(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.
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.
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 Logic Devices” in a
recent issue of the Journal of the American Chemical Society.
previous examples of molecular logic systems have been able to carry
out one, or a few different logic operations, this molecule can be
reconfigured to perform 13 simply by changing the input or output
wavelengths,” Gust told PhysOrg.com. “In addition, it uses light for all inputs and outputs, which avoids
some of the problems encountered when using chemicals as inputs.”
general, chromophores 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.
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
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.
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.”
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.
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.
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 wavelengths of light and to influence each other’s properties.
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
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.
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.”
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.
the future, the researchers plan to address some of the biggest
challenges facing molecular logic, such as the efficient wiring
(concatenation) of logic switches.
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 molecules.”
SOURCE: American Chemical Society