Work Group Prof. Dr. F. Temps

Functionalized Nanoparticles

Functionalized nanoparticles have gained tremendous importance in fundamental and applied sciences because of their unique, size dependent optical, electronic, magnetic and chemical properties with potential application in medical diagnostics, drug delivery, cancer therapy, nanoelectronics and information storage, imaging and super resolution microscopy, sensors, photovoltaics and solar energy conversion, (photo)catalysis, surface coatings or the development of smart materials. In Collaborative Research Centre 677 "Function by Switching" at CAU Kiel, particular interest exists in nanoparticles with surface-bound molecular switches that can be controlled by ultraviolet or visible light. 

  

Azobenzene-functionalized gold nanoparticles

The photoswitching properties of molecules on surfaces are subject to several mechanisms affecting or hindering the outcome. First, dense packing of the surface-bound molecules may leave too little free space for the transformation to proceed, especially when a photo-induced reaction is associated with a large-amplitude structural change. Second, energy transfer either between the attached switches or between the switch and the nanoparticle substrate may lead to a rapid electronic deactivation of the photoexcited molecules and even prevent the reaction altogether. A third major issue arises when a change in properties of NPs upon isomerization of the switches in the ligand shell leads to aggregation of the NPs, which may impede further switching after only a few cycles.

Azobenzene-Functionalized AuNP
 
Functionalized AuNP with a mixed self-assembled monolayer (mSAM) of azothiolate and alkylthiolate ligands.

 

Surface-functionalized gold nanoparticles (AuNPs) carrying a self-assembled monolayer (SAMs) of azobenzene (AB) photoswitches constitute ideal model systems for investigating the photophysical and photochemical dynamics of molecules on surfaces because they can be studied using our entire arsenal of femtosecond spectroscopy methods. Our work thus aims to resolve differences in the photoswitching dynamics of ABs on AuNPs compared to the same ABs in solution.

Important papers:

  • A. Köhntopp, M. Dittner, F. Temps, "Femtosecond Time-Resolved Dynamics of trans-Azobenzene on Gold Nanoparticles", J. Phys. Chem. Lett., 7, 1088 - 1095 (2016). DOI: 10.1021/acs.jpclett.6b00102
  • A. Köhntopp, A. Dabrowski, M. Malicki, F. Temps, "Photoisomerisation and Ligand-Controlled Reversible Aggregation of Azobenzene-Functionalised Gold Nanoparticles", Chem. Commun. 50, 10105 - 10107 (2014).  DOI: 10.1039/c4cc02250e  

  

Controling the fluorescence of semiconductor nanoparticles

In addition to our substantial interest in their dynamics, molecular photoswitches are highly useful tools to modulate and control the fluorescence properties of many types of nanoparticles, especially semiconductor ones. Our work explores a number of interesting applications and tries to unravel the underlying dynamics. Check back for news later ...