Bent-Core Liquid Crystal-Based Heterojunctions as Gas Sensors

Taking advantage of the filmogenic properties of liquid crystal materials, bilayer heterojunction devices are built by combining them with a molecular semiconductor. Herein, the construction of a novel type of heterojunction sensor by employing bent-core liquid crystals (A1, A2, B1 and C-1C3) as a sublayer with lutetium bisphthalocyanine (LuPc₂) as a common top layer is achieved. Thanks to the modified drop casting method employed to deposit the sublayers, the resulting heterojunction devices exhibit a smooth surface, the morphology of the sublayer determining that of the top layer. All prepared devices are sensitive to ammonia, with a limit of detection below 10 ppm for C1, C2, and C3-based heterojunctions, even down to 2 ppm for C2-based devices, which is more than satisfactory for controlling ammonia levels in industrial working environments. Moreover, the C3-based device shows the shortest response time (t₉₀ = 30 s), which is suitable not only for air quality monitoring but also for applications like security alarm systems. All presented sensors operate at ambient temperature (20 °C) and humidity (45%).