Nature controls biological processes, for example, signal transduction, protein function and gene expression, with exquisite spatial and temporal precision. In order to study and understand these processes, an equally precise control element is required. Light is an excellent tool for this purpose, as it can be precisely regulated in timing, location, wavelength, and amplitude, thereby enabling high-resolution optical control of biological processes. The developments of optogenetic tool sets are revolutionizing many aspects of science, most importantly neurobiology. We are developing related optochemical tools that are based on our ability to combine synthetic chemistry with cell and molecular biology.