Switches are perhaps the most basic type of machine. A child could design, operate, and repair it. Two metal contacts touch which “makes” a circuit and the contacts then separate to break it. There’s a moving part that applies a force to the contacts called an actuator, or in most cases called a toggle. When the contacts touch there is no space between them which means electricity can flow from one to the other. When they’re separated by a space, no electricity can flow. Simple, effective, and the basis for any other electrical component. It would be hard to imagine a useful electronic device that didn’t have the capability to somehow disrupt or impede the flow of electricity when it was no longer needed.
Chemists are now beginning to look at circuity made from organic molecules. The reasons are simple. Sinking down to the molecular level is the key to increasing the computational density of our devices. We started out with vacuum tumbes, yes? Large, bulky, slow, and prone to overheating. ENIAC – the Electronic Numerical Integrator And Computer – was the first general purpose computer and its components filled up a large room, due mainly to the 17,000 vacuum tubes that were required. We shrunk down to individual transistors. This was a huge improvement and it revolutionized – quite literally – the computing industry. We could fit more processing components into a given amount of space, and so computers became more powerful. We then shrunk down to integrated circuits, which had thousands of transistors on a single chip. The same theory applied here. We could fit more units into a given amount of space and so the computers became more powerful.
Researchers are now on the brink of making the ultimate size reduction step: going from integrated circuits down to molecules. This will be the final step, as you can’t get any smaller than molecules without dissolving into a random assortment of atoms. Molecular circuitry – electronic components designed from conductive molecules – is the next boundary, and once we cross it, we will launch our already impressive computer devices into a new era. However, we first have to take that shaky initial step. We can’t build a circuit without having a switch. If we don’t have a controllable method of interrupting electricity flow (the ON/OFF which is so vital to computing), then we’re never going to get anywhere. What we need is a molecular switch, something which conducts electricity and is on the molecular scale.
Scientists at Columbia University report that they have now taken this step. Their switch allows electricity to flow when it’s “closed” and breaks the flow of electricity when it’s “open”. The chemists who worked on the project describe their invention in the Journal of the American Chemical Society. Conductive carbon nanotubes serve as the actual molecular wires, and the switch consists of a phenylene vinylene with pyrrole units in the chain. In one oxidation state, the pyrroles are kinked with respect to each other, and so their molecular orbitals are not aligned; electricity cannot flow without this conjugation, and so the switch is open. In the other oxidation state the pyrroles lie flat in the same plane and so their molecular orbitals are aligned. The switch is closed, and electricity can flow. This oxidation state can be controlled by irradiation with the correct light frequency.
This technology is simple, the switch is fully reversible, and the circuitry is durable. This technique accomplishes the most simple of molecular circuitry components – the switch – and it does so with the minimum of fuss. I’m sure that this molecule will become a staple for organic chemists.
The source of this article can be found at: http://pubs.acs.org/doi/abs/10.1021/ja073127y