Optical control on the nanoscale via photoresponsive compounds

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Molecular photoswitches undergo a light-triggered transformation between states with different physicochemical properties, which offers a highly selective, spatiotemporally precise and non-invasive way of nanoscale control. Therefore, photoswitches have become extremely attractive for various applications in chemistry and biotechnology. Nevertheless, the application of photoswitches is relatively rudimentary. Selectivity and efficiency are typically achieved via exhaustive search of appropriate substituents, and photoswitches are triggered via simple excitation fields. Moreover, the application of photoswitches is generally unidimensional, i.e. photoswitches are implemented to control single reactions or properties.Previously, we studied the photochromism of various photoswitches and large photoresponsive constructs and investigated their potential for control at the molecular level. Particularly intriguing aspects of our research are i) the observation of coherent wavepacket motion during the excited state dynamics of photoswitches and ii) the detection of different interactions between the subunits of multiphotochromic compounds (excitonic coupling, steric hindrance, etc.). To address these phenomena, we built a transient absorption set-up for pump-dump/repump-probe and coherent control experiments.Within the new project we will employ our new set-up to investigate the role of coherent vibrational motions in the photochemistry of photoswitches. The experiments will reveal the reactive vibrational modes which will aid the rational design of tailored photoswitches. Further, using multipulse experiments we will study the presence of reactive and non-reactive pathways to gain insight into the complex reaction mechanisms of photoresponsive systems. With the help of multipulse excitation schemes, we will also investigate the intricate molecular interactions between the constituents of multiphotochromic system. Moreover, such excitation schemes will allow us to perform optical programming of the state of multiphotochromic compounds to demonstrate their potential as molecular logics. These type of molecular logics would afford control in multiple dimensions to achieve complex control scenarios.In addition to these projects, we will continue with the development of novel photoswitch designs. We will explore the properties of azoheteroarenes and hydrazones as ultrafast photochromic oscillators, which are of interest for various applications ranging from nanoscale muscles and motors, through information processors, to photopharmacology. We have also initiated work on chiral photoswitches to exploit this molecular property for exerting optical control. Finally, we are working on combining ultrafast spectroscopy and time-resolved crystallography to reach in-depth understanding of the dynamics and the mechanism of operation of photoswitchable biomimetic protein ligands.