A Study Of Sensitized/Quenched Room Temperature Phosphorescence And Its Analytical Application

This dissertation includes seven parts, introduction, experimental section, serisitized/quenched room temperature phosphorescence(RTP) in normal micelles, sensitized/quenched RTP in reversed micelles, sensitized RTP of α-bromonaphthalene(α-BrN) by benzophenone in aerated β-cyclodextrin(β-CD) solution, β-CD induced RTP in aerated solutions, enzyme-amplified lanthanide luminescence spectrometry.In chapter 1, the advance of RTP, the principles of RTP and energy transfer, sensitized/quenched RTP and its analytical application have been reviewed.In chapter 3, (1)the solubilization site of the triplet energy acceptor biacetyl in normal micelles is studied by quenched RTP. The results indicate that biacetyl is located in the head group-water interface and /or likely to be lined up along the alkyl chains of the surfactant's aggregates but its carbonyl group is close to the head group of surfactant. So, if donor is located in the head group-water interface where biacetyl is solubilitized, enhanced energy transfer is observed. (2)The suggestion that micelle organizes the donor and acceptor molecules into a discrete volume region, facilitates the energy transfer and enhances the intensity of sensitized RTP has been demonstrated. The results indicate that the intensity of sensitized RTP is correlative with the Poisson distribution and determined by the value of PDless × PAless which is theprobability of less donor and less acceptor occurred in the same micelle. (3)A new method mat the determination of biacetyl can be done by the quenching of the RTP of α-BrN-sensitized RTP of biacetyl in CTAB micelles is presented. First, CTAB micelles can facilitate triplet-triplet energy transfer and enhance the phosphorescence emission of α-BrN; second, CTAB micelles act as a quencherthat quenches biacetyl-phosphorescence sensitized by α-BrN. The sensitivity for the determination of biacetyl is determined by the triplet-triplet energy transfer rate, kET, between α-BrN and biacetyl. The kET is determined to be1.76×109(mol/l)-1s-1In chapter 4, (1)the properties and aplication of reversed micelles have been comprehensively summarized. (2)A surfactant with α-naphthylacetate counterion, dodecylammonium α-naphthyiacetate (DA+NAA-) has been synthesized. The sensitized biacetyl RTP by α-naphthytacetic acid or DA+NAA- in reversed micelles of AOT/C6H12/H2O is studied and the resultsshow that the RTP intensity of biacetyl is enhanced about 13 times than that observed in aqueous SDS micelles. Factors including the concentration of AOT solubilized water as well as donor and acceptor concentration that may influence the sensitized biacetyl phosphorescence are also examined. The absorption spectra and characteristics of luminescence as well as microviscosity data are used to elucidate the factors that affect sensitized phosphorescence. The intensity of sensitized biacetyl phosphorescence in AOT reversed micells is determinated by the lifetime of sensitized biacetyl, energy transfer efficiency and the Poisson distribution. For α-naphthytacetic acid, no remarkable influence of water content on the intensity of sensitized biacetyl phosphorescence is observed because the effects of both decreasing in microviscosity and increasing in radius of inner core of reversed micelles offset each other. Since the α-naphthylacetate moiety is associated with the DA+ surfactant, it is anchored to the head group in reversed micelles of AOT where biacetyl is soiubillzed. The remarkable influence of water content on the sensitized phosphorescence of biace(?)yl has been observed with the increase of water content. It is not important factor that the change of microviscosity affects the intensity of biacetyl phosphorescence sensitized by DA+NAA- with the increase in W(=[H2O]]/[AOT]]). Increasing W results insno facilitation for thecollision between donor and accepter and in the decrease of energy transferefficiency. It indicates that the more intensely sensitized biacetyl phosphorescence should be observed by using low water contents. The detection limit of biacetyl by using DA+HAA- as the donor is about three times lower than that by using NAA as the donor. It indicates that DA+NAA- is more efficient donor than NAA. (3)A significant enhancement of sensitized room temperiture luminescence has been observed using lanthanide Tb3+ as energy acceptor in AOT reversed micelles at low AOT concentration and W value, and weak Tb3+ emission has been observed in CTAB reversed micelles. The results indicate that Tb3+ ions are strongly bound to the sulfonate group of the AOT surfactant. Because Tb3+ emission is quenched by the high frequency OH vibrations of the surrounding water molecules, the loss of Tb3+ emission in high AOT concentration and W value suggests that the Tb3+cation retains water in its coordination sites. The quenching process is static quenching. The low AOT concentration and W value should be reconmmended for obtaining high sensititivity in analytical application. The fluorescence intensity of theophylline does not change as the concentration of Tb3+ is altered. The results support the energy transfer toTb3+ is from the triplet state of the donor. (4)When comparing the W dependence of the spectra with the pH dependence of the spectra and the W dependence of luminescence intensity of Tc-Eu3+ or Tc with the pH dependence of luminescence intensity, it should be noted that the property of water in reversed micelles at low water content is very similar to that of the alkaline solution. This phenomenon has been discussed in terms of strong hydration of the counterions Na+ and the polar headgroup of AOT at low W and the formation of a bulk-like(but not equal to) water core at higher W. Since both probes, Tc-Eu3+ or Tc, are charged and hydrophiiic, it is expected that both probes will be located between the interface and the center of the water pool. When the value of W is less than 6, all water molecules are bound to the Na+ counterions and polar headgroups of AOT, and become more strongly polarized with a gradual decrease of W, therefore, Tc and Tc-Eu3+complex appear to probe the nature of the "bound" water. The less the value of W, the more effective the water polarization becomes. At low water content such as w=1.5, a water molecule behaves like a OH" ion. The results obtained show that the apparent pH of the water pool in reversed micelles at W=1.5-2.0 is ca.9. The properties of water pool in reversed micelles can be utilized for sensitive detection of tetracycline and analogues without addition of alkali.In chapter 5, the luminescence properties of α-BrN in areated aqueous p-CO solution is studied when benzophenone is intruduced to the system. The results show that the phosphorescence enhancement is induced by benzophenone as both sensitizing and space-filling agent. The affecting factors on room temperature phosphorescence have been studied. The method has been applied to the detection of a-BrN in artificial mixture containing a- and p-BrN, naphthalene, phenanthrene.In chapter 6, (1)intense phosphorescence is observed when c-hexane is induced to aqueous solutions containing α-BrN and β-CD. The results indicate that the kinetic process of the inclusion of α-BrN within the β -CD cup is more favourably induced by c-hexane than by c-hexanol or 2-methyl cyclohexanol. The presence of dynamic quenching in the formation process of ternary complex may simply reflect the ability of the c-hexane to regulate the interaction of α-BrN with β-CD, rather than simply fill the voided regions left by α-BrN in the β-CD cavity. The inclusion of α-BrN in β-CD is increased in the presence of c-hexane (K=1000 M-1 in the absence of c-hexane and k=12470 M-1 in the presence of c-hexane as compared to that in the presence of c-hexanol and 2-methyl cyclohexanol where K=1045,1646 M-1, respectively). It indicates that c-hexane has more tendency to associate with the β-CD/α-BrN complex as compared to c-hexanol or 2-methyl cyclohexanol. Polarization and lifetime analysis show that the phosphorescence enhancement induced by c-hexane is related to its effectiveness in enhancing rigid microenviroment of a-BrN in p-CD and shielding photoexcited a-BrN from oxygen. (2)The properties of mixedorganized media of β-CD and surfactant are investigated by using a-BrN as a RTP probe. Obtained results show a ternary complex of α-BrN/β-CD/surfactant is formed within β-CD cavity bellow the critical micelle concentration(CMC), exhibiting intense phosphorescence. This is interpreted in terms of favorable effects produced by aggregation of the surfactant monomers at the open ends of β-CD torus, probably smaller end, and/or partial inclusion of alkyl chain of surfactant. As a consequence, the cavity of β-CD is effectively "capped", leading to much more extremely rigid and hydrophobic environment for α-BrN, and effectiveness in shielding photoexcited α-BrN from oxygen. Enhanced RTP observed for SDS, TX-100 and Tween 20 indicates that head group of surfactant signifacantly affects the formation of inclusion complex and RTP intensity induced. The decrease in RTP intensity indicates the aggregation and micelle formation of surfactants are induced by β-CD when the concentration of surfactant is bellow the CMC. Results indicate that the head group of surfactant binds to the the open ends of β-CD torus in the surfactant/β-CD inclusion complex, making different kinds of surfactant aggregate at the same concentration. When the concentration of surfactant is above the CMC, α-BrN is displaced from the β-CD cavity and subsequently incorporated into the interior of micelles, leading to the quenching of RTP because of the less rigid microenvironment and the higher concentration of oxygen in the interior of micelles than in the cavity of β-CD. Conclusions drawn from sensitized RTP data suggest that the phenyl moietyl of TX-100 be located inside the β-CD cavity at low concentration and migrated from the inside to outside of β-CD cavity with addition of more surfactant.In chapter 7, enzyme-amplified lanthanide luminescence(EALL) spectrometry using horseradish peroxidase(HRP)-terbium-p-hydroxybenzoic acid system has been studied. This method has also been used for detection of HRP and tuberculosis antibody. It seems to be more suitable for bioanalytical applications.