Macromolecular aggregation and electrochemical behavior of pyrrolyl-, anilynyl- and thiophenyl-silicon compounds as precursors for thin hybrid films

Aniline, pyrrole and thiophene substituted with methoxysilyl propyl side chains were investigated by means of spectroscopic and electrochemical techniques. The effect of hydrolysis and ex-situ irradiation of solutions prepared in different solvent mixtures, containing either methanol or methylacetate in excess, was considered also. The development of stable intermediate species in solution is governed by intramolecular polarization of the hydrolyzed monomer rather than by ex-situ photoxidation or electro-oxidation of the monomer head group. Cooperative non-covalent OH-π interactions between the electron deficient silanol (SiOH) and the electron rich aromatic π system leading to mixed- n-p type redox behavior of the hybrid films are confirmed for the case of N-substituted pyrrolyl-silicon derivative. Less efficient interactions of the more basic N-AnSi derivative result from the deprotonation and self-condensation of SiOH, being supported by the prevalent p-type charge transport of the related hybrid film. For the case thiophenyl-silicon derivatives, charge trapping manifesting n-type redox behavior dominates for the case of α-substituted thiophene rather than for the parent β-substituted derivative but with jellification, indicating effective OH-π stabilization of σ-coupled α,α' dimer structures by a short-range intramolecular mechanism. The establishment and modulation of constructive OH-π interactions determine the macromolecular aggregation and redox behavior of the hybrid films. The diverse properties exhibited by the hybrid precursors support different protection mechanisms against corrosion.