Pyrene units

Thomas et al. [64] prepared copolymers of 1-pyreneacrylic acid with acrylic acid (AA), 17, and with methacrylic acid (MA), 18, incorporating not more than one pyrene unit per polymer chain. The mole ratios of pyrene to AA and MA units were 1150 and 1390, respectively. The molecular weights of 17 and 18 were 8.3 x lO4... 

The optical absorption spectra and the first reduction potentials are virtually independent of the number of pyrene units present in the molecule, as a result of the specific stereoelectronic situation. Since the orbital coefficients of the bridgehead centers are almost zero, the rings are electronically decoupled. Thus, oligopyrenes differ significantly from oligo(pflrfl-phenylene)s (OPVs). 

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... 

E-3 (Figure 10.26) is the first example of an ionophoric calixarene with appended fluorophores, demonstrating the interest in this new class of fluorescent sensors. The lower rim contains two pyrene units that can form excimers in the absence of cation. Addition of alkali metal ions affects the monomer versus excimer emission. According to the same principle, E-4 was designed for the recognition of Na+ the Na+/K+ selectivity, as measured by the ratio of stability constants of the complexes, was indeed found to be 154, while the affinity for Li+ was too low to be determined. 

Similarly, the fluorescence intensity of the 1,4-disubstituted azine with ferrocene and pyrene units (17) can be reversibly modulated by sequential redox reactions of ferrocene moiety. In the neutral state, compound 17 displays weak fluorescence owing to the electron transfer from the ferrocenyl group to the excited pyrene unit or by energy transfer from the excited pyrene unit to the ferrocenyl unit. Oxidation of the ferrocenyl unit, however, leads to remarkable fluorescence enhancement. This is because the ferrocenium cation shows weak electron donating ability and also the corresponding spectral overlap becomes small.27... 

Figure 6 Fullerene derivative with pyrene unit as addent. (From Ref. 75.)...

Shinkai and coworkers have capitalized on this conformation flexibility in their designs of several pyrene-derivatized calixarene chemosensors. The rotated phenyl ring of the partial cone conformer of 37 allows two pyrene units to more easily interact by decreasing steric hindrance at the lower rim [376], Addition of Li+, Na+, and K+ ions enforces cone formation and the disruption of the initially formed excimer. Accordingly, the metal ions are detected by a decrease in pyrene excimer emission and concomitant increase in the pyrene fluorescence. 

The co-operative structural fluctuation in self-assembled monolayers is also considered to be dominated by the n-n interaction between the pyrene units. The 7i-7i interaction involves a move of electronic charge between molecules, often leading to the formation of intermolecular donor-acceptor complexes. This kind of interaction can also affect the structure of self-assembled monolayers [36]. 

Related optical and fluorescent sensor systems have been widely used. For instance, the fluorescence of the pyrene unit in species (187) is quenched upon saccharide binding to the boron center. Boronic acid groups were also attached to dendrimers and polymers. The benefit of systems containing at least two boronic acid centers, as shown for the luminescent saccharide sensor (187), is that two-point binding can more effectively control saccharide binding. Similar... 

Analysis of the data showed the presence of a fast intramolecular photoinduced energy transfer process from pyrene -perylene to pyrene-perylene (ken 6.2 x 109 s 1) with a high yield (>90%), followed by efficient intramolecular electron transfer from pyrene-perylene to pyrene +-perylene (70%, ket 6.6 x 109s 1). Both processes occur from the pyrene unit to the perylene moiety. The Forster distance was calculated to be 3.4 nm and the corresponding donor-acceptor distance was calculated from the energy transfer rate as 0.9 nm. No indications for energy hopping between different pyrene moieties were observed. 

Amodel experiment is shown here to clarify the stiffness of the fluorocarbon chains [2 ]. Diester 1 with two pyrene units shows an additional broad fluorescence, characteristic of the intramolecular pyrene excimer (425-600 nm)(Chart A). Meanwhile, diester 2 with two pyrene units separated with a QF 7 segment and 3 and 4 with one pyrene unit show only a weak emission in the region of 425-600 nm (Chart B). Since the excimer arises from the intramolecular interaction of two pyrene units, no excimer from 2 indicates that there exists no intramolecular interaction between pyrene emits in 2, demonstrating that the stiffness of the fluorocarbon chains does not allow the intramolecular interaction. 

Figure 3.27 Belt-shaped aromatic compounds are equivalent to carbon nanotubes of minimal length, (a) The shortest possible zig-zag nanotube, and (b) hypothetical armchair nanotubes made of pyrene units.

Taking this approach a step further, the same group developed a system that used Tt—n interactions as well as hydrogen bonds, in which the pyrene units were attached at the ends of a polybutadiene polymer that was functionalized with urethane groups. The blend showed an increased tensile modulus compared to... 

Pyrene, a fluorophore that displays excimcT emissimi specifically at higher density/concentration was choscai for highlighting the fidelity of surface functionalization. The UV—visible absorbance of the pyrene chromophme capping the nanoparticle was used to determine the amount of pyrene units present on the surface of silica nanoparticles... 

Figure 3 (a) Structure of Flavin Flox and Fhad (b) AnNPs functionalized with diacyldiaminopyridine hydrogen-bonding moieties and pyrene units to enhance flavin recognition through arene- 7r stacking perform better than (c) mono-receptor-functionalized AuNPs lacking the pyrene support. ... 

The disruption of a dimeric form of cyclodextrins containing an appended pyrene unit (Fig. 14a) as a result of the inclusion of a guest compound was the rationale of the observed quenching of the pyrene excimer band observed by Ueno and coworkers [122]. Small differences in the inclusion of the two fenchone enantiomers (+)- and (—)-46 were reported. 

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