'On-off-on' fluorescent indicators of pH windows based on three separated components

Area of Science:

• Analytical Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Fluorescent indicators are crucial for monitoring chemical environments.
• Developing selective and responsive sensors for specific analytes like pH is an ongoing challenge.
• Ternary systems offer complex interactions for novel sensing mechanisms.

Purpose of the Study:

• To develop novel "on-off-on" fluorescent indicators for specific pH windows.
• To investigate the use of ternary systems involving metal ions and ligands for fluorescence sensing.
• To characterize the pH-dependent behavior of a Coumarin 343-based sensor.

Main Methods:

• Synthesis and characterization of a ternary system comprising Cu2+, a tetraaza ligand, and Coumarin 343.
• Spectroscopic analysis (fluorescence emission) to determine indicator response.
• pH titration to study the variation of fluorescence intensity with pH.

Main Results:

• The ternary system exhibited an "on-off-on" fluorescence response.
• An inverse bell-shaped variation of emission intensity with pH was observed.
• The observed response is attributed to the interplay of Coumarin 343 protonation, coordination to Cu2+, and displacement by OH-.

Conclusions:

• The developed ternary system effectively functions as a ratiometric fluorescent pH indicator.
• This approach provides a new strategy for designing sophisticated fluorescent sensors.
• The "on-off-on" behavior allows for sensitive detection within defined pH ranges.