INVESTIGATION OF REDUCTION EFFECT OF CONCENTRATION QUENCHING OF TRIS(BIPYRIDINE)RUTHENIUM(II) CHLORIDE DYE

A. Yensebaeyeva, graduate student,
O. Lu, graduate student,
I. Irgibayeva, Sc.D., Professor,
A. Mantel, Ph.D.
L.N. Gumilyov Eurasian National University, Astana, Kazakhstan

INVESTIGATION OF REDUCTION EFFECT OF CONCENTRATION QUENCHING OF TRIS(BIPYRIDINE)RUTHENIUM(II) CHLORIDE DYE

Fluorescence concentration quenching (CQ) of organic dyes in solution is a well-known phenomenon that limits their effectiveness and, consequently, the fields of application [1]. Tris(bipyridine)ruthenium(II) chloride (RuBpy) is also known as a photostable dye which is used for chemical and biological research [2–4]. The main drawback of this dye is the low fluorescence intensity, which drops sharply when the limiting concentration is reached, above which CQ is observed.
Our research project is aiming to increase the CQ of RuBpy by using the method of encapsulation of dye into silicon dioxide nanoparticles [5]. The used technique is based on the Stober’s reaction [6].
There were prepared several solution of RuBpy dye of various concentrations in isopropyl alcohol, from diluted to saturated one. The transmittance spectra of prepared solutions are represented in Figure 1.
 

Figure 1 – Transmittance spectra of RuBpy solutions. The concentration of dye: 1 – 6,48×10^-12 mol/l; 2 – 1,16×10^-11 mol/l; 3 – 2,52×10^-11 mol/l; 4 – 5,91×10^-11 mol/l; 5 – 7,83×10^-11 mol/l; 6 – 1,12×10^-10 mol/l; 7 – 1,37×10^-10 mol/l; 8 – 1,66×10^-10 mol/l

In the prepared solutions the Stober’s reaction of the growing silicon dioxide nanoparticles has occurred. Fluorescence and excitation spectra of the solutions were taken before and after the reaction. The optimal concentration of the dye is 7.83×10-11 mol/l at which the fluorescence intensity reaches a peak and the СQ effect is minimal.
The Figure 2 shows the excitation spectra for the most saturated solution before and after the reaction.


Figure 2 - Excitation spectra of RuBpy solutions with a concentration of 1.66 × 10-10 mol/l before the reaction (red curve) and after the reaction (blue curve)

As can be seen from Figure 2, after the main reaction, CQ of the dye is reduced for excitation at the short-wavelength range, in particular for a wavelength of 285 nm, which is responsible for the transition inside the ligand with high energy, i.e. electron transfer from the π-binding to the anti-binding ligand orbital (π → π *) [7]. We explain this fact by the obstructed steric conditions for the formation of aggregates due to the dye molecule is surrounded by a silica shell.

References:
1. Quenching (fluorescence) [Electronic resource]. URL: https://en.wikipedia.org/wiki/Quenching_(fluorescence)#References.
2. Winkler J.R., Gray H.B. Electron transfer in ruthenium-modified proteins // Chem. Rev. 1992. Vol. 92, № 3. P. 369–379.
3. Balzani V. et al. Luminescent and Redox-Active Polynuclear Transition Metal Complexes † // Chem. Rev. 1996. Vol. 96, № 2. P. 759–834.
4. Kamat P. V. Photochemistry on nonreactive and reactive (semiconductor) surfaces // Chem. Rev. 1993. Vol. 93, № 1. P. 267–300.
5. Zhang J. et al. Dye-labeled silver nanoshell-bright particle. // J. Phys. Chem. B. NIH Public Access, 2006. Vol. 110, № 18. P. 8986–8991.
6. Stöber W., Fink A., Bohn E. Controlled growth of monodisperse silica spheres in the micron size range // J. Colloid Interface Sci. Academic Press, 1968. Vol. 26, № 1. P. 62–69.
7. Kalyanasundaram K. Photophysics, photochemistry and solar energy conversion with tris(bipyridyl)ruthenium(II) and its analogues // Coord. Chem. Rev. 1982. Vol. 46. P. 159–244.