Fluorescence monomer

Fluorescence Rise and Decay Curves. Both monomer and excimer fluorescence decay curves of the unirradiated film are nonexponential and the excimer fluorescence shows a slow rise component. This behavior is quite similar to the result reported for the PMMA film doped with pyrene. (23) A delay in the excimer formation process was interpreted as the time taken for the two molecules in the ground state dimer to form the excimer geometry. Dynamic data of the ablated area observed at 375 no (monomer fluorescence) and 500 nm (exciner fluorescence) are shown in Figure 5. When the laser fluence increased, the monomer fluorescence decay became slower. The slow rise of the excimer fluorescence disappeared and the decay became faster. 

Fluorescence Instrumentation and Measurements. Fluorescence spectra of the FS samples were obtained on a steady state spectrofluorometer of modular construction with a 1000 W xenon arc lamp and tandem quarter meter excitation monochromator and quarter meter analysis monochromator. The diffraction gratings In the excitation monochromators have blaze angles that allow maximum light transmission at a wavelength of 240 nm. Uncorrected spectra were taken under front-face Illumination with exciting light at 260 nm. Monomer fluorescence was measured at 280 nm and exclmer fluorescence was measured at 330 nm, where there Is no overlap of exclmer and monomer bands. 

Fluorescence spectra of the novolac samples were measured on a Spex Fluorolog 212 spectrofluorometer with a 450 W xenon arc lamp and a Spex DM1B data station. Spectra were taken with front-face Illumination using a 343 or 348 nm excitation wavelength for solutions or films, respectively, which are near the maximum transmission region of this spectrometer. Spectra were corrected using a rhodamlne B reference. Monomer fluorescence was measured at 374 or 378 nm and exclmer fluorescence was measured at 470 nm. Monomer and exclmer peak heights were used In calculations of Ie/Im. The 1 monomer peak of pyrene was used to reduce overlap with the exclmer emission. 

Kalyanasundaran K. and Thomas J. K. (1977b) Environmental Effects on Vibronic Band Intensities in Pyrene Monomer Fluorescence and their Application in Studies of Micellar Systems, J. Am. Chem. Soc. 99, 2039-2044. 

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. 

Phase-separation immunoassays have been reported, in which the solid phase particles are formed after the immunoreaction is completed.(42) Phase-separation immunoassays are advantageous since the unstirred layer of solution near a solid surface alters diffusion and binding kinetics at the surface in comparison with the properties of the bulk solution. In phase-separation assays for IgG and IgM, capture antibodies are bound with monomers suitable for styrene or acrylamide polymerization.(42) Monomer-labeled capture antibodies are reacted with analyte and with fluorescein- and/or phycoerythrin-labeled antibodies in a sandwich assay, followed by polymerization of the monomers. Fluorescence of the resulting particles is quantitated in a FACS IV flow microfluorometer, and is directly proportional to analyte concentration. 

Fig. 38 Adsorption isotherm of TTAC at alumina-water interface at pH 10, ionic strength 0.03 M NaCl and corresponding changes in pyrene monomer fluorescence from the alumina-water interface and the supernatant...

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. 

Baker and coworkers [16] reported on a self-referencing luminescent thermometer designed around the temperature-dependent intramolecular excimer formation/dissociation of the molecular probe l,3-Ws(l-pyrenyl)pro-pane (BPP) dissolved in 1-butyl-l-methylpyrrolidinium bjs(trifluoromethyl-sulfonyl)imide, [C4Cipyr][Tf2N]. Upon an increase in temperature, and hence a decrease in the IL s bulk viscosity, the excimer-to-monomer fluorescence... 

Excimers have been suggested in several other photochemical processes. The triplet lifetime of o-xylene decreases from 900 nsec at 0.01 M in methylcyclohexane to 13 nsec in 8M solution.50 The inefficiency of the triplet sensitized dimerization of indene has been attributed to formation of an indene excimer.51 The emission from acetone originally52 believed to arise from an excimer has now been shown53 to be the true monomer fluorescence while that attributed to the monomer appears to have been due to an impurity. 

When pyrene was adsorbed onto silica gel from cyclohexane solution, the prominant excimer fluorescence band at 4650 A was no longer observed, but the monomer fluorescence band at 3900 A remained little changed.9 This inhibition of the excimer fluorescence indicates that the molecules are so strongly bound to the substrate surface that they become immobilized, thus preventing the conjugate n system overlap required to produce excimer emission. 

CMS and Polystyrene Solutions in Cyclohexane. Both monomer and excimer fluorescences were observed in the pulse radiolysis of polystyrene solution in cyclohexane. The decay curves of monomer and excimer fluorescences at 287 and 360 nm are shown in Figures 7(a) and (b), respectively. Energy migration on the polymer chain has been discussed elsewhere (15). The dependences of the decay of monomer fluorescence and the rise of excimer fluorescence on the... 

Concentration of pyrene, c Fraction of light absorbed Relative intensity of monomer fluorescence Fluorescence yield of monomer, M K = (0M°/0M — l)/c... 

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. 

Emission from M, monomer fluorescence, is the topic of this section. The following questions will be considered ... 

How is the monomer fluorescence of aryl vinyl polymers or intramolecular excimer-forming compounds distinguished from that of monochromophoric compounds ... 

The lifetime of monomer fluorescence in the absence of routes to excimer formation is tm = (kFM + koM + kTM) 1 = ky1, and the intrinsic quantum yield is Qm = kpM/kM. The lifetime and intrinsic quantum yield of excimer fluorescence, td and Qd, will be considered in a later section. 

In all the above studies 4-9-37 41> the 1,3-diarylpropanes had a reduced monomer quantum yield due to substantial intramolecular excimer formation, but the monomer fluorescence spectrum was unchanged from that of the analogous monochromophoric... 

A similar but smaller intramolecular quenching effect was seen by Phillips and co-workers 44,4S) for 1-vinylnaphthalene copolymers incapable of excimer fluorescence. The monomer fluorescence lifetime of the 1-naphthyl group in the methyl methacrylate copolymer 44) was 20% less than the lifetime of 1-methylnaphthalene in the same solvent, tetrahydrofuran. However, no difference in lifetimes was observed between the 1-vinylnaphthalene/methyl acrylate copolymer 45) and 1-methylnaphthalene. To summarize, the nonradiative decay rate of excited singlet monomer in polymers, koM + k1M, may not be identical to that of a monochromophoric model compound, especially when the polymer contains quenching moieties and the solvent is fluid enough to allow rapid intramolecular quenching to occur. 

The only head-to-head polymer which has been examined for excimer fluorescence is polystyrene 25). Unfortunately, the synthetic route to this polymer leaves a number of stilbene-based structures in the sample, which have a lower-energy singlet state than either PS monomer (285 nm) or excimer (330 nm). Thus, fluorescence from these intrinsic stilbene traps was seen in the spectra of head-to-head PS in pure films and, to a lesser extent, in fluid solution. In the latter, the fluorescence of PS monomer was predominant, and the small amount of stilbene fluorescence was increased when a nonsolvent (methanol or cyclohexane) was added to the 2-methyl-tetrahydrofuran solution. In films of the polymer, stilbene fluorescence was the major spectral band, although some PS excimer fluorescence was also present in the spectrum. No monomer fluorescence at 285 nm was detected from films. Given the impure nature of the head-to-head PS sample, no conclusions on excimer formation in these systems could be drawn. 

In order to determine whether energy migration makes a significant contribution to the photophysical behavior of P2VN and PS in dilute miscible blends, it is instructive to calculate the expected exdmer-to-monomer fluorescence quantum yield ratio in the absence of energy migration. To do so, it is first necessary to assume that intermolecular and non-adjacent intramolecular EFS are absent. In addition, the adjacent intramolecular EFS are assumed to be frozen into the aryl vinyl polymer and must be excited by direct absorption of a photon. Since the absorption spectrum of an EFS is no different from that of non-EFS chromophores, then the calculated fraction of rings within EFS is sufficient to determine the fluorescence ratio. 

For systems in which the triplet state decays quickly and radiationlessly to ground, the excimer-to-monomer fluorescence quantum yield ratio is given by... 

Despite these difficulties, the depolarization of monomer fluorescence of copolymers of styrene 32 179, 1-vinylnaphthalene 32,179 183,18S,> and 2-vinylnaphthalene i79) has been studied in low-temperature solvent glasses. The same experiments were performed on PS 32,186) and PIVN 32, i86). Monomer fluorescence depolarization from room-temperature films of styrene i87) and 1-vinylnaphthalene 187) copolymers, and from blends of P(1 VN-co-MMA) with PMMA 179), has also been recorded. Finally, exci-mer fluorescence depolarization from room-temperature films of PS 188,189) and P(alpha-methyl S) 189) has been studied. 

Fluorescence quenching of PS 17,161,190,191), P2VN 157,192 194-> poly(l-naphthyl methacrylate) 149,199, poly(2-naphthylmethyl methacrylate 1SS>, P(S-co-MMA)161), and P(2VN-co-S)194) in solution has been examined. In all cases except one for PS 161, plots of IDi0/Id versus [Q] showed upward curvature similar to Eq. (7). Excimer fluorescence was quenched more rapidly than monomer fluorescence with increasing [Q]. In addition, the observed quenching of the fluorescence ratio and of the monomer fluorescence was roughly linear in [Q]. 

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