Diketopyrrolopyrrole-Based Semiconducting Polymer with Both Hydrophobic Alkyl and Hydrophilic Tetraethylene Glycol Chains for Monolayer Transistor and Sensing Application

Functional field-effect transistors (FETs) have received increasing attention in recent years. Herein, it is demonstrated that the incorporation of hydrophilic tetraethylene glycol (TEEG) chains into the diketopyrrolopyrrole (DPP)-based semiconducting polymer (PDPP3T1) can facilitate the formation of polymeric monolayer at the air-water interface, and the resulting field-effect transistors (FETs) show sensitive and selective response toward alcohol vapor. By using the Langmuir-Schaefer method, monolayer and ultrathin films from bilayer to five-layer can be successfully prepared. Interestingly, nanopores with sizes of 50-100 nm are formed within the monolayer film, as observed by using atomic force microscopy. The monolayer FET exhibits relatively high hole mobilities up to 0.014 cm(2) V-1 s(-1), which is among the highest charge mobilities reported for ultrathin film FETs prepared with the Langmuir technique. Moreover, hole mobility increases with an increase in the thickness of the ultrathin film from monolayer to three-layer, and it reaches 0.04 cm(2) V-1 s(-1) for three-layer FETs. A variation of both on-current and off-current is detected for monolayer FET upon exposure to alcohol vapor. The monolayer FET displays ultrahigh sensitivity (down to 1 ppb) and good selectivity toward alcohol vapors, in particular ethanol vapor. This can be attributed to the synergetic effects of the hydrophilic TEEG chains in PDPP3T1 and the nanopores within the monolayers.