Excimer to monomer intensity ratio

Figure 4. Density-dependent excimer-to-monomer intensity ratios (W m) for 100 /xM pyrene in sub- and supercritical C02 at several temperatures, (symbol, Tr) ( , 1.00) (v, 1.01) (t, 1.02) ( , 1.05).

Dependence of the observed excimer to monomer intensity ratio on polystyrene concentration for PS/PVME blends cast from tetrahydrofuran (circles) and toluene (squares) with the fluorescence spectra measured before (open symbols) and after (filled symbols) annealing at 383 K for 10 hours,... 

Having established the existence of the excimer emission of NDI based polyurethanes in solution, and realizing that the intramolecular excimer forming naphthyl carbamate groups are located on the backbone of the polymer, it becomes apparent that an excellent opportunity exists for chain conformational studies as a function of solvent. Figure 10 shows the steady-state fluorescence spjectra of NDI-650 in four solvents with distinctively different solvating power. In each case (curves a-d) both monomer and excimer emission are observed however, tlie ratios of excimer to monomer emission reflect conformational differences of the NDI-650 polymer in the solvent employed. The excimer to monomer intensity ratio... 

Pyrene groups were attached to poly(ethylene glycol) (PEG) at both chain ends to allow pyrene excimer fluorescence to be used as a molecular probe of the complexation between PEG and poly(acrylic acid) (PAA). The excimer to monomer intensity ratio, was... 

To distinguish the two types of excimers clearly a solution of 1% of PEG (both chain ends labeled by chromophores) and 99% of PEG (unlabeled) was also prepared, fixing the total polymer concentration to be 1x10 M. Under this condition, only intramolecular excimer is formed because the excimer to monomer Intensity ratio, I /I, was observed to be constant regardless of small variation of PEG (labeled) concentration in the mixture with unlabeled PEG. We assumed that this allowed the behavior of an individual PEG chain to be examined as discussed in the following section. Furthermore, fully labeled PEG chains in 1x10 M... 

Figure 2 Change in the intramolecular excimer to monomer intensity ratio with the addition of PAA at 303K.

Figure 5 Change in the Intermolecular excimer to monomer intensity ratio with the addition of PAA at 303K. It was calculated by the subtraction of data in Figure 2 from those in Figure 4.

Noticeably, the presence of three linked and proximate fluorophores led to the formation of excimers upon irradiation of a metal free solution of 8 in MeOH/water (4 1, v/v). In particular, the strong excimer band at 485 nm (excimer-to-monomer intensity ratio = 17) does not vary over the 2-8 pH interval. At pH > 8 the emission is quenched according to a sigmoidal profile (see Figure 12). 

I) Dependence of the second excimer to monomer intensities ratio 1 d z /I m of poly(methoxy-4-vinylnaphthalene)(PMVN) in polystyrene matrix on the... 

Excimer to Monomer Intensity Ratio. Our approach toward the determination of this information is to focus on the configurational behavior of the pyrene-terminated PEG. Two sets of experiments were performed to separate the intramolecular behavior of the isolated Py-PEG-Py chains from the intermolecular interactions that occur between labeled PEG chains. First, we performed photostationary fluorescence measurements of IJI for fully labeled PEG as a function of the molar ratio of the poly(carboxylic acid) to that of the PEG. These results will contain both intermolecular and intramolecular contributions to the excimer fluorescence. Next, we performed analogous measurements with the same total amount of PEG but with only 1% having pyrene labels. The selection of the relative amount of the tagged polymer is somewhat arbitrary, but it appears to be sufficiently low to provide a reasonable approximation to the behavior of the isolated, labeled PEG chain. These fluorescence results are then subtracted from those for the fully tagged system, leaving just the intermolecular contribution. 

Figure 5. Excimer to monomer intensity ratio relative to that in free solution for Py-PEG-Py 4250) (+) and Py-PEG-Py 8650) (A) as a function of the number of colloidal silica particles available per chain on average. All initial solutions were in the dilute (intramolecular) regime before the addition of...

ABSTRACT. Excimer fluorescence is developed as a quantitative probe of isolated chain statistics and intermolecular segment density for miscible and immiscible blends of polystyrene (PS) with poly(vinyl methyl ether) (PVME). Rotational isomeric state calculations combined with a one-dimensional random walk model are used to explain the dependence of the excimer to monomer intensity ratio on PS molecular weight for 5% PS/PVME blends. A model for a three-dimensional random walk on a spatially periodic lattice is presented to explain the fluorescence of miscible PS/PVME blends at high concentrations. Finally, a simple two-phase morphological model is employed to analyze the early stages of phase separation kinetics. 

Figure 5. Temperature dependence of the photostationary excimer to monomer intensity ratio for 5% PS/PVME blends. The PS molecular weights are shown by each curve. Taken from Figure 1 of reference 50.

Fig. 2. Effect of molecular weight of the aryl vinyl polymer on the probability that an absorbed photon leads to excimer decay (1-M) divided by the probability of monomer decay M, This is directly proportional to the observed ratio of integrated excimer to monomer intensities. Reproduced from Reference 2A.

The experimental method to assess the phase behavior is to measure the ratio of excimer to monomer intensity, la/lm- Samples of the polymer blend are cast on sapphire disks at thicknesses of the order to 10-25 pm, and the fluorescence spectra are obtained. In a study of the excimer fluorescence of poly(2-vinyl naphthalene) (P2VN) in polystyrene, the monomer emission peak at 337 nm was compared with the excimer emission peak at 398 nm [334]. The ratio of the peaks versus polystyrene molecular weight is illustrated in Fig. 5.32 (a and b). Phase separation (at 0.3 wt% P2VN addition) was observed at PS Mn of 17,500. It was noted that the results show the onset of phase separation before any visual phase separation was observed. 

Fluorescence Measurement Fluorescence spectra were measured on a Spex Fluorolog 212 spectrofluorometer equipped with a 450 W xenon arc lamp and a Spex DM1B data acquisition station. Spectra were recorded in the front-face illumination mode using 343 nm as the excitation wavelength. Single scans were performed using a slit width of 1.0 mm. PDA fluorescence emission spectra were recorded from 360 to 600 nm, with the monomer and excimer fluorescence measured at 376.5 and 485 nm, respectively. Monomer and excimer peak heights were used in the calculation of the ratio of excimer to monomer emission intensities (Ie/Im). Excitation spectra were recorded from 300 nm to 360 nm and monitored at 376.5 and 500 nm for the monomer and excimer excitation, 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. 

Although the theoretical study of EET in polymer systems has led to considerable recent advances, we choose in the second section of this paper to take a somewhat more pragmatic approach to the study of phase separation kinetics. To do so, we temporarily set aside any consideration of the details of any particular EET model and simply rely on a fundamental relationship between the ratio of the excimer to monomer emission intensities, and the... 

Dependence of the ratio of relative intensity of excimer to monomer fluorescence, le/Ij,/ on the pH of aqueous solutions of PMA. 

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... 

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. 

The bis-arylammonium chlorides 24 and 25 emit excimer fluorescence in dilute aqueous solutions. No efiect of the addition of a- or P-CD was observed on the fluorescence of 24, whereas the addition of y-CD increased the intensity ratio of the excimer to monomer. The addition of P-CD to 25 caused the disappearance of the excimer while, after the addition of y-CD, the monomer peak almost disappeared. The authors proposed that the inclusion of only one aryl moiety inhibits the excimer formation, whereas the larger y-cavity can host two biphenyl groups, which facilitates excimer formation. According to the authors, formation of the eclipsed conformers of 24 and 25, which alone can give excimer, occurs in the excited state [138]. 

TABLE 4 Excimer to Monomer Emission Intensity Ratio for Dinaphthylpropanes in Water and in the Presence of 5 x 10 M CD ... 

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