Monomer emission ratio

Polymeric Systems.—Absorption, fluorescence excitation, and emission spectra of soluble poly(diacetylene) at room and liquid nitrogen temperature has been recorded for different solvents. The excimer-to-monomer emission ratio for polystyrene depends upon the polymer molecular weight but is independent of the solvent. Monolayer films of the 27-carbon-chain-length alkyldiace-... 

The interesting phenomenon where a mixture of two poor solvents or nonsolvents for a polymer provides a medium that acts as a good solvent for die polymers has been the objective of many studies, by light scattering, " viscometry, " sorption equilibrium, and fluorescence. From these techniques, it has been possible to appreciate how the second virial coefficient Aj and the intrinsic viscosity [11] preferential adsorption coefficient A, and excimer and monomer emission ratio Ie/Im are involved by changing solvent composition. They present ([T)], A2) a maximum or a variation at a certain solvent composition where the polymer behaves as through it were dissolved in a good solvent. 

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. 

The exciplex intensity showed quite different behavior as the setting proceeded. A comparison of the (monomer peak/monomer peak) ratio to the (exciplex peak/monomer peak) ratio was quite illuminating. We considered the initial maximum wavelength of the exciplex emission at 540 nm, and compared its intensity to the monomer intensity at 405 nm as the dissolution/ polymerization proceeded. A substantial decrease in exciplex intensity, compared to monomer intensity, was observed over the first 40 min of the cure. The ratio then leveled off, indicating that the local viscosity had reached a maximum after 40 min and that the dissolution/polymerization was considered to have reached completion at the ambient temperature of the laboratory. Since the working time for the cement was considerably less than the 40-min time period over which the exciplex/monomer intensity ratio was steadily decreasing, the intensity ratios served as in situ monitors of the cure. 

Fig. 46 Pyrene monomer and excimer decay profiles in SDS micellar solutions [SDS] = 8.2 X 10 kmolm , [NaCl] = 10 kmolm , CMC = 1.5 x 10" kmolm", pyrene levels are indicated as the ratio of micellized SDS to added pyrene emission monitored at 383 nm for monomer and 480 nm for excimer. (A) Monomer emission for SDS/Py = 2160, (B) monomer emission for SDS/Py 108 (C) excimer emission for SDS/Py = 108...

Fluorescence is measured in dilute solution of model compounds for polymers of 2,6-naphthalene dicarboxylic acid and eight different glycols. The ratio of excimer to monomer emission depends on the glycol used. Studies as functions of temperature and solvent show that, in contrast with the analogous polyesters in which the naphthalene moiety is replaced with a benzene ring, there can be a substantial dynamic component to the excimer emission. Extrapolation to media of infinite viscosity shows that in the absence of rotational isomerism during the lifetime of the singlet excited state, there is an odd-even effect In the series in which the flexible spacers differ in the number of methylene units, but not in the series in which the flexible spacers differ in the number of oxyethylene units. 

Figure 16 Emission spectra of PBAC (2.6 p,A/) at (A) low and (B) high concentrations of BAZrPAex = 340 nm. The inset shows the ratio of excimer to monomer emission as a function of phosphate concentration at 3.5 xA/ PBAC. (From Ref. 20. Copyright 1993 Elsevier Publications.)...

Fig. 6 Ratio of intramolecular excimer (/ ) and monomer (/) emission intensities (a) and energy of excimer emission (b), as function of n in a,co-di(l-pyrenyl) alkanes, Pyr-(CHa) -Pyr. (Reproduced with permission from Zacchariasse and Kuhnle, 1976)...

Fluorescent hydrophobes (naphthyl and pyrenyl groups) incorporated into the polysulfobetaines are a powerful tool for studying the formation of intra-and interpolymer aggregates in aqueous and aqueous salt solutions [85,229-231]. Intermacromolecular hydrophobic association is observed as an increase in the excimer emission relative to that of the monomer emission, where h/Iu is the ratio of intensities of excimer and monomer fluorescence which reflects the extent of inter/intra macromolecular interactions. Intramolecular micellization is easily monitored by the quenching efficiency of the thallium ions. The decrease of h/Iu reflects the breaking of the intra- and interchain associations in aqueous salt solutions, leading to chain expansion. 

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... 

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... 

Before we leave this section we should note that our explanation of the monomer emission as due to a special pre-formed shallow trap suggests that the low-temperature monomer/excimer emission intensity should be morphology dependent, hence dependent upon sample history, molecular weight, etc. This is indeed the case and we have found that different batches of polymer, aged samples, or samples prepared in different ways than described, may give slightly different intensity ratios at 20K. However, our results for samples prepared as described are completely reproducible and the temperature dependences remain qualitatively the same for deviant samples. 

The fluorescence spectra of poly(ACN-co-MAN) showed monomer emission at 346 nm and excimer emission at 405 nm. The intensity of the excimer emission band decreased as the percentage of ACN decreased from 14 to 5 and shifted to a longer wavelength at 412 nm. Corresponding Iq/Im ratios decreased from 0.33 ro 0.13, respectively. 

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). 

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