Dual-responsive phosphorus-based fluorescent sensors: synthesis and selective metal sensing of pyrazolyl phosphine oxides

Despite a wealth of previously reported frameworks for fluorescent metal sensors, there are few examples of phosphorus-based fluorophores being used in metal sensing applications. Here, we report the synthesis and characterisation of a new family of pyrazolyl-phosphine oxides and their use in metal sensing applications. The mechanism of their formation has been probed in detail with both computational and experimental studies, rationalising the selectivity of the reaction. Their use as dual-responsive fluorescent metal sensors is then demonstrated, with ‘turn-off’ and ‘turn-on’ responses observed for Fe3+ and Al3+, respectively. These systems exhibit good selectivity, large Stokes shifts, and submicromolar limits of detection, and will open new avenues in phosphorus-based fluorophores and metal-sensing applications.