Semiconductor quantum dots are inorganic nanoparticles which, because of their unique size-dependent electronic properties, are of high potential interest for the construction of functional nanodevices. Photoinduced electronand energy-transfer processes between quantum dots and surface-bound molecular species offer versatile strategies to implement functionalities such as luminescence sensing and switching. In this article we discuss the general principles underlying the rational design of this kind of multicomponent species. Successively, we illustrate a few prominent examples, taken from the recent literature, of luminescent chemosensors and switches based on quantum dots derivatized with redox- or photo-active molecular species.