Stable negative differential resistance in porphyrin based σ–π–σ monolayers grafted on silicon†
Two Si-based hybrid self-assembled monolayers were synthesized by electro-grafting two di-O-alkylated porphyrins as the σ–π–σ systems. The monolayers showed a stable and reversible negative differential resistance (NDR) property at room temperature. The monolayer, fabricated using the porphyrin with fluorophenyl groups was more compact and showed a tenfold peak-to-valley ratio (PVR) relative to the other similar system devoid of the fluorine atoms in the porphyrin moiety. This suggested better pre-organization of the former, possibly by hydrogen bonding through the electro-negative fluorine atoms.