Pyrene spectra

Typical pyrene spectra in HMHEC/surfactant solutions are shown in Figure 7. Figure 8 gives values for the ratio I3/I., for aqueous SDS/polymer solutions containing pyrene as a function of SDS concentration. For SDS in water, I3/I.1 assumes two different values above and below the cmc, as expected. Below the cmc, the pyrene resides in the bulk (aqueous) solution, with I3/I.J = 0.68 (13/1 water = above the... 

Figure 1 Pyrene spectrum at 37.4 °C and 83.0 bars. The system concentration is y2 = 3.2 x 10-. The spectrum peaks Ii and I3 are labelled.

Medenwald suggests that the infrared spectrum of aminoaza-pyrene (238) favors the imino form. Di-(2-quinolyl) amine has been reported to exist in two modifications, one of which was the imino form 239, but this seems improbable. 

Figure 1. (a) Room-temperature fluorescence spectra of benzo(a)pyrene on 80% a-Room-temperature fluorescence spectrum of 500 ng of benzo(a)pyrene on 80% a-<7clodextrin—NaCl. = 300 nm. 

Figure 2. (a) Room-temperature phosphorescence spectrum of benzo(e)pyrene on 80% a-cyclodextrin-NaCl in the presence of ben2o(a)pyrene. = 284 nm. (h) Room-temperature phosphorescence spectrum of benzo(e)pyrene on 80% a-cyclodextrin—NaCl. X - 284 nm. 

Figure 3. Three-dimensional plot of the room-temperature fluorescence of a mixture of 500 ng each of benzo(a)pyrene and benzo(e)pyrene on 80% q-cyclodextrin-NaCl. Numbers along dashed lines show the approximate wavelengths (nm) represented by these lines. The excitation wavelength was varied from 250 nm (front spectrum) to 370 nm (back spectrum) at 2-nm increments. Benzo(a)pyrene emitted from approximately 380 nm to 540 nm, and benzo(e)pyrene emitted from 365 nm to 505 nm.

Pyrene is metabolized by the fungus Crinipellis stipitaria to 1-hydroxypyrene, and this has a spectrum of toxic effects substantially greater than those of pyrene these include cytotoxicity to HeLa S3 cells, toxicity to a number of bacteria and to the nematode Cae-norhabditis elegans (Lambert et al. 1995). 

Emission spectra at these points are shown in Figure 8.2d. The band shapes were independent of the excitation intensity from 0.1 to 2.0 nJ pulse . The spectrum of the anthracene crystal with vibronic structures is ascribed to the fluorescence originating from the free exdton in the crystalline phase [1, 2], while the broad emission spectra of the pyrene microcrystal centered at 470 nm and that of the perylene microcrystal centered at 605 nm are, respectively, ascribed to the self-trapped exciton in the crystalline phase of pyrene and that of the a-type perylene crystal. These spectra clearly show that the femtosecond NIR pulse can produce excited singlet states in these microcrystals. 

Figure 7.4 shows the absorption spectrum of pyrene, evaluated with Equation 7.8 (above), and the Kubelka-Munk spectrum of pyrene (below), evaluated by use of Equation 7.7. 

Additional support for this disassembly mechanism was obtained by monitoring the release of the pyrene tail units by fluorescence spectroscopy. The confined proximity of the pyrene units in the dendritic molecule results in formation of excimers. The excimer fluorescence generates a broad band at a wavelength of 470 nm in the emission spectrum of dendron 31 (Fig. 5.25). Upon the release of the pyrene units from the dendritic platform, the 470 nm band disappeared from... 

Different aromatic hydrocarbons (naphthalene, pyrene and some others) can form excimers, and these reactions are accompanying by an appearance of the second emission band shifted to the red-edge of the spectrum. Pyrene in cyclohexane (CH) at small concentrations 10-5-10-4 M has structured vibronic emission band near 430 nm. With the growth of concentration, the second smooth fluorescence band appears near 480 nm, and the intensity of this band increases with the pyrene concentration. At high pyrene concentration of 10 2 M, this band belonging to excimers dominates in the spectrum. After the act of emission, excimers disintegrate into two molecules as the ground state of such complex is unstable. 

The pyrene-like aromatic chromophore of BaPDE is characterized by a prominent and characteristic absorption spectrum in the A 310-360 nm spectral region, and a fluorescence emission in the X 370-460 nm range. These properties are sensitive to the local microenvironment of the pyrenyl chromophore, and spectroscopic techniques are thus useful in studies of the structures of the DNA adducts and in monitoring the reaction pathways of BaPDE and its hydrolysis products in DNA solutions. 

Site I is characterized by a relatively large red shift of 10 nm in the absorption maxima (relative to the aqueous solution spectra), exhibiting maxima at 337 and 354 nm, and a negative AA spectrum all of these properties are consistent with an intercalation-complex geometry in which the planar pyrene ring-system is nearly parallel to the planes of the DNA bases. 

Site II is characterized by a relatively small 2-3 nm red shift in the absorption spectrum and a positive AA spectrum. In this conformation, the planes of the pyrene moeities tend to align parallel rather than perpendicular to the axis of the DNA helix. 

Figure 7. Absorption spectra in 15% methanol at 23°C of trans-7,8-dihydroxy-7,8-dihydrobenzo[5]pyrene in native DNA at concentrations of 0.0, 8.0 x l0 5, 1.6 x 10 2.4 x 10, 3.2 x 10 and 4.0 x 10 M. The broken line shows a spectrum in the presence of 3.2 x 10 M DNA and 3.2 x 10 M spermine. (Reproduced with permission from Ref. 15. Copyright 1985, Alan R. Liss.)...

Since the same dye molecules can serve as both donors and acceptors and the transfer efficiency depends on the spectral overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor, this efficiency also depends on the Stokes shift [53]. Involvement of these effects depends strongly on the properties of the dye. Fluoresceins and rhodamines exhibit high homo-FRET efficiency and self-quenching pyrene and perylene derivatives, high homo-FRET but little self-quenching and luminescent metal complexes may not exhibit homo-FRET at all because of their very strong Stokes shifts. 

A first generation poly(amido amine) dendrimer has been functionalized with three calyx[4]arenes, each carrying a pyrene fluorophore (4) [30]. In acetonitrile solution the emission spectrum shows both the monomer and the excimer emission band, typical of the pyrene chromophore. Upon addition of Al3+ as perchlorate salt, a decrease in the excimer emission and a consequent revival of the monomer emission is observed. This can be interpreted as a change in the dendrimer structure and flexibility upon metal ion complexation that inhibits close proximity of pyrenyl units, thus decreasing the excimer formation probability. 1H NMR studies of dendrimer 4 revealed marked differences upon Al3+ addition only in the chemical shifts of the CH2 protons linked to the central amine group, demonstrating that the metal ion is coordinated by the dendrimer core. MALDI-TOF experiments gave evidence of a 1 1 complex. Similar results have been obtained for In3+, while other cations such as Ag+, Cd2+, and Zn2+ do not affect the luminescence properties of... 

The width of a band in the absorption or emission spectrum of a fluorophore located in a particular microenvironment is a result of two effects homogeneous and inhomogeneous broadening. Homogeneous broadening is due to the existence of a continuous set of vibrational sublevels in each electronic state. Absorption and emission spectra of moderately large and rigid fluorophores in solution could therefore be almost structureless at room temperature. However, in some cases, many of the vibrational modes are not active, neither in absorption nor in emission, so that a dear vibrational structure is observed (e.g. naphthalene, pyrene). 

The relative changes in intensity of the vibronic bands in the pyrene fluorescence spectrum has its origin in the extent of vibronic coupling between the weakly allowed first excited state and the strongly allowed second excited state. Dipole-induced dipole interactions between the solvent and pyrene play a major role. The polarity of the solvent determines the extent to which an induced dipole moment is formed by vibrational distortions of the nuclear coordinates of pyrene (Karpovich and Blanchard, 1995). 

Tab. 7.4. Solvent dependence of the ratio / //m of the fluorescence intensities of the first and third vibronic bands in the fluorescence spectrum of pyrene.

The Na+ sensor M-9 has a structure analogous to that of compound E-4, but instead of two identical pyrene fluorophores, it contains two different fluorophores with a pyrene group and an anthroyloxy group. Resonance energy transfer (see Chapter 9) from the former to the latter is then possible because of the spectral overlap between the fluorescence spectrum of the pyrene moiety and the absorption spectrum of the anthroyloxy moiety. Upon addition of Na+ to a solution of M-9 in a mixture of MeOH and THF (15 1 v/v), the fluorescence of the anthroyloxy group increases significantly compared with that of the pyrene group, which permits a ratiometric measurement. 

Figure 8.2 presents the fluorescence of pyrene on silica gel. The loading is low so that pyrene is predominantly adsorbed as nonaggregated monomers (Mi). The backward fluorescence spectrum Fb of this sample is very comparable to the spectrum in polar solvents and not distorted by reabsorption. However, the forward spectrum Ft is almost completely suppressed in the region of overlap with the o -transition and hot sidebands of the weak first absorption band Si. The absorption coefficients of the sample vary widely from k" = 0.1 cm 1 (Si-band, Aa = 350-370 nm) to k = 25 cm-1 (S2-band, 1 290-340 nm), and in a first approximation the excitation spectrum of Fh reflects this variation correctly (Figure 8.2, left). The Ff-excitation spectrum, however, has only little in common with the real absorption spectrum of the sample. 

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