(PDAs) were among the first conjugated polymers to be synthesized, and their remarkable properties have been extensively studied since the 1960s. Many of the monomers crystallize in 3D structures or in 2D Langmuir films, and undergo topotactic polymerization (click to see "movie") on UV exposure. The resulting semiconducting polymers exhibit, variously, photoconductivity, non-linear optical response, thermochromism, photochromism and/or solvatochromism. In spite of this extensive research, there is still incomplete understanding of the charge transport properties, and of the structural differences that lead to the various colored phases.

Motivated by early reports of very high charge mobility in some PDA derivatives, and by the desire to examine the possibility of monolayer field-effect transistors (FETs), we have studied several derivatives and refined the processing conditions needed to obtain a PDA monolayer of essentially one phase on a solid substrate.

By pre-patterning an oxidized silicon substrate with source and drain electrodes, a structure suitable to evaluate FET gating was fabricated.

A voltage applied to the silicon substrate increases the conductance between source and drain, demonstrating for the first time that a highly ordered monolayer of conjugated polymer can act as the channel of an FET.