Pyrene-containing molecules

Cascade Blue cadaverine and Cascade Blue ethylenediamine both contain a carboxamide-linked diamine spacer off the 8-methoxy group of the pyrene trisulfonic acid backbone. The cadaverine version contains a 5-carbon spacer, while the ethylenediamine compound has only a 2-carbon arm. Both can be coupled to carboxylic acid-containing molecules using a carbodiimide reaction (Chapter 3, Section 1). Since Cascade Blue derivatives are water-soluble, the carbodiimide EDC can be used to couple these fluorophores to proteins and other carboxylate-containing molecules in aqueous solutions at a pH range of 4.5-7.5. The reaction forms amide bond linkages (Figure 9.39). 

Figure 15.14 The NHS ester of a pyrene butyric acid derivative can be used to modify a carbon nanotube by adsorption of its rings onto the surface of the tube. The NHS ester groups then can be used to couple amine-containing molecules to form amide bonds.

The molecules in the second row of this figure show localized orbitals of all types. The first on the lower left, pyrene, has type tt 2 on the outer branches containing two non-joint atoms, type jt 3 on the outer branches containing three non-joint atoms, and a type rr 4 on one of the inner joint atoms. Benzpyrene, in the center of the bottom row, is similar to pyrene in its upper part and to naphthalene in its lower part. Correspondingly, the localized structure is in fact similar to that of pyrene in the upper part and similar to that of naphthalene in the lower part. In the center of the molecule, where these two partial systems are fused, a sort of compromise is reached by a suitable deformation of what was a pure ir 4 orbital in pyrene. The molecule at the lower, right, anthanthrene, has a rather ingenious combination of interlocking localized orbitals of type 7r 2, 7t 3, tt 4 to cover the condensed network. 

It is instructive to look at the refractive indices for a variety of chemical structures (Table 3.1.) What one quickly sees is that polar compounds are not the same as polarizable compounds. Indeed, polarizability is more related to chemical structure features like overall size (higher homologs within a compound family have greater polarizabilities), and presence of conjugated electron systems (benzene is more polarizable than hexane polarizability increases in the order benzene < naphthalene < pyrene). Finally, molecules with large atoms containing nonbonded electrons far from the nucleus (e.g., bromine, iodine) are generally more polarizable. After this brief diversion, now we continue to use refractive indices to estimate polarizabilities. 

Fig. 14 Examples of enantioselective sensors based on excimer formation, (a) Dimeric pyrene-containing y-cyclodextrins and their mechanism of enantioselective sensing upon interaction with a guest molecule (b) cleft-like sensors based on excimer modulation (c) naphthol containing...

Recent literature contains many examples of the construction of cascades [56], Usually they are made by the covalent linking of monomer dyes, which allows strict control of their stoichiometry. The pyrene-Bodipy molecular dyads and triads are examples [57]. Efficient energy flow was reported in a purpose-built cascade molecule bearing three distinct chromophores attached to the terminal acceptor [58]. A combinatorial approach with the selection of the best hits can be applied using the assembly of fluorescent oligonucleotide analogs [59]. 

Lee and Meisel incorporated Py, at levels of 10 M or more, into 1200 EW acid form samples that were swollen with water and with ferf-butyl alcohol. It was concluded based on the /3//1 value for water swollen samples that the Py molecules were located in the water clusters and were most likely near fluorocarbon—water interfaces. It was also concluded, based on both absorption and emission spectra, that the probes had strong interactions with the SO3 groups that were exchanged with Ag+ and Pb + cations in the case of water containing samples. Likewise, the pyrene molecules were rationalized as being surrounded by terf-butanol molecules in that case. However, excimer formation (due to the presence of adjacent pyrene molecules) in the ferf-butyl alcohol system suggested the loss of cluster morphology-... 

The 0.1% polymer derivative contains about one molecule of pyrene per macromolecule, whereas the 5% one has 50 to 60. The distribution of ligand on the polymer is at best binominal.42 Thus a significant fraction of the former derivative contains two to five molecules of pyrene per macromolecule. It is surprising to find excimer formation in the 0.1% derivative since so few molecules are on a single polymer chain. It seems apparent, therefore, that in aqueous solution these moieties on the polymer are clustered in the ground state so that excimer formation is facilitated. 

Electron tunneling between organic species was first detected, by direct kinetic experiments, for reactions of the biphenyl anion radical with naphthalene and pyrene [11] and triphenylethylene [12], As is known, upon irradiating vitreous solutions containing biphenyl or pyrene, Py, these acceptors react with electrons to form Ph2 and Py with characteristic optical spectra [13]. Ph2 particles have been found [11] to enter into the electron exchange reactions at 77 K with naphthalene, Nh, and pyrene molecules in mixtures of ethyl alcohol and diethyl ether (2 1). 

During the y-radiolysis of vitreous solutions containing only biphenyl (0.1 M) or only pyrene (0.02 M), the yield of Ph2 and Py- at 77K is high enough for them to be recorded at an irradiation dose of 1019 eV cm-3. At 77 K these particles have been observed to decay spontaneously (Fig. 5), evidently, due to proton transfer from alcohol molecules (the most probable process in the case of Ph2 anion radicals [14]) or to recombination with counterions formed during radiolysis. Naphthalene and pyrene additives to solutions of Ph2 essentially accelerate the decay of the Ph2 anion radical at 77 K which is naturally accounted for by electron transfer from Ph2 to Nh and Py. In agreement with this conclusion the decay of Py in the presence of Ph2 is slower than its spontaneous decay in the absence of Ph2. ... 

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