Tunable optical properties of bipyridine dithiol molecules self-assembled on gold substrate

Abstract

Using density functional theory calculations, we study the effect of intermolecular cross-linking and metal ion inclusion on the electronic and optical properties of 5,5’-bis(mercaptomethyl)-2,2’-bipyridine (BPD) molecules self-assembled on gold substrate. The contribution of the molecules to the density of states of the system near the Fermi level becomes more pronounced after cross-linking due to the delocalization of the electronic states towards the molecules. Consequently, the absorption intensity in the infrared and visible ranges of the spectrum enhances after the cross-linking. The other optical parameters of the system (such as refractive index and reflectivity) is also affected by the cross-linking induced structural changes. Optical properties of self-assembled BPD molecules can further be improved by intercalating metal ions which get encapsulated between the pyridinic units of the molecules and create new absorption sites in the visible and UV ranges of the spectrum. These findings can be useful in tuning optical properties of different materials using molecular self-assembly approach.