|M.Sc Student||Shritz Rozalia|
|Subject||Preparation and Characterization of Luminiscent Systems for|
Cumulative and Momentary Oxygen Detection
|Department||Department of Chemistry||Supervisor||Professor Yoav Eichen|
|Full Thesis text - in Hebrew|
The detection of molecular oxygen is of prime importance in numerous industries as well as in research. Optical sensors for assessing the momentary as well as the cumulative oxygen concentration were developed and even commercialized in the past decade.
Luminescence quenching of long-lived excited states is the most frequented technique for the determination of momentary oxygen concentrations. The relationship between the oxygen concentration in the sample and the lifetime or intensity of the luminescence of some dyes can be quantified using the Stern-Volmer equation. Colorimetry is usually the method of choice for assessing the time-concentration cumulative exposure to oxygen. Cumulative oxygen sensors report the aggregated exposure to O2. Therefore, they are perfectly suitable for sensing oxygen in MAPs (Modified Atmosphere Packages) for storage of perishable goods.
The goal of this research was to develop means for detection of the cumulative and momentary exposure to oxygen, based on luminescent systems that increase their luminescence upon reacting with oxygen.
The new sensing molecule was designed in light of the PET (Photo Induced Electron Transfer) based luminescence turn-on concept. In PET-based systems the sensing molecule contains a luiminophore and a quencher, also serving as the oxidation site, that are attached to each other in a way that prevents luminescence. Upon a reaction with the target molecules to be sensed, oxygen in our case, the quencher is disabled and luminescence is regained.
This research addressed three different issues.
a) The preparation and characterization of systems for cumulative oxygen detection.
The reaction of novel systems with oxygen was tested. Upon the reaction with oxygen an enhancement of the fluorescence was determined. The prepared systems were well characterized and their oxidation reactions in solution as well as gas-to-phase reactions were observed.
b) Mechanistic studies of the oxidation reaction of the prepared systems. The reaction was found to proceed via photooxidation type II mechanism, meaning that singlet oxygen is produced during irradiation process. It is irreversible, thus allowing cumulative detection.
c) The preparation and characterization of systems for detection of the momentary exposure to oxygen based on the previously prepared systems.
Diphenyl alkyl phosphine oxide, the product of the photooxidation reaction from the previous section was found to be appropriate for this purpose. The sensor molecule showed a relatively high sensitivity to oxygen at the concentration range of 0-20%.