Shining light on single molecule dynamics: photon by photon

分子是材料的最小组成部分，它与材料本身具有相同的性质。它们是由原子以一种特殊的方式结合在一起构成的。如果我们只考虑最丰富的原子，如碳、氮、氧、氢、硅和磷，可能的组合和相关的分子结构是无限的，每一种都表现出完全不同的性质。我们今天的生活方式取决于新分子的不断发展，每一个都有一个特定的功能，但制造这些分子是具有挑战性的，可能需要很多年才能完成。通常，结果是一种妥协——我们使用的分子是最容易制造和功能可接受的，但不一定是最适合这项工作的。有时，这种妥协的后果可能是不可预测的，甚至可能是悲剧性的，例如药物的副作用。著名物理学家和梦想家理查德·费曼（Richard Feynman）曾经说过，分析任何复杂的分子结构都很容易，只要人们能“看着它，看看原子在哪里”。但如果我们能更进一步，控制分子的形成方式呢？我们提出的方法正是这样做的。扫描隧道显微镜（STM）由一个尖锐的针尖组成，就像黑胶唱片机追踪音乐唱片上的波形一样，可以让我们追踪单个分子的原子结构。然而，必须指出的是，当我们深入到非常非常小的原子世界时，物质是受量子力学定律支配的，它的行为与在大尺度上的行为完全不同。STM不仅可以让我们“看到”单个原子，还可以摆弄它们。当我们这样做的时候，我们可以为设计开辟全新的机会。原则上，物理学家可以使用STM合成化学家描述的任何分子结构。但要做到这一点，我们必须首先掌握量子力学的统计性质。这一雄心勃勃的任务是可以实现的，这要归功于我们对发生在纳米尺度上的自然过程的理解的最新进展，以及我们更好的技术能力来检测化学反应动力学的所有不同结果。在我们的工作中，我们将使用STM和光发射测量相结合，同时询问单个分子反应的所有维度-空间，时间和能量。然后，我们将通过精确控制分子的弛豫动力学来证明对反应结果的控制。这项研究对于我们对化学过程的基本认识是非常重要的。它为化学反应编程提供了一条新途径，从而解决了使分子合成100%高效的挑战。此外，它可能为设计具有定制性能的全新材料开辟了未来的可能性。

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.