title: Twisted Hemithioindigo Photoswitches: Solvent Polarity Determines the Type of Light-Induced Rotations.
abstract: Controlling the internal motions of molecules by outside stimuli is a decisive task for the generation of responsive and complex molecular behavior and functionality. Light-induced structural changes of photoswitches are of special high interest due to the ease of signal application and high repeatability. Typically photoswitches use one reaction coordinate in their switching process and change between two more or less-defined states. Here we report on new twisted hemithioindigo photoswitches enabling two different reaction coordinates to be used for the switching process. Depending on the polarity of the solvent, either complete single bond (in DMSO) or double bond (in cyclohexane) rotation can be induced by visible light. This mutually independent switching establishes an unprecedented two-dimensional control of intramolecular rotations in this class of photoswitches. The mechanistic explanation involves formation of highly polar twisted intramolecular charge-transfer species in the excited state and is based on a large body of experimental quantifications, most notably ultrafast spectroscopy and quantum yield measurements in solvents of different polarity. The concept of pre-twisting in the ground state to open new, independent reaction coordinates in the excited state should be transferable to other photoswitching systems.
authors: Department für Chemie, Ludwig-Maximilians-Universität München , D-81377 Munich, Germany.
authors: Sandra
authors: S
authors: Wiedbrauk
authors: Institut für Biomolekulare Optik, Ludwig-Maximilians-Universität München , D-80538 Munich, Germany.
authors: Benjamin
authors: B
authors: Maerz
authors: Institut für Biomolekulare Optik, Ludwig-Maximilians-Universität München , D-80538 Munich, Germany.
authors: Elena
authors: E
authors: Samoylova
authors: Institut für Biomolekulare Optik, Ludwig-Maximilians-Universität München , D-80538 Munich, Germany.
authors: Anne
authors: A
authors: Reiner
authors: Institut für Biomolekulare Optik, Ludwig-Maximilians-Universität München , D-80538 Munich, Germany.
authors: Florian
authors: F
authors: Trommer
authors: Department für Chemie, Ludwig-Maximilians-Universität München , D-81377 Munich, Germany.
authors: Peter
authors: P
authors: Mayer
authors: Institut für Biomolekulare Optik, Ludwig-Maximilians-Universität München , D-80538 Munich, Germany.
authors: Wolfgang
authors: W
authors: Zinth
authors: Department für Chemie, Ludwig-Maximilians-Universität München , D-81377 Munich, Germany.
authors: Henry
authors: H
authors: Dube