Flipper-TR^® was introduced to image membrane tension in living cells. Targeting strategies to study processes with the fluorophore located in specific membranes are emerging.

In this thesis, strategies to target the fluorophore to early endosomes (EE) were explored. Using weaker acids bearing ammonium cations, the endolysosomal network could be targeted. With careful tuning of the pK_a values of the headgroups attached to the fluorophore, tracking rules were discovered in this study. Probes with higher pK_a values lead to better staining of EE, due to protonation at the higher pH inside the EE. The first series of EE flippers was based on differently substituted benzylamines and later extended to flippers mimicking amino acids Lysine and Arginine. These new flipper probes were used to study the initial stages of endocytosis.

Secondly, the central mechanosensitive bond of the flipper probe was modified by introduction of alkyne bond(s), and first spectroscopic studies performed.