Light induced transformations in biomembranes Cellular membranes constantly experience remodeling as exemplified by morphological changes during endo and exocytosis. Regulation of membrane morphology is essential for these processes. In this work we attempt to establish a regulation path based on the use of photoswitches exhibiting conformational changes in model membranes namely giant unilamellar vesicles (GUVs). The mechanism of the changes in the GUVs’ morphology caused by isomerization of the photosensitive molecules has been previously explored but still remains elusive. We examine the morphological reshaping of GUVs in the presence of the photoswitch o tetrafluoroazobenzene (F azo) and show that the mechanism behind the resulting morphological changes involves both an increase in the membrane area and generation of a positive spontaneous curvature. First we characterize the partitioning of F azo in a single component membrane using both experimental and computational approaches. The partition coefficient calculated from molecular dynamic simulations agrees with ...