Influence of sol-gel composition to the HPTS-ion pair spectroscopic characteristicsYakhshilikova L.J.,D.Sayimova, Kh.Sh.Tashpulatov*

Master student; *Research-Scientist

Samarkand State university named after A.Navoi, Department of Natural Sciences,

Samarkand, Uzbekistan

E-mail:

Pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt – HPTS) has been used for optical pH sensors very successfully[1,2]. Recently this indicator found an application a wide range of gas sensors with different ion pairs[3-6]. For using optical sensor ion-pair approach were used to encapsulate highly polar HPTS into hydrophobic support matrices with a phase transfer reagents[7]. As phase transfer reagents may be used quaternary ammonium bases as teraoctylammonium hydroxide(TOAOH), tetrabutylammonium hydroxide(TBAOH) and cetyltrimethy-lammonium hydroxide(CTAOH). Similar work also reported that Fluorescence of HPTS is quenched by trisodium citrate in cationic micellar media and the quenching rate constant decreases with increase in hydrophobic chain length of the surfactants[8].

We have immobilised pyranine in the different hydrophobic sol–gel derived glass by the use of a phase transfer reagents, creating the lipophilic dye–counter-ion pairs that allows the polar dye to be incorporated in the organically modified silica (ormosil) glass and studied pyranine-ion pair spectral characteristics. Depending on external microenvironment of the doped pair, its spectral characteristics changes greatly due to composition of the sol-gel precursors.

It is very interesting optical properties of pyranine in different sol-gel and lipophilic base. Because incorporating ion-pair in sol-gel is very complex task. During the sol-gel preparation for ion-pair one must take into account factors affecting dye fluorescence.

Films dried in ambient temperature have strong influence of solvents MtOH and EtOH, and they have blue shift in spectra.

In general to develop sol-gel glass for gases the following parameters must be kept in control and it requires accurate calculations and measurements:

Solubility of ion pair in precursor.

Not all alkoxides are suitable for this purpose. Examples contain fluorinated alkoxides.

Sol-gel glass must be hydrophobic and ion impermeable. Glasses prepared from pure TEOS and TMOS are not suitable choice. Also there must not be any chemical interaction between alkoxide chain and carbon dioxide. Amino group containing precursors are not desirable.

Solvent concentration also affects to pyranine fluorescence.

Lipophilic base concentration indicates the sensor sensitivity and stability. On the other hand without accurate calculations preparation transparent film is difficult, base concentration increasing results rapid gelation.

In this study we reported piranine-ion pair fluorescence spectra in various organic and organic-inorganic xerogels. The pronounced changes in the ratio of the protonated form and the deprotonated form of pyranine represent a rather sensitive means of characterizing the environment of the dopant molecule in various cured sol-gel systems.

References

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