The Selective and Sensitive Fluorogenic Detection of Hydrogen Gas Using an Azomethine-H Dye

Hydrogen (H_2(g)) is a viable green fossil fuel alternative, as its combustion yields only water and energy. However, H_2(g) is highly flammable, explosive, and lacks odor. These characteristics warrant sensitive and specific detection methods for its widespread use as an alternative fuel source. Recently, there has been growing interest in the development of H_2(g) sensors, particularly those that are easy to use, environmentally friendly, and sensitive. Here, we show the first example of an optical fluorogenic hydrogen sensing platform, which employs a readily available dye azomethine-H (Az-H, 4-hydroxy-5-(2-hydroxy-benzylideneamino)-naphthalene-2,7-disulfonic acid) and a hydrogen-transferring compound [{Ir(Cp*)(Cl)}₂(thbpym)](Cl)₂ (IrCp*, (Cp* = C₅Me₅^–, thbpym = 4,4′,6,6′-tetrahydroxy-2,2′-bipyrimidine)) to engineer H_2(g) gas selectivity with high sensitivity at room temperature and pressure. This system yields ∼47–fold fluorescence enhancement when exposed to H_2(g) in aqueous solution or ∼2.4–fold in a carboxymethyl cellulose (CMC) hydrogel matrix, with an estimated detection limit of ∼0.5% H_2(g) with no cross-reactivity observed for potentially contaminating gases such as nitrogen (N_2(g)), oxygen (O_2(g)), or air.