Construction Of BODIPY-CTAB Assembles For Ratiometric Fluorescence PH Measurements In Complete Water System

Organic dyes are the most widely used fluorescent probes for indication of pH. However, most of these fluorescent dyes have poor solubility in water and the hydrophobicity greatly limits their applications. It is still a challenge to develop pH indicators in100%aqueous system.Our lab has developed a6-hydroxyindole-based BODIPY with straightforward phenol/phenolate interconversion by varying pH value, showing phenol/phenol ate dependant emission blue-red switching. Therefore, this BODIPY can be an excellent ratiometric pH indicator in aqueous-organic mixed media. However, the neutral form of6-hydroxyindole-based BODIPY is nonfluorescent and unstable in complete aqueous systems.With the idea of developing new ratiometric fluorescent probes for indication of pH in100%aqueous system, herein we introduce a simple and general route to encapsulate6-hydroxyindole-based BODIPYs into water soluble surfactant micells for sensing pH. The hydrophobic BODIPYs1and2can be physically trapped inside the hydrophobic core, while ensuring solubility of the assembly in water. Due to the hydrophobic character of the micells core, BODIPYs1and2becomes fluorescent in water as it behaves in organic solvents. More importantly, these BODIPYs trapped in CTAB micells displayed distinct ratiometric optical change within the pH window of4-9in complete water system, indicating the capability of1or2in CTAB micells as a ratiometric fluorescent pH indicator. Furthermore, the pH dependent red/blue optical switch is reversible and can be repeated for many cycles by alternative exposure to acidic and basic media.