Pyrrolyl-silicon compounds with different alkyl spacer lengths: Synthesis, electrochemical behavior and binding properties

- Pyrrolyl-silicon compounds with variable length of alkyl spacer.
- Hydrolyzed oligomeric domains responsible of n-type charge transport.
- Propyl spacer best for OH-π stabilizing interactions and stratification.

This work reports a joint experimental-theoretical investigation of pyrrolyl-silicon compounds with different alkyl spacers, namely propyl, butyl and hexyl side chains carrying silicon-based end groups. For the electrochemical study, the monomers with methoxysilyl end groups spaced through butyl and hexyl chains were ad-hoc synthesized. Structurally different oligomeric domains are promoted during electropolymerization as a result of irreversible hydrolysis of methoxy end groups by acid intermediate σ-oligomers. The onset of OH-π stabilizing interactions and the charge pinning action of silanol promotes mixed n-p doping behavior of the hybrid films. The more important charge trapping in the case of propyl spacer is attributed to effective (through bond) inductive effects and conformational restrictions. MD simulations of chemisorption of hydrolyzed oligo-pyrroles onto γ-Al2O3 surface confirmed the propyl spacer as the optimum alkyl chain length for stratification and interpenetration of adsorbed hybrid layers.