Pyrene monomer emission intensity

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... 

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...

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. 

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). 

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... 

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.

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...

Figure 7.32 Kinetics of luminescence of pyrene following laser flash excitation. L, laser pulse profile M, monomer emission, E, excimer emission rise and decay. Horizontal axis, time in ns vertical axis, light intensity in arbitrary units. The three kinetic curves are normalized to a common maximum...

Following this same approach, Jin and coworkers have prepared a nearly identical pyrene-modified calixarene, 38, where the methoxy groups are replaced by ester functionalities [377], Na+ and K+ ions perturb the relative intensities of excimer and monomer emission in much the same manner as 37. Unlike 37, however, 38 is not sensitive to Li+ ion. 

It is concluded that below the transition temperature the monomer intensity increases with increasing temperature due to excimer dissociation to excited-state monomer. Above the transition temperature the excited-state equilibrium is apparently broken because the thermal energy is sufficient to activate excimer non-radiative decay by dissociation to ground-state monomer. Consequently, the monomer emission no longer increases with increasing temperature and the isobestic point disappears. Pyrene has been used as a fluorescent probe to monitor the conformational state of maleic acid with... 

Excimer fluorescence of pyrene attached to synthetic polymer chains can be used to study polymer conformation in solution and on particle surfaces. In this case, fluorescence spectroscopy involves the measurement of the emission intensity of monomer (/ , observed at 375 mn) and excimer (/ at 480 nm). The ratio of f to I is related to coiling/stretching behavior of a labeled polymer and we have called it the coiling index. In the absence of intermolecular interactions (the polymer concentration used is usually below this limit), a high value of IJI can be considered the result of a coiled conformation whereas a low value is associated with a stretched conformation. 

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. 

Fig. 1.26 The effect of concentration on the emission spectrum of pyrene in air-equilibrated ethanol for 2exc = 330 nm. The spectra are normalised to the 372 nm peak and the concentrations are (1) lx 10 mol dm (2) 1 x 10 " mol dm (3) 1 x 10 mol dm . In dilute solution, a structured emission band between 350 and 450 nm is observed, which is assigned to the pyrene monomer. As the pyrene concentration is increased, a broad emission band between 425 and 550 nm emerges, which is attributed to emission from the pyrene excimer. The monomer to excimer ratio is dependent on both pyrene concentration and the excited state lifetime, which is reduced here due to oxygen quenching. Degassing of the solution to remove oxygen would result in an increase in the relative intensity of the excimer emission band...

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