Organosilicon dimer of BTBT as a perspective semiconductor material for toxic gas detection with monolayer organic field-effect transistorsElectronic supplementary information (ESI) available: AFM images of LB, LS and spin-coated films of BTBT and quaterthiophene dimers; grazing incidence diffraction pattern for spin-coated monolayer film of BTBT dimer; typical transfer characteristics for spin-coated and LB devices; typical transfer characteristics with hysteresis loop; charge carrier mobility

Monolayer organic field effect transistors (OFETs) provide opportunity for ultrahigh sensitivity gas sensor applications due to a strong dependence of OFET key parameters on the environment. However, an impressive combination of both high sensitivity and instantaneous response of such gas sensors can be achieved only on low-defect dense monolayers with high electrical performance. Herein, we investigated monolayer thin film formation of recently developed benzothieno[3,2- b ][1]benzothiophene (BTBT) organosilicon dimer D2-Und-BTBT-Hex by Langmuir-Blodgett, Langmuir-Schaefer and spin-coating methods. For all these techniques, the conditions of uniform low-defect monolayer formation were found. These monolayers were used for preparation of OFET devices, which demonstrated excellent electrical performance with a hole mobility up to 7 × 10 −2 cm 2 V −1 s −1 , a threshold voltage around 0 V and an on-off ratio of 10 5 as well as long-term stability of half-year storage under ambient conditions. Preliminary investigations demonstrated that the monolayer OFETs give an instantaneous response to ammonia at low concentrations (down to 400 ppb). These findings show a great potential of BTBT-based OFETs for large-area sensing device application. Monolayer organic field effect transistors (OFETs) based on novel BTBT dimer demonstrate excellent electrical performance and fast response to ammonia vapours.