Fluorescent heteroditopic and redox-active sensors for sulfide and pH/Eh

Hydrogen sulfide (H2S) is a poisonous and corrosive gas both found in nature and produced anthropogenically from fossil fuel combustion and landfill sites. When dissolved in water, H2S is primarily found in its anionic form, hydrosulfide (HS ). This anion presents numerous problems, including degradation of sewage infrastructure and corrosion to metal waste containers - notably those used to store nuclear waste. Sensing and monitoring hydrosulfide levels is therefore of significant industrial and public relevance. Previous hydrogen sulfide detection methods suffer from being irreversible, and therefore unsuitable for continuous monitoring purposes. Therefore, one of the aims of this project is to develop fluorescent sensors that are capable of monitoring hydrosulfide levels continuously and reversibly. In recent years, halogen bonding has been demonstrated to be a powerful interaction for the recognition of anionic species, and has shown a desirable selectivity for hydrosulfide over other anions commonly found in water, including chloride. Heteroditopic receptors - receptors possessing two distinct binding sites for the simultaneous recognition of oppositely charged species - have also latterly garnered attention due to their enhanced affinity and selectivity towards charged species relative to their simpler, monotopic analogues. This project seeks to build on these recent developments, by incorporating both a hydrosulfide-binding halogen bonding motif, and also a cation-binding region, into a fluorescent molecular backbone, allowing for the sensing of hydrosulfide salts commonly found in water. Halogen bonding heteroditopic hydrosulfide salt recognition in water is unprecedented, and indeed selective recognition of sulfide in any solvent system remains rare. Therefore, further exploration of this area will lead to a better understanding of the features and requirements of successful hydrosulfide recognition systems. The acidity (pH) and reducing potential (Eh) of water sources is also of critical relevance to infrastructure and industry, due to their considerable impacts on the longevity and stability of crucial materials and components. The application of halogen bonding in pH or Eh chemosensor design is unprecedented, and therefore another aspect of this project is to seek to develop novel halogen bonding chemosensors which respond to pH via sensitive optical methodologies and also demonstrate redox activity for the monitoring of Eh. Overall, this project seeks to facilitate the continuous monitoring of the properties of water sources to improve the durability and safety of important infrastructure exposed to water. Working in collaboration with Radioactive Waste Management, this project falls within the synthetic supramolecular chemistry EPSRC research area.