Get excited: Exploring the computing potential of high-energy states in perylene

Australian researchers have taken the first steps to creating ultrafast computing devices smaller than a nanometre by studying the behaviour of perylene as a candidate molecule for excitonic logic operations.

Conventional computing devices are currently made from semiconducting electronic chips and function through binary logic, where high or low voltages are used to encode information in ‘bits’ of 1 or 0.

In a proposed alternative, information would instead be encoded in quasi-particles known as excitons, formed when a material becomes electronically excited. Excitonic circuit components could be constructed using single molecules, allowing them to be significantly smaller than contemporary transistors and diodes, perhaps even smaller than a nanometre. To put that in perspective, a sheet of paper is around 100,000 nanometres thick.

Excitonic processes occur on extraordinarily fast timescales, from femtoseconds (one quadrillionth of a second) onwards. Conducting information processing operations with excitons could help to build devices that operate much faster than modern computers.

One possible method for using excitons in information processing involves performing fundamental computer operations (known as “logical operations”) with different excited states within the same molecule.

By changing the excitation conditions of the material, such as the colour of light used for excitation, excitons can be formed in different states. Measuring these exciton states through techniques such as fluorescence spectroscopy or spin resonance could then give the outputs of these logical operations.

However, to make this proposal a reality, researchers must identify molecular systems which are able to remain in highly-excited states for long enough to be of practical use.

Among the candidate molecules is the hydrocarbon perylene. While some of perylene’s photophysical properties offer promise for hosting excitonic logical operations, its high-lying excited states remain relatively unexamined. 

Exciton Science researchers based at the University of Melbourne, RMIT University and UNSW Sydney combined femtosecond spectroscopy with quantum chemical calculations to better understand perylene’s excited-state behaviour.

Dr Rohan Hudson, a Research Fellow at the University of Melbourne and the first author of the paper, said: “The key result that we discovered is that there are two high-lying excited states in perylene we can access fairly readily.

“For both of these states, we’ve quantified how long they take to relax back down to a low-lying excited state. These lifetimes are short – on the order of hundreds of femtoseconds – but this might be just long enough to harness these high-energy excitations for performing logical operations .”

Rohan and his colleagues will now seek to expand on the encouraging initial findings with a long-term view toward real-world applications.

“The plan is to take these results that we found in solution-phase perylene and apply that knowledge to some sort of solid sample, to try and use two-photon or two-color excitation as a logical operation,” he said.

The work by Rohan and his colleagues has been published in the Journal of Physical Chemistry Letters and is available here.