Bodipy-based dyes for ionic-liquid-based optical carbon dioxide sensors

When ionic liquids come in contact with CO2 gas, their polarity and viscosity increase. Owing to these properties, ionic liquids containing organic dyes, which can change their optical properties depending on their surrounding polarity and viscosity, have recently been applied in portable CO2 optical sensors. Although ionic–liquid-based CO2 optical sensors have excellent sensing properties, the optimal organic dyes for ionic–liquid-based CO2 optical gas sensors have not been extensively investigated. Hence, we synthesized and characterized four 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based dyes (PTPBDP, MTPBDP, TPABDP, and TPAMBDP) to explore the optimal structure for liquid-based CO2 optical sensors, with intramolecular charge transfer (ICT) and aggregation-induced emission (AIE) investigated. In addition, the synthesized dyes were applied to an ionic liquid, with their optical properties measured to analyze and compare their detection abilities and selectivity toward CO2 gas. As the CO2 concentration increased, all sensors, except TPAMBDP, showed changes in the optical properties in the visual and fluorescence channels. This approach facilitates the development of a portable sensor capable of detecting CO2 across diverse environmental conditions, showcasing its potential for versatile application in monitoring and analysis tasks. We believe these results provide insights into the design of organic dye structures for ionic liquid-based CO2 optical sensors.