Welcome to the Research Group of Henry Dube!





  • Molecular Machines




Immer vorwärts, nie zurück

Damit sich Moleküle wie Motoren verhalten, dürfen sie sich nur in eine Richtung bewegen. Ob das funktioniert, hängt davon ab, ob in den Molekülen Asymmetrie vorliegt. Diese molekularen Motoren bewegen sich mit Frequenzen im Kilo- und Megahertzbereich; Licht gibt ihnen die Energie dafür.  

published in Nachrichten aus der Chemie.

Sunlight Powered kHz Rotation of a Hemithioindigo Based Molecular Motor

Photodriven molecular motors are able to convert light energy into directional motion and hold great promise as miniaturized powering units for future nanomachines. In the current state of the art, considerable efforts have still to be made to increase the efficiency of energy transduction and devise systems that allow operation in ambient and non-damaging conditions with high rates of directional motions. Especially the need for ultraviolet light to induce the motion of virtually all available light-driven motors hampers the broad applicability of these systems. We describe here a hemithioindigo-based molecular motor, which is powered exclusively by nondestructive visible light (up to 500 nm) and rotates completely directionally with kHz frequency at 20 C. This is the fastest directional motion of a synthetic system driven by visible light to date permitting materials and biocompatible irradiation conditions to establish similarly high speeds as natural molecular motors.

open access in Nature Communications.


  • Functional Supramolecular Systems 


Photocontrol of Polar Aromatic Interactions by a bis-Hemithioindigo Based Helical Receptor

The first example of a bis-Hemithioindigo (bis-HTI) based molecular receptor was realized. Its folding and selective binding affinity for aromatic guest molecules can precisely be controlled by visible light and heat. The thermodynamically stable state of the bis-HTI is the s-shaped planar Z,Z-configuration. After irradiation with 420 nm light only the E,Z-configuration is formed in a highly selective photoisomerization. The E,Z-isomer adopts a helical conformation because of the conscious implementation of repulsive sterical interactions. The E,Z-configured helix is able to recognize electron poor aromatic guests exclusively via polar aromatic interactions and also distinguishes between regioisomers. After heating the Z,Z-configuration is completely restored and the aromatic guest molecule is efficiently released. 

 published in Chemistry - A European Journal.

  • Photochemistry and Photophysics


Twisted Hemithioindigo Photoswitches: Solvent Polarity Determines the Type of Light-Induced Rotations

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 mutual 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 (TICT) 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.

 published in J. Am. Chem. Soc.


Hemithioindigo - an Emerging Photoswitch

Hemithioindigo (HTI) is an emerging photoswitch with many advantageous properties compared to the commonly used photoswitches like azobenzenes, spiropyranes, or dithienylethenes. In this DIGEST the syntheses, physical and photophysical properties of HTI photoswitches and mechanistic explanations for the latter are reviewed. Emphasis will be placed on those distinct properties that render HTIs into unique phototools. Additionally, a broad variety of applications ranging from supramolecular to biological chemistry is presented to highlight the great potential of HTIs as upcoming, alternative photoswitches.

 published in Tetrahedron Letters.

Making Fast Photoswitches Faster - Using Hammett Analysis to Understand the Limit of Donor-Acceptor Approaches for Faster Hemithioindigo Photoswitches


Hemithioindigo (HTI) photoswitches have a tremendous potential for biological and supramolecular applications due to their absorptions in the visible in conjunction with ultrafast photoisomerization and high thermal bistability. Being able to rationally tailor their photophysical properties for a specific application is the key to exploit the full potential of HTIs as photoswitching tools. In this work we used time-resolved absorption spectroscopy and Hammett analysis to discover an unexpected principal limit to the photoisomerization rate for donor substituted HTIs. Using stationary absorption and fluorescence measurements in combination with theoretical investigations, we offer a detailed mechanistic explanation for the observed rate limit. An alternative way of approaching and possibly even exceeding the maximum rate by multiple donor substitution is demonstrated, which gave access to the fastest HTI photoswitch reported to date.

 published in Chemistry - A European Journal.




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