Pyrene chemical shifts

Hydroxypropiophenones, synthesis of 645 Hydroxypyrenes—see also 8-Hydroxy-l, 3,6-tris(iV,iV-dimethylsulfonamido)pyrene chemical shifts for 338... 

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... 

Fig. 16.13. Structures and C chemical shifts of some aromatic compounds (a) perylene (b) pyrene (c) anthracene and (d) 9,10-dihydroanthracene.

Boekelheide and his coworkers 235,236) have now reported data for the parent hydrocarbon, trans-15,16-dihydropyrene, 83. As expected, the bridge protons are very strongly shielded. They have also prepared a monoaza analogue, trans-1,3,15,16-tetramethyl-15,16-dihydro-2-aza-pyrene, 84, the chemical shifts of the internal methyl groups of which indicate a slight attenuation of the ring current 237>. 

The high field shift of the pyrene units protons (<5 = 0.64—2.61 ppm, for both 46b and 47b) is direct evidence for the anti-aromaticity of the species. Another strong indication of the anti-aromaticity of these dianions comes from the chemical shift of the tether hydrogens, which function as probes for the anisotropy effect in the system. The best example comes from the geminal hydrogens H14 and H14 in 46b/2K+, which appear at b = 9.93 and 3.22 ppm, respectively. 

The use of a probe molecule to study the properties of micellar medium requires the knowledge of the micellar binding site of the probe molecule, with absolute certainty under a specific condition, which is almost impossible to achieve by any experimental or theoretical technique. Pyrene, a highly hydrophobic water insoluble hydrocarbon molecule, has been used to determine the polarity of micellar medium, but its precise micellar binding site is not known with absolute certainty. For instance, pulsed Fourier transform NMR and chemical shift analyses used to determine the dynamic solubilization site of the pyrene in cationic micellar solutions show that pyrene is solubilized in the interior of the... 

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