Room Temperature Phosphorescent Oxygen Sensing Performance Enhancedment Of Gadolinium Ion Doped Porphyrin

Oxygen exists in nature mainly in the form of gaseous oxygen and dissolved oxygen and accurate measurement of its concentration is of great significance in the field of aquaculture,environmental protection,and scientific research.Room temperature phosphorescence method(RTP)for oxygen concentration measurement is based on the phosphorescence quenching principle when oxygen exists in the surrounding environment.The RTP method can measure low oxygen concentration accurately with the advantage of none oxygen consumption and well signal-to-noise ratio.However,the deficiency is the photobleaching problem.In this paper,gadolinium ion chelated hematoporphyrin monomethyl ether and sodium porphyrin are used as oxygen probes.The gadolinium chelated porphyrin is widely used for oxygen measurement due to its small toxicity,good stability,large Stokes shift and long phosphorescence lifetime.Whereas,the sensitivity of gadolinium ion-chelated porphyrins in the oxygen measurement is small,and how to improve the sensitivity is important.Therefore,the design and research of enhanced room temperature phosphorescent oxygen sensing performance of gadolinium ion chelated porphyrin were carried out.Researches on the preparation and characterization of gadolinium ion chelated porphyrin.Gadolinium hematoporphyrin monomethyl ether(Gd-HMME)and gadolinium porphyrin sodium(Gd-DVDMS)were synthesized by thermal solvent method,which simplified the synthesis process of gadolinium chelated porphyrin.Gadolinium porphyrin was characterized by absorption spectroscopy.The Gd-HMME and Gd-DVDMS were successfully synthesized by comparing the number and peak position of B band and Q bands of absorption spectra of Gd-HMME,Gd-DVDMS,HMME and DVDMS.The luminescence characteristics of two gadolinium porphyrins were studied,and it was demonstrated that the phosphorescence emission of gadolinium chelated porphyrins originated from the triplet excited state.Researches on the sensitivity enhancement performance of gaseous oxygen concentration measurement was carried out.It is found that the Stern-Volmer curve between the phosphorescence intensity of Gd-HMME filter paper and gaseous oxygen concentration has a nonlinear phenomenon,and the sensitivity of gaseous oxygen measurement was redefined as “a”.The sensitivity of Gd-HMME for oxygen measurement was improved from 6 to 30,that is,the value of sensitivity was increased by 5 times.The reasons for the non-linearity of the Stern-Volmer curve are investigated.The results indicate that the lower Gd-HMME concentration and imidazole concentration play the same role.Due to the decrease of the imidazole concentration,the protection for Gd-HMME was destroyed,resulting in the increase of energy transfer efficiency kq and reaction probability between Gd-HMME and oxygen molecules,thus improve the oxygen sensitivity.Researches on the sensitivity enhancement performance of dissolved oxygen concentration measurement was carried out.The water solubility of Gd-DVDMS was explored,and the calibration curves of between gaseous oxygen and dissolved oxygen concentration were given.The methanol solution of Gd-DVDMS was purified by dialysis to remove the large amount of imidazole added during the synthesis process.The mechanism of the influence of imidazole on the dissolved oxygen sensitivity was analyzed.With the decrease of imidazole concentration,the protection of imidazole on the triplet state of Gd-DVDMS was destroyed,which attribute to the improvement of the interaction rate kq between Gd-DVDMS and dissolved oxygen molecules,resulting in the increase of KSV value and the maximum quenching ratio was increased by 2.6 times.The influence of imidazole concentration on the sensitivity were verified by the absorption and luminescence spectrum.Consequently,a method to adjust the sensitivity was proposed.