Molecular Strategies to Modulate the Electrochemical Properties of P-Type Si(111) Surfaces Covalently Functionalized with Ferrocene and Naphthalene Diimide.

Abstract

The surface coverage and molecular composition of redox-active molecules anchored on conductive surfaces regulate the kinetic and thermodynamic parameters of charge transfer reactions, providing a means to tune the electrochemical properties of hybrid materials. Herein, anchoring strategies and structural properties of redox-active probes, derived from ferrocene (Fc) and naphthalene diimide (NDI), are shown to regulate the electrochemical properties of functionalized p-doped Si(111) surfaces. Covalent functionalization of hydrogen-terminated Si(111) surfaces with Fc and NDI affords redox-active hybrid interfaces characterized through microscopy, spectroscopy, and voltammetry methods. Molecular design and synthetic grafting strategies modulate the electrochemical properties of the Fc-functionalized Si surfaces with a much higher (ca. 25 times) surface coverage (1.25 × 10-10 mol cm-2) for one-step photografting compared to divergent synthetic routes. Interestingly, the thermal grafting of an alkadiyne followed by "click" reaction with ferrocenyl-azide leads to one of the highest surface coverages (9.97 × 10-10 mol cm-2) of organo-iron reported and a significant anodic shift of the half-potential (>350 mV) compared to photografting methods. Similar experiments with NDI units exhibited electrochemical properties that diverge from those recorded for NDI in solution. The results presented herein offer access to novel redox-active Si interfaces that evidence tunable electrochemical properties of potential interest for microelectronic applications.