Study On Room Temperature Phosphorescence Properties And Oxygen Sensing Performance Of Gadolinium Hematoporphyrin Monomethyl Ether

Oxygen is the most abundant element in the earth’s crust. The detection of molecular oxygen is crucial in many fields. Porphyrins are macr ocycle compounds and widely exist in nature. Quantum yields of triplet state formation of porphyrins are generally high. However, phosphorecence emission can not be produced for porphyrins at room temperature as the transiton is spin-forbidden. Some metalloporphyrins(porphyrins doped with metal ions) can emit room temperature phosphorescence(RTP). Because phosphorescence can be effectively quenched by oxygen, RTP is widely used in oxygen sensing. In this thesis, we studied the synthesis, RTP properties of gadolinium coordinated hematoporphyrin monomethyl ether(Gd-HMME), the mechanism of RTP emission from Gd-HMME, and the application of Gd-HMME RTP in oxygen sensing.Synthesis and spectral properties of rare earth ions coordinated porphyrins w ere investigated. Several rare earth ions coordinated HMME were synthesized based on solvothermal method with imidazole as molten solvent; multiple charaterization methods were performed to certify that rare earth metall oporphyrins are synthesized sucessfully; Luminescence properties of these metalloporphyrins were studied. Among metalloporphyrins including samarium, europium, gadolinium and ytterbium coordinated HMME, only Gd-HMME has relatively strong RTP emission. It was demostrated that energy of triplet state of HMME was quenched by other rare earth ions such as samarium, europium, and ytterbium.Luminescence properties of Gd-HMME and the mechanism of gadolinium doping induced room temperature phosphorescence from porphyrin were studied. Photophysical parameters were determined. The molar extinction coefficient was measured to be 2.53× 105 M-1 cm-1, fluorescence quantum yield was obtained as 5× 10-4, quantum yield of triplet state formation was determined to be 80(5)%, phosphorescence quantum yield of Gd-HMME was obtained as 1.4%. Here, we demonstrate that the mechanism of RTP induced by Gd3+ from hematoporphyrin HMME is due to the mixing of singlet(S) and triplet(T) states; the direct absorption corresponding to transition from S0 to T1 was observed, which indicates the existing of states mixing; the spin-forbidden transition between S and T states was partly allowed due to the states mixing. Besides, because of the large energy gap between the excited and ground states of Gd3+(larger than 32 000 cm-1), energy in triplet state of Gd-HMME can not be quenched.The influence of oxygen on Gd-HMME RTP on filter paper was studied. It was found that RTP of Gd-HMME can be quenched effectively by oxygen; it was demonstrated that the intensity Stern-Volmer plot is nonlinear in the whole oxygen concentration range; the lifetime plot has similar changing trend; the intensity plot is a little higher than the lifetime plot reflecting the existence of static quenching; data analysis indicates that the static quenching rate constant is unchanged and the percent of static quenching is about 35% ±3% in the whole range of oxygen concentration; the nonlinear intensity and lifetime plots perfectly satisfy the nonlinear solubility model; this indicates that the downward response is related to the nonlinear solubility of oxygen.Different types of oxgen sensors based on Gd-HMME RTP were designed and established. A novel oxygen sensing system based on direct intensiy of Gd-HMME RTP was developed. The intensity Stern-Volmer plot was found to be approximately linear for oxygen concentration from 10 k Pa to 100 k Pa. Fast response time, recovery time(t↓, 0.4±0.2 s; t↑, 1.4±0.2 s) and high photostability were achieved based on direct intensity method. However, it was found that oxygen sensing properties of this system can be affected by the fluctuations of excitation light intensity. To raise stability of oxygen measurement, ratiometric oxygen sensing system based on ratio of filter paper fluorescence to Gd-HMME RTP was developed. Performance parameters for this oxygen sensing systems are obtained. Fluctuation was achieved to be less than 0.1 k Pa. The response time was determined to be about 4 s. These results indicate that this system can be used for oxygen detection in the whole range and is especially accurate for very low oxygen concentrations.