Designing Molecular Sensors Activated by Hydrogen-Transfer Agents: From Colorimetric to Fluorogenic Hydrogen Detection

The escalating global demand for sustainable and carbon-free energy has heightened interest in hydrogen gas (H₂) as a clean alternative to fossil fuels. However, the intrinsic safety challenges associated with H₂, including its broad flammable range, low ignition energy, high diffusion constant, and lack of odor, underscore the urgent need for sensitive and selective hydrogen sensors. Conventional electrochemical, catalytic, and thermal conductivity sensors, although widely used, often face limitations such as cross-reactivity, instability under varying conditions, and explosion risks in high H₂ environments. To address these challenges, optical sensing platforms have emerged as attractive alternatives due to their high sensitivity, ease of use, and compatibility with remote or point-of-emission monitoring.

This presentation will highlight our recent advances in the optical detection of hydrogen using molecular systems activated by hydrogen-transfer chemistry. We will first discuss the development of a fluorescent sensor based on the commercially available dye azomethine-H (Az-H), enabling indirect detection of H₂ through its reaction with formic acid both in solution and in the solid state. Building on these results, we developed a new hydrogen-transfer-driven sensing platform that couples Az-H with an inorganic activator capable of H₂ activation under ambient conditions. Detailed photophysical studies will be presented to illustrate the effects of H₂ exposure on the fluorescence and absorbance properties of Az-H in the presence of the activator, as well as the system’s sensitivity, selectivity, and transition toward pseudo-solid configurations. Finally, the complementary use of tetrazolium blue as a colorimetric indicator will be introduced, illustrating a broader design framework for hydrogen detection through hydrogen-transfer-induced optical responses.