A vapochromic chemosensor based on a Zn(II) salen-type complex for the detection of volatile organic compounds

Volatile Organic Compounds (VOCs) are molecules, in liquid or solid form, which due to their high vapor pressure, can easily evaporate at room temperature. Some VOCs are responsible for air pollution and can be hazardous to human-health.1 Thus, the development of feasible and low-cost chemosensors is relevant for the direct monitoring of VOCs in specific environments. In this context, the use of chemosensors based on Lewis acidic Zn(II) salen-type complexes can represent a promising strategy. The sensing mechanism implies the formation of stable penta-coordinated adducts between the Zn(II) salen-type complexes and VOCs having Lewis basicity, such as nitrogenous-containing VOCs (N-VOCs), involving significant colour and luminescence changes giving rise to characteristic vapochromism.2 In this contribution, we report on the unique thermo- and vapochromic properties of a Zn(II) salen-type derivative from the 2,3-diaminomaleonitrile, Zn(salmal), with 5,5´-tert-butyl- bulky substituents on the salicylidene rings. In particular, both the synthesized and anhydrous complex (i.e., the latter achieved by solvent evaporation under nitrogen conditions) show a marked vapochromism if exposed to saturated vapours of various VOCs.3 Interestingly, we also demonstrate the possibility to fabricate simple and low-cost paperbased sensors (PBSs) able to discriminate N-VOCs by well-defined spectroscopic and distinct naked-eye colour changes (Figure 1). This contribution has been partially funded by European Union (NextGeneration EU), through the MUR-PNRR project SAMOTHRACE (ECS00000022).