Pyrene emission intensity

Figure 4.13 Plot of pyrene emission intensity as a function of temperature for aqueous solution of poly-(N-isopropylacrylamide) (PNIPAM) labelled with naphthalene(N)-donor and pyrene(Py)-acceptor PNIPAM-Py/366-N/50, 44 ppm in water. Wavelength excitation at 290 nm due to N excitation, at 328 nm due to...

FIGURE 13.22 Plots of the uorescence inteniiftsnd intensity rati ofei /13 (from pyrene emission spectra) andl333/l338 as a function of PSTj-poly(sodium acrylate) concentration. Values of C are indicated by arrows. (Reproduced from Asta eva, I., X. Zhong, and F. A. Eisenberg. Maa >molecule 6 7339-7352. With permission from American Chemical Society.)... 

Enhanced excimer emission was also observed from PBAC bound to a-ZrP [20], Excimer formation from pyrene is well known in aqueous solutions [54], As in the case with AMAC, excimer formation is increased with PBAC concentration (Fig. 16) due to increased local concentrations but with two significant differences. Hydrophobic interactions between the pyrene molecules favor the aggregation of PBAC even at moderate coverages and the PBAC singlet excited state is much longer lived ( 200 nsec) than that of AMAC ( 10 nsec) these factors, in turn, promote excimer formation even at low loadings. The broad, red-shifted fluorescence band with a peak centered around 470 nm, characteristic of the pyrene excimer emission, is evident in Fig. 16. Rapid formation of the excimer at low coverages is also evident from the plot of the ratio of emission intensities at... 

A Cu(II)-induced perturbation of pyrene fluorescence has been utilized to create a sensor for glutamate [388], A 2 2 1 Cu2+ 3-CD pyrene complex is formed by the noncovalent assembly of the constituents the site of Cu(II) binding is unknown. The pyrene emission resulting from complexation of the lu-mophore to 3-CD is effectively quenched by the addition of Cu(II). A 500-fold enhancement in pyrene intensity is observed upon the addition of 1.87 M glutamate, which is presumed to extract Cu(II) from the 2 2 1 complex. The precise nature of the quenching and restoration mechanisms is currently unknown. 

Pyrene is one of the most widely studied neutral fluorescence probes, and accordingly, this was sometimes used to determine the polarity of some ILs. The polarity scale of the IL analyzed with pyrene is defined as the emission intensity... 

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. 

Solvatochromic fluorescent probe molecules have also been used to establish solvent polarity scales. The solvent-dependent fluorescence maximum of 4-amino-V-methylphthalimide was used by Zelinskii et al. to establish a universal scale for the effect of solvents on the electronic spectra of organic compounds [80, 213], More recently, a comprehensive Py scale of solvent polarity including 95 solvents has been proposed by Winnik et al. [222]. This is based on the relative band intensities of the vibronic bands I and III of the % - n emission spectrum of monomeric pyrene cf. Section 6.2.4. A significant enhancement is observed in the 0 0 vibronic band intensity h relative to the 0 2 vibronic band intensity /m with increasing solvent polarity. The ratio of emission intensities for bands I and III serves as an empirical measure of solvent polarity Py = /i/Zm [222]. However, there seems to be some difficulty in determining precise Py values, as shown by the varying Py values from different laboratories the reasons for these deviations have been investigated [223]. 

Fig. 10.3 (a) Direct titration of a fluorescent RNP complex (0.1 pM) of the A28 RNA subunit and a Rev peptide modified with pyrene at the amino terminal (Pyr-Rev) with ATP (1,3, 10, 30, 100, 300, 1,000, and 3,000 iM) shows an increase in fluorescence intensity. A spectrum in the absence of ATP is shown in bold line, (b) A saturation curve for the fluorescence emission intensity of A28/Pyr-Rev to ATP (open circles), UTP (filled squares), CTP (filled triangles), or GTP (filled circles) indicates A28/Pyr-Rev responds selectively to the addition of ATP... 

Pyrene is extremely sensitive to the polarity of the microenvironment surrounding it. As the polarity of the microenvironment increases, the emission intensity of the first vibronic band (/,) increases, while the emission intensity of the third vibronic band (I3) decreases. Thus, ///. is related to the dipolarity of the microenvironment surrounding the pyrene molecules for example /,//3 shifts from 0.58 in cyclohexane to 1.87 in water.72 73 PRODAN and DCM are solvatochromic fluorophores whose fluorescence band position is extremely sensitive to the polarity of the surrounding microenvironment. For example, the fluorescence emission maximum of PRODAN shifts from 401 nm in cyclohexane to 531 nm in water.74-75... 

Pyrene has been used widely as a photophysical probe because of its long fluorescence lifetime and great tendency for excimer formation. Emission characteristics of pyrene molecules depend on the nature of the solvent. The ratio of relative intensities of the 1st (373 nm) and lllrd (383 nm) peaks, Ijjj/Ij, in a pyrene emission spectrum decreases as the polarity of the solvent increases. This... 

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. 

Figure 2.9 Delayed luminescence (solid line) from a solution of 1 x10-5m pyrene in methylcyclohexane at 193 K and absorption spectrum (dotted line). Note the logarithmic scale covering eight orders of magnitude in emission intensity. Reproduced from ref. 39 with permission. Copyright 1967, American Institute of Physics...

Even in the case of simple aromatic dopants (naphthalene, anthracene, pyrene), fluorescence intensity is found to decrease with successive laser pulses and/or increasing laser fluence. The decrease may be ascribed to thermal desorption of the dopant, as indicated by Fukumura et al. [62], and/or to photooxidation/degradation of the dopants. In the present case, film transmission decreases in parallel with the dopant fluorescence, thus indicating the formation of photoproducts that absorb stronger than the precursor. (The photoproduct(s) are not detected in the fluorescence experiments, evidently because of its (their) low emission yield). NapH and related compounds are known to generate (Ag) efficiently [81]. This has a long lifetime within polymers and it can attack the aromatic to form the corresponding endoperoxide (Nap-02). Such processes have been shown to occur in related polymer systems. 

Fig. 86 Fluorescence spectra of a pyrene-implanted PBMA surface as a function of laser pulse number. Pyrene was transferred using ablation of a triazene polymer. Laser flu-ence 100 mj creT2, (a) 5 pulses, (b) 10 pulses, (c) 15 pulses, (d) 20 pulses. The vibrational pyrene emission peaks are denoted (I-V). Inset Normalized fluorescence intensity of the V pyrene peak at 393 nm vs laser pulse number. Data are taken from the spectra in the main figure. REPRINTED WITH PERMISSION OF [Ref. 360], COPYRIGHT (1998) Elsevier Science...

J2.4 Nonradiative Energy Transfer Unique information concerning the conformational behavior of aqueous solutions of PAA bearing naphthyl (donor) and pyrenyl (acceptor) species has been derived from NRET measurements [120]. A plot of the ratio of pyrene to naphthalene emission intensity (/py//np) upon excitation of the naphthalene fluorophores at 290 nm as a function of pH is shown in Fig. 2.10. The... 

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.

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