Chemisorption vs. physisorption in perfluorinated Zn(II) porphyrin–SnO2 hybrids for acetone chemoresistive detection

In this study, the integration of SnO2 with a perfluorinated Zn(II) porphyrin derivative, namely ZnTPPF20CN, was explored as a strategy to enhance the performance of chemoresistive sensors toward gaseous acetone detection. The ZnTPPF20CN molecule was specifically designed with an ethynylphenyl-cyanoacrylic anchoring group and a benzothiadiazole (BTD) spacer, enabling its chemisorption onto the SnO2 surface. Hybrid materials containing three different ZnTPPF20CN-to-SnO2 ratios (1:4, 1:32, 1:64) were fabricated and tested for acetone detection at 120 °C, both under dark conditions and LED illumination. The sensing behavior of these hybrids was compared with that of previously studied SnO2 composites, incorporating physisorbed, unsubstituted ZnTPPF20. Among the tested ratios, the 1:32 ZnTPPF20CN/SnO2 demonstrated superior acetone sensitivity compared to its unmodified counterpart, despite showing a lower intrinsic conductivity in air and a reduced electron transfer efficiency. Density functional theory (DFT) calculations provided insights into the possible anchoring modes and interfacial electronic interactions, helping to rationalize this counterintuitive observation. The enhanced sensing response was attributed to a more favorable balance between charge injection and the availability of SnO2 electronic states, facilitated by the chemisorbed anchoring of ZnTPPF20CN. Overall, our findings highlight the importance of molecular engineering, particularly in terms of molecular design, loading ratio, and anchoring mechanism, in modulating charge dynamics and optimizing the sensing efficiency of porphyrin/SnO2 nanocomposites.