Monomer fluorescence intensity

S-2, in which the spacer between the two boronic acids is flexible, has the additional capability of forming excimers. The 1 1 binding of a saccharide leads to an increase in the monomer fluorescence intensity. This increase has two origins the decrease in excimer formation, and the increase in fluorescence quantum yield resulting from suppression of the PET process. The 1 1 complex is formed at low saccharide concentrations, but increasing the concentration leads to the formation of the 1 2 complex, as revealed by the increase in the ratio of the intensities of the excimer band to the monomer band. The selectivity of S-2 was found to be similar to that of S-l. 

Pyrene carboxaldehyde and a series of pyrene carboxylic acids were found useful as fluorescence probes in describing the constitution of inverted micelles of certain calcium alkarylsulfonates in hydrocarbon media. 1-Pyrene carboxaldehyde is a convenient probe for studying the particle sizes of micelles in the region of lOOA. A series of graded probes, pyrene carboxylic acids with varying alkyl chain length, have been used to determine internal fluidity and micro-polarity as a function of distance from the polar core of these Inverted micelles. Pyrene exclmer to monomer fluorescence intensity ratio and fluorescene lifetime provided the means of measurement of internal fluidity and micropolarity, respectively. 

Lateral Mobility(Fluidity) of Sulfonate A and B Micelles. The ratio of excimer to monomer fluorescence intensity of pyrene had previously been used to measure the fluidity of biological membranes (8). The ease of excimer formation was correlated with the fluidity of the membrane. The same principle may be applied to the measurement of fluidity in inverted micelles. To this end, we used three pyrene carboxylic acid probes of varying chain length PVA, PNA and... 

It can be seen that the excimer to monomer fluorescence intensity ratios for the same molar ratio of probe to sulfonate are much smaller in the sulfonate A system than in the sulfonate B system. For both sulfonates A and B, the intensity ratio tends to Increase with the chain length of the carboxylic acid. The variation is distinctly established for sulfonate B micelles, but less so for sulfonate A micelles. The results indicate that the internal fluidity of the micelles decreases from the edge of the polar core to the continuous hydrocarbon medium the gradient is steeper for sulfonate B. 

De Schryver and co-workers u> have confirmed Chandross result for the UV absorbance of l,3-bis(2-naphthyl)propane. Nishijima et al.12) have stated that the absorbance spectrum of meso- and dl-2,4-bis(2-naphthyl)pentane and of the compounds l,3-bis(2-naphthyl)A, where A = propane, butane, pentadecane, and 5-phenylpentane, is similar to the absorbance spectrum of 2-ethylnaphthalene. Finally, an unusual result has been obtained by De Schryver et al.13> for the compound bis(l-(2-naphthyl)ethyl)ether. The meso compound gave a lower value of ID/IM, the ratio of excimer to monomer fluorescence intensities, under excitation at 304 nm relative to excitation at 285 nm, while the dl compound had no such excitation dependence. The UV absorbance spectra of these compounds were not reported, however. 

Ueno et al. also prepared the b i s (2 - n ap h t h y I s u I fe n y 1) - y - CD series in which the naphthyl moieties are very limited in their movement because the linker between naphthalene and CD is only sulfur [37], All isomers of 12(AB), 13(AC), 14(AD), and 15(AE) exhibit only monomer fluorescence due to the rigid linker. It means that the two naphthalene moieties cannot take face-to-face orientation because of the limited flexibility. Although the excimer cannot be used for sensing molecules, Ueno et al. found that the monomer fluorescence intensity increases with increasing guest concentration. Thus, this modified CD series can be used as chemosensors of a different type. 

In the pressure region in which the experiments were performed a linear relation was found between pressure and flux. In Fig. 1 the monomer fluorescence intensity is presented as a function of the stagnation pressure. It was assumed that the deviation from linearity is due to the formation of clusters. The dimer production depends on P, where P is the stagnation pressure. Therefore the measured signal S was fitted in Fig. 1 to the formula... 

Steady state absorption spectra and emission spectra were recorded on a Perkin-Elmer 552 UV-Vis and MPF-44B fluorescence spectrophotometer respectively. The ratio of Ig/I is the ratio of the intensity of excimer (A 480 nm) to monomer fluorescence (A 377 nm). The ratio of I3/I1 is the ratio of the intensity of the pyrene monomer fluorescence intensity of peak 3 (A 384 nm) to peak 1 (A 373 nm). 

Excimer-to-Monomer Fluorescence Intensity Ratio (I /I). In most probe studies using excimer formation, as mentioned above, the excimer-to-monomer fluorescence intensity ratio I /I is used as an experimental criterion (11,17-19). 

From the temperature dependence of the excimer-to-monomer fluorescence intensity ratio I /I, for Py and IPy(3)IPy on reversed-phase Si-C. g, the activation energy E of surface diffusion was determined, using [2]. Values for E of 19 and 40 kJ/mol were found... 

In addition to parinaroyl phospholipids, pyrene fatty acid derivatives may be used. Such phospholipids have a concentration-dependent emission spectrum (Roseman and Thompson, 1980). At low concentrations of the derivative within the bilayer, the fluorescence is maximal at a wavelength below 400 nm. At higher concentrations of the derivative, the excited state monomers can associate with a ground state monomer to form a dimer complex, or eximer, in a diffusion-controlled process. The maximum emission wavelength of the eximer shifts to approximately 470 nm. The ratio of the eximer to monomer fluorescent intensity is proportional to the concentration of the probe molecules within the bilayer. 

The excimer fluorescence has been used to characterize the miscibility of the guest and host polymers [Xie et al., 1993]. Since the excimer forming site concentration depends on the extent of the guest polymer aggregation, the ratio of excimer to monomer fluorescence intensity, is related to blend miscibility. 

SDS sodium dodecyl sulfate STS sodium tetradecyl sulfate SHS sodium hexadecyl sulfate TTAC tetradecyltrimethylammonium chloride CTAC hexadecyltrimethylammonium chloride DMPC dimyristoyl phosphatidylcholine DPPC dipalmitoyl phosphatidylcholine. Exciplex/monomer fluorescence intensity ratio, measured at the exciplex emission maximum (/ ) and at 310 nm (I). 

The fluidity in the neighborhood of probe molecules can be tested by use of probes capable of intramolecular excimer formation. The probe molecules contain the two excimer-forming moieties linked by an alkyl chain. The extent of excimer formation depends on the viscosity of the environment and can be monitored by measuring the excimer/monomer fluorescence intensity ratio. The dependence of this ratio on reciprocal viscosity for the probe molecule dipyrenylpropane is shown in Fig. 18, in which the obtained microfluidities for surfactant systems are indicated. The fluidities decrease in the order SHS microemulsion, SDS, CTAC, Triton X-100 cf. Ref. 167 (for abbreviations see Tables 6 and 7). The same sequence order was found by Kano et al. (68). In systems containing heavy counterions the method leads to data that must be evaluated carefully, since heavy atom interactions may be different with excited monomers and excimers. The intramolecular excimer technique is also useful in biological studies. For instance, Almeida et al. investigated the sarcoplasmic reticulum membrane in which the activity of the Ca -pumping enzyme is modulated by the membrane fluidity (197). 

Figure 18. Excimer/monomer fluorescence intensity ratio 77/ at 30°C of l,3-di(l-pyrenyl)propane [Py(3)Py] as a function of the reciprocal viscosity for a series of hexadecane-liquid paraffin mixtures (curve). The 77/ ratios obtained with Py(3)Py in aqueous micellar solutions of sodium dodecyl sulfate (SDS, 0.1 Af), cetyltrimethyl-ammonium chloride (CTAC, O.OS Af), and Triton X-100 (0.004 Af), and in the microemulsion SHS(M) (see Table 7) are indicated. The fluidities determined were 3.1 mPa s (SHS(M)], 11 mPa s [SDS] 37 mPa s [CTAC], and 105 mPa s [Triton X-100]. Redrawn after Ref. 167.

Aromatic hydrocarbons such as pyrene have also been employed as a luminescence probe of polarity and microviscosity in a variety of organized assemblies (109). Pyrene is a good excimer-forming probe due to the long lifetime of fluorescence and formation of excited-state dimers (excimers) at low concentration. Figure 9 shows an example pyrene luminescence spectrum. The ratio of excimer to monomer fluorescence intensity is often utilized as a measure of pyrene mobility and proximity. The vibronic fine structure of the pyrene monomer is sensitive... 

We have extended the FF model to high trap concentrations using the FPT approximation. In this, the expression for the monomer fluorescence intensity is given by Equation (12), and that for excimer fluorescence by Equation (13) ... 

For solutions of flexible chain polymers two sharp transitions at concentration values and c+ could be easily located in the log-log plot of the excimer to monomer fluorescence intensity ratio < vs the concentration c,... 

An excimer is an electronically excited molecular complex formed between two suitably oriented aromatic rings when one of them has been promoted to an excited state by absorption of energy. The normal characterization parameter is the ratio of the excimer fluorescence intensity to the monomer fluorescence intensity, R, where the monomer refers to the uncomplexed aromatic ring. Of importance for our work is that it is a common feature of the photophysical behavior of the aryl vinyl polymers, as described in a recent review [48]. The objective of this section is to demonstrate the sensitivity of excimer fluorescence to those variables expected to influence the free energy of mixing in polymer blends solubility parameters of the two components, concentration, temperature and molecular weight. 

For both atactic PS in solution [29] and the stereoregular 2,4-DPP s [33], the excimer fluorescence intensity remains constant, then starts to decrease with temperature. This decrease starts at about 300 K for the pol)nner and 330 K for the models. The monomer fluorescence intensity, on the other hand, always decreases with Increasing temperature. Because no increase in monomer fluorescence is observed when the excimer decreases, this has been interpreted as showing that no dissociation to excited monomer occurs [29,33]. 

Effect of PS Molecular Weight. The fluorescence results for 5% PS/PVME blends are shown in Figure 5. The ratio of excimer to monomer fluorescence intensities is given as a function of temperature for monodisperse PS molecular weights ranging from 2,200 to 390,000. The PVME was a polydisperse sample having 47,000. 

Figure 6 Ratio of excimer to monomer fluorescence intensities plotted as a function of 1-Np content in poly(A/l-Np(x)) in aqueous solution. (From Ref. 25.)...

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