An in cellulo study of the ultrafast excited state processes in the paradigm molecular light switch [Ru(bpy)2dppz]2+ by localized pump-probe spectroscopy is reported for the first time. The localization of [Ru(bpy)2dppz]2+ in HepG2 cells is verified by emission microscopy and the characteristic photoinduced picosecond dynamics of the molecular light switch is observed in cellulo. The observation of the typical phosphorescence stemming from a 3MLCT state suggests that the [Ru(bpy)2dppz]2+ complex intercalates with the DNA in the nucleus. The results presented for this benchmark coordination compound reveal the necessity to study the photoinduced processes in coordination compounds for intracellular use, e.g. as sensors or as photodrugs, in the actual biological target environment in order to derive a detailed molecular mechanistic understanding of the excited-state properties of the systems in the actual biological target environment.

The developments in high‐resolution microscopy play a challenging role in understanding the fundamental processes in molecular and cell‐biology as well as material research. The most desired feature of any optical microscopy technique is the ability to perform in‐depth scanning of specimens and to distinguish extremely small organelles and their dynamics in the nanometer range. To answer a large variety of questions in all areas of biological and material research, it has become imperative to improve the spatial and temporal resolution of optical microscopes. However since the nineteenth century when Ernst Abbe first established the limit of an optical system to resolve two objects – the Abbe diffraction limit – the scientists have been struggling to approach nanometer resolution by defying the diffraction limit. These continued efforts have led to the development of novel super‐resolution technologies in microscopy that are discussed in this review.