Spatial and temporal control of chemical processes

Controlling the where and when of a chemical reaction, rather than just the if, can be an essential component in the successful development of applications. There are a large number of situations in which a predetermined sequence of chemical reaction events might be highly beneficial. In this Review, we examine the development of such spatiotemporal control of chemical reactions. We classify the means of control into either passive or active approaches. The passive approach relies on characteristics inherent to the chosen chemical system in order to predict where and when a reaction will occur. The active strategy, on the other hand, relies on the input of an external stimulus to remotely control the onset of a chemical reaction. Among active methods, we distinguish two different strategies — either remote activation of a reaction or controlled release of chemicals. This versatile toolbox allows spatiotemporal control to be achieved in myriad situations and thus to address some key challenges in chemistry, such as drug delivery. Achieving precise control over when and where a chemical reaction takes place can open the way to a plethora of new applications. This Review gives an overview of progress made in this quest for high spatial and temporal molecular control.