Construction of BODIPY-CTAB assembles for ratiometric fluorescence pH measurements in complete water system

• Two BODIPYs were physically trapped inside the hydrophobic core of CTAB micelles.
• The BODIPY-CTAB assembles display ratiometric optical change within the pH of 4–9.
• The pH dependent red/blue optical switch is reversible and repeatable.

Two 6-hydroxyindole-based boron-dipyrromethenes (BODIPYs) have poor solubility and remain essentially nonemissive in water. In this paper, they were physically trapped inside the hydrophobic core of cetyltrimethylammonium bromide (CTAB) micelles, while ensuring solubility of the assembly in water. Due to the hydrophobic character of the micelles core, the two BODIPYs become fluorescent in water as they behave in organic solvents. More importantly, these BODIPY-CTAB assembles display distinct ratiometric optical change within the pH window of 4–9 in complete water system, indicating the capability as ratiometric fluorescent pH indicators. 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.

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