N-Heterocyclic carbene formation induced fluorescent and colorimetric sensing of fluoride using perimidinium derivatives

In this study, two perimidinium derivatives (1 and 2) were designed, synthesized, and developed as efficient fluorescent and colorimetric chemodosisensors for F-in DMSO or more competitive media (DMSO containing 10% water). In the presence of F-, the yellow and non-fluorescent solution of 1/2 became colourless and exhibited strong blue fluorescence. This unique spectroscopic behaviour of 1/2 towards F-was attributed to the formation of N-heterocyclic carbene deprotonated by F-, which immediately reacted with water to give a colourless and fluorescent carbinol. Interestingly, it was found that this carbinol intermediate was unstable and further underwent a redox disproportionation to generate two other optically changed compounds. All the proposed mechanisms for the sensing process have been carefully confirmed by experiments.