Self-Assembled Monolayers with Charge-Transfer Groups: N-Mercaptoalkyl Tetrathiafulvalenecarboxylate on Gold

The syntheses of n-mercaptoalkyl tetrathiafulvalenecarboxylates (n = 16, 12, 11, 8) and the electrochemical and structural properties of self-assembled monolayers derived from these compounds are described. Self-assembled monolayers of the title compound on gold electrodes displayed voltammetric responses characteristic of the TTF subunit. Infrared reflectance absorbance spectroscopy suggests that the monolayer consists of liquid-like alkyl chains. Exposure of a monolayer of 1 (n = 16) to tetracyanoquinodimethane (TCNQ) results in formation of a monolayer containing a novel charge-transfer unit nominally described as Au-S-(CH₂)₁₆-OC(=O)-TTF+TCNQ-. Spectroscopic data suggest that the TCNQ-anion adopts an orientation parallel to the gold substrate.