Nonlinear optical chemosensor for sodium ion based on rhodol chromophore

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Photophysics

Background:

• Development of fluorescent probes for ion detection is crucial for chemical and biological sensing.
• Two-photon excited fluorescence (TPEF) offers advantages like deeper tissue penetration and reduced photobleaching compared to one-photon fluorescence.
• Rhodol derivatives and crown ethers are known for their fluorescent properties and ion-binding capabilities, respectively.

Purpose of the Study:

• To design and synthesize a novel fluorescent sensor for sodium cation (Na+) detection.
• To investigate the spectroscopic properties, particularly two-photon absorption (2PA), of the synthesized probe.
• To evaluate the probe's sensitivity, selectivity, and mechanism of action for Na+ sensing.

Main Methods:

• Synthesis of rhodol derivatives linked with aza-crown ethers (1-aza-15-crown-5 and 1,10-diaza-18-crown-6) using condensation and Buchwald-Hartwig reactions.
• Characterization of electronic and spectroscopic properties, including linear absorption and two-photon absorption (2PA) spectra.
• Investigation of the probe's response to Na+ binding in acetonitrile (CH3CN) using fluorescence spectroscopy.

Main Results:

• An efficient synthetic route to novel rhodol-aza-crown ether conjugates was established.
• The synthesized rhodol derivatives exhibited strong absorption and fluorescence with well-resolved vibronic bands.
• The probe functionalized with 1-aza-15-crown-5 demonstrated high sensitivity and selectivity for Na+, showing a significant "turn-on" fluorescence enhancement (approx. 10-fold) due to quenched electron transfer and increased 2PA.
• The probe showed minimal response to other metal ions.

Conclusions:

• A novel "turn-on" fluorescent probe for Na+ based on rhodol and aza-crown ether has been successfully developed.
• The probe utilizes enhanced two-photon excited fluorescence (TPEF) upon selective Na+ complexation.
• This sensor holds promise for sensitive and selective detection of sodium ions in chemical sensing applications.