Monomer emission intensities

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. 

Lariat crown ethers with two terminal pyrenyl sidearms connected to the same carbon 103 (/= 0, 1 m = 0-2 n = 0-2) or to two different carbon atoms 104 (m = 0-2 n 1,2) and 105 (m 0, 1) showed intramolecular excimer emission in the free state (Jt-Jt-stacking of the pyrene rings), whose intensity decreases with the increase of monomer emission intensity upon metal ion complexation <20020L2641, 2004JOC4403>. This response has been ascribed to the cooperative participation of one of the two sidearms in the complexation of the crown ring with the metal ion, which renders inoperative the Jt-Jt-stacking of aromatic rings. Most of these fluorophores show alkaline earth over alkali metal ion selectivities. 

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)...

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... 

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

The essential feature of the intramolecular cyclization of short polymer chains containing terminal pyrene groups is that the process is difiiision controlled at room temperature. As such, the cyclization process is expected to obey an Einstein relation with both the rate constant for cyclization and the ratio of excimer to monomer emission intensities proportional to... 

To explore this analogy, we will review previous work on the influence of stoichiometry as well as present new results on the effect of neutralization on macromolecular complex formation. In addition, we will review very recent results for adsorption on colloidal silica and present preliminary results for the adsorption on colloidal polystyrene. The excimer to monomer emission intensity ratio, the excitation spectra, and the lifetimes of the excimer and monomer are the observable experimental parameters. 

Figure 1. Intramolecular excimer to monomer emission intensity ratio as a function of the molar ratio of poly carboxylic acid) to PEG for Py-PEG-Py of weight-average molecular weights 4800 and 9200. All data are nomwlized by the Id/Im value for a 1% pyrene-tagged PEG solution with no polyacid added.

The experimental quantity easiest to observe in a photophysical experiment such as the ones described herein is l l uy the ratio of excimer to monomer emission intensities. Interpretation of the results is not completely straightforward, however. Winnik (28) has shown that IdUm for the end-labeled polymers in dilute solution is proportional to the rate constant for cyclization as such, it may be interpreted in terms of the influence of molecular weight and solvent quality on the configurational statistics of the chain. 

Pyrene Monomer and Excimer Emission. The emission of locally isolated excited pyrenes ( monomer emission, intensity Im) is characterized by a well-resolved spectrum with the [0, 0] band at 378 nm. The emission of pyrene excimers (intensity Ie), centered at 480 nm, is broad and featureless. Excimer formation requires that an excited pyrene (Py ) and a pyrene in its ground state come into close proximity within the Py lifetime. The process is predominant in concentrated pyrene solutions or under circumstances where microdomains of high local pyrene concentration form, even though the total pyrene concentration is very low. This effect is shown for example by... 

Monomer emission intensity determined at 415nm for and at 376nm for Measurements in THE at room temperature under nitrogen atmosphere. The intensity ratio was extrapolated to infinite dilution. 

Early investigations were concerned primarily with considerations of the thermodynamic characteristics of the interaction through a study of the temperature and solvent dependence of the excimer to monomer emission intensity ratio. In addition, some kinetic information was... 

The lifetime of many aromatic fluorophores is of the order of 10 s, similar to the relaxation times for conformational transitions in paraffinic chains. Thus, the ratio of excimer and monomer" emission intensities can be used to estimate the rate constant for the hindered rotation required to form the excimer conformation in a molecule containing two aromatic residues. A detailed study based on this principle has been carried out in De Schryver s laboratory and is reported elsewhere in this volume. 

Numerous studies of the photophysics of aryl vinyl polymers have shown that the monomer emission intensity can be empirically fit to a triple exponential [15-17]. The immediate conclusion that may be drawn from this observation is that the Birks kinetic scheme [1], which was developed for a collision-induced intermolecular process between small molecules in solution, is inapplicable to intramolecular excimer formation in macromolecules. 

Fig. 2.4. Pyrene monomer emission intensity (I as s function of temperature for a solution of HPC-Py/56 in water (0.12 g/1) and average turbidity for a solution of HPC-Py/56 in water (0.40 g/1) as a function of temperature...

Fig. 6.33 Intramembrane lipid recognition. Left Temperature dependence of pyrene PC excimer/ monomer emission intensity in suspensions of CA-PE (dark gray), M-PE (light gray), POPC (black), and a 1 1 mixture of CA-PE and M-PE (black). Right DSC upscan (-) and downscan (—) traces of a suspension of a 1 1 mixture of CA-PE and M-PE CA-PE and M-PE upscans (-, ) and downscans (-, —) are all flat traces. Reprinted with the permission from Ref. [62]. Copyright 2008 American Chemical Society...

Yana et al. [27] prepared an a-helix peptide system 20 composed of 17 amino acids with two naphthalene units at the same side of fi-CT) in the peptide side chain (Fig. 8). This system was designed to signal the detection of a guest by an increase in the excimer emission intensity. 20 by itself exhibits strong monomer emission around 336 nm and relatively weak excimer emission around 390 nm. The excimer is formed between the two intramolecular naphthalene units outside the CD cavity. Upon addition of UDCA, the monomer emission intensity... 

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