Single molecule performs multiple logic operations simultaneously

May 23, 2011 by Lisa Zyga feature
(Left) The structure of the FG-DTE molecule, which is made of three photochromes that can switch between two different states when irradiated with light of different wavelengths. (Right) A checklist of some of the features of the all-photonic molecular logic device. Image credit: Joakim Andréasson, et al. ©2011 American Chemical Society.

( -- While molecules have already been used to perform individual logic operations, scientists have now shown that a single molecule can perform 13 logic operations, some of them in parallel. The molecule, which consists of three chromophores, is operated by different wavelengths of light. The scientists predict that this system, with its unprecedented level of complexity, could serve as a building block of molecular computing, in which molecules rather than electrons are used for processing and manipulating information.

The scientists and engineers, Joakim Andréasson from Chalmers University of Technology in Göteborg, Sweden; Uwe Pischel from the University of Huelva, Spain; and Stephen D. Straight, Thomas A. Moore, Ana L. Moore, and Devens Gust from Arizona State University, have published their study called “All-Photonic Multifunctional Molecular ” in a recent issue of the Journal of the American Chemical Society.

“While previous examples of molecular logic systems have been able to carry out one, or a few different , this molecule can be reconfigured to perform 13 simply by changing the input or output wavelengths,” Gust told “In addition, it uses light for all inputs and outputs, which avoids some of the problems encountered when using chemicals as inputs.”

In general, are the parts of a molecule that absorb light of specific wavelengths while transmitting other wavelengths, and are responsible for the molecule’s color. When chromophores can be switched between two different states by being irradiated with light of different wavelengths, they have the ability to perform binary logic operations and effectively serve as transistors. These photoswitchable, bistable chromophores are called photochromes.

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Here, the researchers used three photochromes – one dithienylethene (DTE) and two fulgmides (FG) – to build a light-responsive molecule. Each of these photochromes can exist in either an open or closed isomeric form, and can be switched back and forth between forms with light pulses of different wavelengths.

The two forms that each photochrome can take represent the two states that serve as the basis for performing binary logic operations. Various combinations of the three photochromes in different isomeric forms can be used to perform binary arithmetic, such as addition and subtraction. Although previous molecular-based systems have performed binary arithmetic, the FG-DTE molecule is the first that can perform these operations using only two inputs: light with wavelengths of 302 nm and 397 nm. Also, all three photochromes can be reset by green light irradiation (460-590 nm). These features allow the molecule to perform addition and subtraction in parallel, simply by having light convert the photochromes to different isomeric forms.

“All of these 13 logic operations share the same initial state, that is, the molecule is always ‘reset’ to one and the same state by the use of green light, irrespective of which logic function is to be performed,” said Andréasson. “This is another unique feature of our molecule.”

The researchers also demonstrated that the FG-DTE molecule can perform non-arithmetic functions. For example, as a digital multiplexer, the molecule can act as a mimic of a mechanical rotary switch to connect any one of several inputs to an output. As a demultiplexer, the molecule can separate two signals that have been multiplexed into one output.

Further, the FG-DTE molecule can perform sequential logic functions, in which inputs must be applied in the correct order, such as for a keypad lock. The molecule can also operate as a transfer gate by transferring the state of an input to that of an output, which is useful for complicated computational operations. The researchers also demonstrated that the molecule can act as an encoder and decoder, by compressing digital information for transmission or storage, and then recovering the information in its original form.

While each of these individual logic operations has previously been performed by molecular systems, the FG-DTE molecule is the first to unite them all in a single molecular platform. Transistors and other more traditional logic devices do not have the same functional flexibility, which the researchers attribute to the chromophores’ ability to respond differently to different and to influence each other’s properties.

As for applications, the researchers note that it’s unlikely that such molecular devices will soon replace electronic computers, but they could have applications in nanotechnology and biomedicine, such as for data storage, labeling and tracking micro-objects, and programmed drug release.

“In the near term, molecular logic devices will complement, rather than compete with, electronic devices,” Gust said. “In principle, molecular computing could be implemented with extremely small switch sizes, since the operational units are molecules. Photonically operated molecular devices such as the one we describe can also be easily reconfigured to perform a variety of different logic functions, can operate at high speeds, and can be arrayed in three dimensions, rather than the planar arrangements usually found in electronics.

“Molecular logic devices can be employed where electronic ones cannot,” he added. “For example, they can be used to label and track nanoparticles and nanoscale components of biological organisms. On the other hand, most photochromes currently are not sufficiently stable to stand up to the large number of cycles required for useful full-scale computing. In addition, complex computing will require convenient ways for nanoscale logic devices to communicate with one another.”

“In addition, the application of molecular logic in biological systems, such as the human body, is still relatively unexplored, although molecular systems are better suited for this purpose compared to electronic devices,” said Andréasson.

In the future, the researchers plan to address some of the biggest challenges facing molecular logic, such as the efficient wiring (concatenation) of logic switches.

“One of the major challenges of molecular logic is concatenation of logic operations,” Gust said. “In electronics, this can be done simply by wiring the output of one element to the input of the next. We need to find ways of achieving similar results in .”

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More information: Joakim Andréasson, et al. “All-Photonic Multifunctional Molecular Logic Devices.” Journal of the American Chemical Society. DOI:10.1021/ja203456h

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3 / 5 (2) May 23, 2011
This is incredible, and is quite a different animal from the DNA chemical computer.

To me, there is still some things this article leaves in question.

How stable is the molecule?

Is the "memory" volatile or non-volatile?

How much "overhead" is there in terms of the size of the photonic devices used to set and detect the molecule's state?

Would it even be "worth it" compared to the best electronic circuits allowed by the laws of physics?

It seems to me that to be generally useful, you need to be able to have a system of circuitry in which these molecules have self-sustained communicatin with one another, which is to say, atomically precise lattice and molecular logic circuitry composed entirely of this molecule and/or other similar molecules according to unique molecular function.
1 / 5 (2) May 23, 2011
Based on the diagram, this molecule is at most 16 atomic radii long and 20 atomic radii wide, using the carbon atoms and hexagon structures as a metric. though these arms are probably "curled" into the third dimension in the real world.

The radius of a carbon atom is 77.2 picometers, or 0.772 nanometers.

This means the molecule is no more than 15.44nm wide by 12.35nm long, even if treated as a planar object.

So over all, in area it would be significantly less than the 14nm process electronic transistors Intel will be making in a few years, and regardless of how little or how much the arms of the molecule are curled up, it will be vastly smaller in total volume than an Intel 14nm process transistor.
not rated yet May 23, 2011
i LIKE it! The linking aspect seems doable if you do photochrome -> electronic gate -> photochrome (as they suggest in the article).
Long-term stability is another consideration - it seems to me that the molecule will decay over time, as the angle of the outgoing photon is not fixed and therefore will involve energy loss in any real-world circuit.
Very cool!
not rated yet May 24, 2011
This require light with different wavelengths.

Now, how do you change wavelengths? What circuitry and/or mechanics is required to accomplish that? At the end, what did we gain - in terms of *real* switching speed and power savings?
not rated yet May 25, 2011
This require light with different wavelengths.

Now, how do you change wavelengths? What circuitry and/or mechanics is required to accomplish that? At the end, what did we gain - in terms of *real* switching speed and power savings?

Photons are among the least "massive" particles in the universe. In fact, they have no rest mass. This means it costs no energy for "moving" a photon.

In an electronic computer the electricity itself costs you energy,usually expressed as heat waste, and most of the electricity isn't actually doing calculations, it is maintaining a current to maintain the non-volatile memory.

In an ordinary molecular computer, such as a DNA computer, calculations are done in arrangement of base pairs, or more precisely, the ionic charge on molecules. Thus, you must "pay" the energy cost to re-orient molecules, which costs more than moving individual electrons, but the advantage is that the "memory" is "quantum" and electrically non-volatile.
not rated yet May 25, 2011
Now by "quantum" I do not mean in the sense of a "Quantum computer" which uses entanglement. What I am referrnig to is that a DNA computer theoretically uses exactly "one electron plus the energy cost of moving a molecule" per "bit operation," and then costs no energy until a new operation is done, no matter how long the bit must be maintained.

In an electronic computer, making and maintaining a "1" in a bit costs energy proportional to the time it is maintained, since the current must always stay on, consuming more power. However, electronic computers "should" be faster than DNA computers, because you are only moving the mass of an electron, instead of the mass of an entire molecule.

So you can see how a PHOTONIC molecular computer would be BETTER in both respects than either a DNA computer or an electronic computer, because photons are less massive than electrons, an because you have the same "quantum" and non-volatile advantages of a DNA computer, but not the mass drawback.
not rated yet May 25, 2011
So for example, a PHOTONIC molecular computer in principle stors "bits" in the electron orbital, the same as a DNA molecular computer does.

The key difference is the DNA computer stores through chemical bonds, but the photonic computer would store a "Bit" in the form of a captured photon stored in an electron by increasing its orbital energy. So for some operations, a photonic computer could theoretically use as little as one photon per bit operation.

Even if this goal is never acheived, if real photonic computers could be made within an order of magnitude of the quantum limit, I should think it would make anything we have today look like cave man technology in terms of capabilities.
not rated yet May 25, 2011
though these arms are probably "curled" into the third dimension in the real world.

Aromatic rings (the hexagon structures you're referring to) are planar. Since each arm is a series of aromatic rings, each arm would not have any curve to it. The only opportunity I see for rotation in the state shown above is at the -C-C-N bonds for the FG groups off of the central aromatic ring.

The excited states likely have more curved arms though as certain double bonds become single bonds on exposure to certain light wavelengths which allow for rotation in the molecule.
not rated yet May 25, 2011
Based on the diagram, this molecule is at most 16 atomic radii long and 20 atomic radii wide, using the carbon atoms and hexagon structures as a metric.

I would recommend looking up the information on aromatic bond lengths, and carbon-carbon single, double, and triple bond lengths to get a better idea of the length of the molecule rather than using atomic radii.

Also, the fluorines, oxygens, and nitrogens will have a significant effect on bond length as their electronegativity pull electrons away from the carbon atoms shortening the C-C bonds adjacent to them and will have a lesser effect on C-C bonds one or two carbons away.