Exploring the range of applicability of anisotropic optical detection in axially coordinated supramolecular structures

Ensuring the highest accuracy in determining the molecular assembling and the preservation of the chemical and physical properties of the molecules during the growth of organic layers requires a real-time monitoring of film formation. In this respect, optical techniques are preferred since they result in minimum organic film damage. Among these techniques, Reflectance Anisotropy Spectroscopy (RAS) proved to be the one with the highest sensitivity due to the development of intrinsic anisotropies in the optical response of molecular films, where molecular packing is driven by Van der Waals interactions. Recently, we proposed an original strategy to enable the growth of organic films via molecular self-assembly through highly directional coordination bonds. Herein, we consider a straightforward supramolecular structure employing axial bonds, based on the 1:1 assembly of a Co porphyrin (CoTPP) and a linear ligand (DPNDI). This system is characterized by a rather isotropic structure that might, in principle, result in a weak RAS signal. Therefore, in the present work, we critically assess the range of applicability of such a spectroscopy. A number of other surface science techniques, including Low Energy Electron Diffraction (LEED), photoemission spectroscopies (PES and IPES) and Atomic Force Microscopy (AFM) is employed to fully characterize the axially coordinated molecular film.