Planarizable push-pull systems as mechanosensitive fluorescent probes: focus on turn-on sulfide donors

The objective of this thesis was to design, synthesize and evaluate mechanosensitive membrane probes that operate by a combination of planarization and polarization in the ground state. A suitable twisted oligomeric scaffold was identified first. The monomers of choice turned out to be dithienothiophenes (DTTs), referred to later on as “fluorescent flippers” in the new “flipper probes.” The main topic to this thesis concerned the optimization of donor and acceptor in the new DTT mechanophores. This involved much organic synthesis and culminated in the discovery of the concept of “turn-on donors.” These are donors that act as acceptors in the twisted conformation of the flipper probes to support deplanarization and prevent oxidation and turn into acceptors only upon planarization to support the planar push-pull system. The result is a giant Stokes shift. The promise of maximized mechanosensitivity with “turn-on probes” was then evaluated in membranes, macrocycles and proteins