Research Highlights

Optically Programmable Devices

We have been creating optically addressable thin-film transistors by blending photoswitchable charge traps into the organic semiconductor.
Original work with semiconducting polymer:
Nature Chemistry 4, 675 (2012)
High-density, non-volatile, flexible memories:
Nature Nanotechnology 11, 769 (2016)
Light-emitting transistors for displays:
Nature Nanotechnology 14, 347 (2019)

Photocontrolling Chemical Equilibria

We have been achieving remote control over reversible covalent bonds between two molecular entities, enabling us to shift dynamic covalent equilibria with light.
Photoswitchable furans and Diels-Alder adducts:
Angew. Chem. Int. Ed. 53, 8784 (2014)
Use of the system to control thermal healing:
Nature Communications 7, 13623 (2016)
Light-driven C=N condensation/hydrolysis:
Nature Chemistry 10, 1031 (2018)

Remote-controlled Catalysts

We have been able to create photoswitchable catalyst systems spatio-temporal control over bond formation.
Initial work on photoswitchable piperidines:
Angew. Chem. Int. Ed. 47, 5968 (2008);
J. Am. Chem. Soc. 131, 357 (2009)
Photoswitching ring-opening polymerization:
Nature Catalysis 1, 516 (2018)
Reviews:
Angew. Chem. Int. Ed. 49, 5054 (2010)
Chem. Soc. Rev. 43, 1982 (2014)
Chem. Commun. 55, 4290 (2019)

Solar Oscillators
 
We have been able to convert sunlight directly into oscillatory movement by embedding our all-visible tetrafluorazobenzene photoswitches into liquid crystalline polymer thin films.
Nature Communications 7, 11975 (2016)

This effect has been used to fabricate active surfaces that can be used to direct single cell response by light of different wavelengths.
Small 14, 1803274 (2018)



Improving Photoswitches

We have been optimizing various photochromic systems, including:
Azobenzenes addressable in the visible range:
J. Am. Chem. Soc. 134, 20597 (2012)
and by indirect two-NIR-photon-excitation:
Angew. Chem. Int. Ed. 55, 1544 (2016)
and via (photo)redox-catalysis:
J. Am. Chem. Soc. 139, 335 (2017)
Chem 4, 1740 (2018)
Diarylethenes with improved fatigue resistance:
J. Am. Chem. Soc. 137, 2738 (2015)
Angew. Chem. Int. Ed. 55, 1208 (2016)
and addressable by orthogonal stimuli:
Chem. Sci. 4, 1028 (2013)
Acylhydrazones with readily tunable properties:
J. Am. Chem. Soc. 137, 14982 (2015)
N-Arylated indigos as red photoswitches:
J. Am. Chem. Soc. 139, 15205 (2017)
Dihydropyrene One-Photon NIR-photoswitches:
Angew. Chem. Int. Ed. 57, 1414 (2018)

Single Molecular Wires

We have been creating lengthy and defect-free conjugated polyfluorenes via our on-surface polymerization route and could measure the conductance of one and the same molecule as the function of its length.
Initial work:
Science 323, 1193 (2009)
N-doped graphene nanoribbons:
Angew. Chem. Int. Ed. 52, 4422 (2013)
Flexible alternating donor-acceptor polymers:
Nature Communications 6, 7397 (2015)

On-surface Polymerization

We have been developing a method to generate covalent 1D and 2D polymers by an in-situ polymerization process directly on a noble metal surface.
Pioneering work:
Nature Nanotechnology 2, 687 (2007)
Hierarchical growth and surface templation:
Nature Chemistry 4, 215 (2012)
On-surface polymerization has been used to generate single molecular wires (see above) and characterize their conductance in-situ on the single molecule level.

Switch Arrays on Surfaces

We have been discovering the electric-field driven switching of azobenzenes on surfaces and exploited this phenomenon to create periodically ordered switch arrays (switching lattice).

Electric field driven switching:
J. Am. Chem. Soc. 128, 14446 (2006)
Switching array:
Nature Nanotechnology 3, 649 (2008)

Photoswitchable Foldamers

We have been incorporating azobenzene photochromes into specific locations in the backbone of helical foldamers to trigger the helix-coil transition by light.
Initial work:
Angew. Chem. Int. Ed. 45, 1878 (2006)
Quantitative switching:
Angew. Chem. Int. Ed. 50, 1640 (2011)
Sequence-switch-unfolding relationships:
Chem. Sci. 4, 4156 (2013)
Cooperative switching:
Chem. Eur. J. 18, 10519 (2012)
Control over unfolding pathway:
Angew. Chem. Int. Ed. 52, 13740 (2013)
Review:
Chem. Commun. 52, 6639 (2016)

Photoswitchable Rigid Rods

We have been preparing polyazobenzene rods that exhibit near quantitative photoisomerization associated with reversible large changes in aspect ratio, leading for example to (de)aggregation.
Angew. Chem. Int. Ed. 50, 12559 (2011)
Visualization at single molecule level:
ACS Nano 12, 11987 (2014)
Design principle: The decoupling approach:
J. Phys. Chem. B 115, 9930 (2011)

(Self)regulating Solar Energy Conversion

We have been able to dynamically control the life-time of the charge-separated state in a tetrathiafulvalene-diarylethene-fullerene triad by light thereby providing a mechanism for (self)regulation in prototypical artificial photosynthetic systems.

Angew. Chem. Int. Ed. 52, 13985 (2013)




Clickates and Clickamers

We have extensively been exploiting the 1,2,3-triazole moiety as a structure-directing building block to design chemoresponsive tridentate ligands, foldamers as well as shape-persistent folded dendrimers.
Clickates: Chem., Eur. J. 13, 9834 (2007); Chem. Eur. J. 16, 10202 (2010)
Clickamers: Angew. Chem. Int. Ed. 47, 4926 (2008); Chem. Eur. J. 17, 1473 (2011)
Click dendrimers: Chem. Commun. 47, 10578 (2011); Chem. Eur. J. 18, 5837 (2012)

Organic Nanotubes based on Foldamers

We could prepare organic nanotubes based on hollow helically folded polymers either by covalent intramolecular crosslinking or non-covalent intrastrand hydrogen-bonding.

Covalently crosslinked foldamers:
Angew. Chem. Int. Ed. 42, 6021 (2003)
Non-covalently stabilized foldamers:
J. Am. Chem. Soc. 134, 8718 (2012)