Enhancing the electronic-coupling and conductivity of a monolayer film of ferrocenyl molecules by Pd and Cu doping

Abstract

Improving the conductivity and modulating the electronic structure of molecular films holds significance in using them in thin film-based electronic applications. In this paper, we create a surface-confined metal–organic network (SMON) with electrochemically active ferrocene functional units and Pd/Cu. The SMONs are generated using monolayer films of two custom designed ferrocenyl molecules (3-ferrocenyl propenoic acid (FcC3) and 5-ferrocenyl pentadienoic acid (FcC5)) on a graphite surface. While the microscopic structure of the molecules within the film remains comparable before and after doping, due to the incorporation of Pd and Cu in the 4-coordinated site of the carboxyl dimer of FcC3/FcC5, the conductivity shows a sharp increase upon doping the FcC3/FcC5 film with Pd and Cu. The electronic structure calculation of the FcC3/FcC5 dimer with a metal reveals a strong reduction in the HOMO–LUMO gap compared to the hydrogen-bonded dimers. This suggests a strong intermolecular electronic coupling of molecules through the Pd and Cu metal within the monolayer film, thereby reducing the barrier for electron/hole transport.