Excitonic coupling in SAMs of azobenzene-functionalized alkanethiols

Excitonic coupling in SAMs of azobenzene-functionalized alkanethiols

Excitonic coupling in SAMs of azobenzene-functionalized alkanethiols

The functionalization of surfaces with molecular switches is a rapidly growing field in today’s research. Molecules can be used as repeatable building blocks for electronics and sensors and thereby open the perspective to tailor devices on the nanoscale. In this respect self-assembled monolayers (SAMs) have often been considered as ideal platforms to order and align molecules at surfaces. Optical properties and geometric structure of self-assembled monolayers of azobenzenefunctionalized alkanethiols have been investigated by UV/Visible and near edge X-ray absorption fine structure spectroscopy in combination with density-functional theory. By attaching a trifluoro-methyl endgroup to the chromophore both the molecular tilt and twist angle of the azobenzene moiety are accessible. Based on this detailed structural analysis the energetic shifts observed in optical reflection spectroscopy can be qualitatively described within an extended dipole model. This substantiates sizeable excitonic coupling among the azobenzene chromophores as an important mechanism that hinders trans to cis isomerization in denselypacked self-assembled monolayers.

J. Am. Chem. Soc., 2010

funded DFG through Sfb658, Elementary Processes in Molecular Switches at Surfaces