
24.04.2017 | DGIST (Daegu Gyeongbuk Institute of Science and Technology)

nachricht New quantum liquid crystals may play role in future of computers
21.04.2017 | California Institute of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

DGIST develops 20 times faster biosensor

24.04.2017 | Physics and Astronomy

Nanoimprinted hyperlens array: Paving the way for practical super-resolution imaging

24.04.2017 | Materials Sciences

Atomic-level motion may drive bacteria's ability to evade immune system defenses

24.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>