Transforming the fluorescent fluorine anion probe from on-off to ratiometric type by a tiny modification on the triarylborane group

Abstract

Based on the electron-deficient property of the pπ orbital in boron atoms, varies of triarylborane-based materials have been designed as the fluorescent probes to detect fluorine anions. However, the strong Lewis acid/base interaction between the probes and F− anions usually quenches the fluorescence, leading to relatively low performance. In this work, two triarylborane-based fluorescent F− anion probes B1 and B2 were developed. Both were highly emissive with fluorescence quantum yields larger than 0.7 and showed impressive sensitivity and selectively to F− anions. The limit of detection (LOD) of B2 was as low as ca. 0.16 µM, which was one of the lowest LOD for F− anions. More importantly, by simply replacing a sp2 hybridized carbon atom in B1 with a sp2 hybridized nitrogen atom to from B2, the responses to F− anions were transformed from on-off to ratiometric fashion. Based on theoretical calculations, this admired transformation was assigned to the significant differences in the distribution of key molecular orbitals, the components of the S1 state and the oscillator strengths between related species.