Absorption of light brings molecules into an activated state. From this state radiative processes can occur, but much more interesting are the nonradiative, dark processes in which the photon energy is transformed into other forms such as mechanical and chemical energy. We aim to control these light-to-activity pathways as they allow us to use photon energy to drive targeted applications such as energy conversion, photocatalysis, photon-driven molecular nanotechnology, as well as optogenetics and photopharmacology.
Key to tailoring photoactivity are studies of the potential energy surfaces of electronically excited states. This is not trivial because photoactivity is generally associated with (ultra)fast conversions of energy. Using eye-catchers from molecular nanotechnology, health care, and various areas where photochromic compounds are employed, we have shown in recent years how ‘slow’ spectroscopies can map the excited-state potential energy surfaces and reveal the dynamics that occur on these surfaces. This is exciting as there is a huge amount of photoresponsive systems that so far have been deemed inaccessible because of their short excited-state lifetimes. There is thus still much to be learnt on the dark side of the forces that act upon molecules after light absorption!