Kinetically controlled photoinduced electron transfer switching in Cu(I)-responsive fluorescent probes

Area of Science:

• Chemical Sensing
• Photochemistry
• Molecular Probes

Background:

• Copper(I)-responsive fluorescent probes often exhibit incomplete emission recovery.
• This phenomenon raises questions about potential quenching mechanisms.
• Understanding probe behavior is crucial for accurate copper(I) detection.

Purpose of the Study:

• Investigate the photophysical behavior of copper(I)-responsive probes.
• Determine if copper(I) engages in adverse quenching pathways.
• Clarify the mechanism of fluorescence switching in these probes.

Main Methods:

• Detailed photophysical studies on thiazacrown receptor-fluorophore probes.
• Time-resolved fluorescence decay and femtosecond pump-probe experiments.
• Variable temperature (1)H NMR and quantum chemical calculations.

Main Results:

• Optimized fluorescence enhancement up to 29-fold for copper(I) binding and >500-fold for protonation.
• Identified three distinct emissive species in copper(I)-saturated probes.
• No evidence of transient Cu(II) species formation, ruling out reductive quenching.

Conclusions:

• Copper(I) does not engage in adverse quenching pathways.
• Fluorescence switching is kinetically controlled, not limited by electron transfer.
• Dynamic equilibrium involving solvent coordination influences probe behavior.