Shining light on single molecule dynamics: photon by photon

点击翻译按钮获取中文摘要

Molecules are the smallest building blocks of a material which carry the same properties as the material itself. They are made of atoms joined together in a specific way. If we just consider the most abundant atoms, like carbon, nitrogen, oxygen, hydrogen, silicon and phosphorus, the possible combinations and associated molecular architectures are limitless, with each exhibiting altogether different properties. The way we live today depends on the ongoing development of new molecules, each with a specific functionality, but making these molecules is challenging and can take many years to accomplish. Often, the outcome is a compromise - the molecules we use are the ones that are easiest to make and function acceptably well, but are not necessarily the best for the job. Sometimes the aftermath of such a compromise can be unpredictable and potentially tragic, e. g. side effects in drugs.Renowned physicist and visionary, Richard Feynman once said it would be easy to analyse any complex molecular structure if one could just "look at it and see where the atoms are". But what if we could go a step further and control the way molecules are made? The approach we propose does exactly that. A scanning tunnelling microscope (STM) consists of a sharp needle-like tip, which - much like a vinyl player tracing out the waveform imprinted on a musical record, - allows us to trace out the atomic structure of single molecules. It must be noted, however, that when we go down to the very, very small world of atoms, matter is governed by the laws of quantum mechanics, and it behaves nothing like it does on a large scale. An STM allows us not only to "see" individual atoms, but also to fiddle around with them. And as we do so, we can open up completely new opportunities for design.It is in principle possible for a physicist to use an STM to synthesise any molecular architecture that a chemist describes. But to do this, we must first gain control over the statistical nature of quantum mechanics. This ambitious task is achievable thanks to the recent progress in both our understanding of the natural processes that take place on the nanoscale and in our better technological capability to detect all the different outcomes of chemical reaction dynamics. In our work, we will use an STM in combination with light emission measurements to simultaneously interrogate a single molecule reaction in all of its dimensions - space, time and energy. We will then demonstrate control over the reaction outcome by precisely controlling the relaxation dynamics of the molecule.This research is of great importance to our fundamental understanding of chemical processes. It provides a new route to programming chemical reactions and hence addressing the challenge of making the synthesis of molecules 100% efficient. Moreover, it may open up the future possibility for designing completely new materials with tailored properties.