Fiber optic lifetime pH sensing based on ruthenium(II) complexes with dicarboxybipyridine

Area of Science:

• Coordination Chemistry
• Materials Science
• Analytical Chemistry

Background:

• Ruthenium(II) complexes are known for their photoluminescent properties.
• Developing robust and sensitive pH sensors is crucial for various scientific and industrial applications.
• Luminescence-based sensing offers advantages in non-invasive and real-time monitoring.

Purpose of the Study:

• To synthesize and characterize ruthenium(II) complexes with phenanthroline ligands.
• To investigate the pH-dependent luminescence properties of these complexes.
• To evaluate their potential for pH sensing applications, including immobilization in optical fibers.

Main Methods:

• Synthesis of ruthenium(II) complexes: [Ru(Phen)(2)Dcbpy]Cl(2) and [Ru(Ph(2)Phen)(2)Dcbpy]Cl(2).
• Characterization of luminescence intensity, emission wavelength, and excited-state lifetime as a function of pH.
• Immobilization of a ruthenium(II) complex onto optical fibers using a sol-gel method.
• Determination of apparent pK(a) values and excited-state lifetimes for protonated and ionized species.

Main Results:

• The luminescence properties (intensity, wavelength, lifetime) of the ruthenium(II) complexes showed a clear sigmoid variation with pH between 3 and 9.
• Apparent pK(a) values were determined to be around 3.6-3.7.
• Excited-state lifetimes varied significantly between protonated and ionized species, indicating sensitivity to pH changes.
• Immobilization in sol-gel matrices yielded pH-sensitive fiber probes with distinct lifetimes for different protonation states.

Conclusions:

• The synthesized ruthenium(II) complexes are effective luminescent indicators for pH sensing in aqueous solutions.
• The sol-gel immobilized complex demonstrates suitability for developing fiber-optic pH probes.
• These materials are well-suited for both intensity and frequency domain interrogation in pH sensing applications.