Spiropyran/Merocyanine adsorption on a Gold Surface

Spiropyran is a photochromic, three-dimensional molecular switch which can be converted to Merocyanine, a planar isomer of Spiropyran where the central C-O bond has been broken. The adsorption behavior of a specific molecule, namely naphtho-merocyanine on an Au(111) substrate has been investigated using Scanning Tunneling Microscopy (STM) and computational chemistry methods. The experiments show a strong preference of dimer formation of the merocyanine molecule. Topographical and spectroscopic measurements are used to identify two distinguished configurations, an elongated dimer and a compact dimer. With the help of DFT and Molecular Mechanics calculations these two configurations as well as the specific merocyanine isomer can be identified and energy calculations including adsorption geometries could be performed. This is a first step in investigating possible pathways toward the switching behavior of merocyanine and spiropyran on this substrate.