Xanthene-based Fluorescence Turn-on Probe for Highly Acidic pH Range in Aqueous Solution

Area of Science:

• Chemical Sensing
• Fluorescence Spectroscopy
• Molecular Probes

Background:

• Highly acidic environments require sensitive detection methods.
• Fluorescence-based probes offer advantages in sensitivity and selectivity.
• Photoinduced electron transfer (PET) is a key mechanism for designing responsive molecular probes.

Purpose of the Study:

• To develop a novel xanthene-based fluorescent probe (Xanth-NPr) for detecting highly acidic environments.
• To elucidate the mechanism of fluorescence modulation based on photoinduced electron transfer (PET).
• To evaluate the probe's performance, including its pH sensitivity and selectivity.

Main Methods:

• Synthesis of a xanthene-based probe (Xanth-NPr) incorporating a dipropylaniline group.
• Design based on the photoinduced electron transfer (PET) principle.
• Spectroscopic analysis (fluorescence) to study probe behavior under varying pH conditions.
• Theoretical calculations and synthesis of a model probe (Xanth-M) to validate the PET mechanism.

Main Results:

• Xanth-NPr exhibited quenched fluorescence in neutral/moderately acidic conditions.
• A strong red fluorescence (592 nm) was observed in highly acidic pH due to PET inhibition.
• The probe showed a linear fluorescence response to pH between 1 and 4.1, with a pKa of 2.72.
• The fluorescence of Xanth-NPr was unaffected by biologically relevant cations.

Conclusions:

• Xanth-NPr is a sensitive and selective fluorescent probe for highly acidic environments.
• The observed fluorescence turn-on behavior is effectively controlled by the PET mechanism.
• The probe's stability in the presence of cations suggests potential applications in biological systems.