Attaching Electronically Active Oligoanilines to Silicon Surfaces

Diazonium salt-functionalized oligoanilines have been synthesized and assembled on hydride passivated silicon surfaces for subsequent incorporation into hybrid molecule−silicon device architectures. The targeted oligoanilines were synthesized using Buchwald/Hartwig Pd-catalyzed coupling reactions. A methodology using N-tert-butoxycarbonyl (Boc) protecting groups was essential to prevent N-nitroso formation during the diazotization step and to prevent rapid air oxidation and decomposition of the products. The molecules were assembled on silicon surfaces to form monolayer films, and thermal removal of the Boc protecting groups was achieved by heating the films to 215 °C for 4 h under argon. Single-wavelength ellipsometry verified the desired monolayer formation. X-ray photoelectron spectroscopy analysis confirmed the loss of the Boc groups and formation of the requisite oligoaniline monolayers. Assembly of 4 in a Molepore electronic test bed device followed by thermalization and retesting indicated that the current was doubled and a larger hysteresis was obtained after removal of the Boc protecting groups, thus underscoring the efficacy of this two-step assembly process. This study provides a route to interface the highly desirable electronically switching oligoanilines to the surface of highest relevance in the electronics industry, namely silicon, via the sequential Boc-based syntheses, diazonium assembly and final film thermolysis.