A phthalocyanine sensor array based on sensitivity and current changes for highly sensitive identification of three toxic gases at ppb levels

Abstract

A series of cobalt and metal-free phthalocyanine ambipolar semiconductors, MPc[β/α-O(4-CF₃-Ph)₄] (M = Co, 2H) (1–4), are synthesized and fabricated into self-assembled microstructures. The Co[Pc(β/α-OPhCF₃)₄] (1 and 3) molecules formed one-dimensional (1D) nanoribbons (400–300 nm) with a larger width of 1 relative to 3, whereas the H₂Pc[β/α-O(4-CF₃-Ph)₄] (2 and 4) molecules self-assembled into wider microbelts (5–4 μm) with 2 larger than 4, showing the effect of the M center and the substituent positions of the Pc rings on the dimensions of the microstructures. An increased crystallinity is revealed in the order of 4 < 3 < 2 < 1, resulting in an increased conductivity in the same order. Towards NO₂ and NH₃, both positive and negative current changes are found among the sensors 1–4, with the lowest limit of detection (LOD) as low as 3 ppb for NO₂ and 420 ppb for NH₃ from 1, while a positive current response to H₂S is obtained only from 1 with a LOD of 100 ppb, respectively, achieving the best results for the room-temperature detection of NO₂, NH₃ and H₂S gases based on all of the solution-processed phthalocyanine-based sensors reported so far. Accordingly, the sensor responses are dominated by both M-analyst interaction (M = Co, 2H) and conductivity among the sensors 1–4. In particular, different sensor arrays consisting of the sensor of 1 combined with one of the other three sensors of 2–4 are established. NO₂, NH₃ and H₂S gases at ppb levels can be accurately identified by the combination of two parameters, namely current change direction and sensitivity.